Srobinsonx2 Carb Tuning

[srobinsonx2]

Ok, I have read books, forum threads, and articles, watched videos, and asked experts about tuning a carburetor. I have a basic understand but have never done this before. After doing research, I still have some questions. I hope to do two things with this thread. One, document my process with all the details. Two, I will asked questions and hopefully capture the answers here for all to share. I am sure most of the answers can be found in threads through out the FFR forums. But, I have not find them in one place that is simple to follow and in enough detail for this amateur. So, here we go.

It might help if I share some information about my set up.

- Engine is a Levy Racing Stage 4 347. I don't have specific part numbers or data. Per the website "steel crank, I beam rods, Forged pistons, Custom hydraulic roller cam, Victor Jr. cylinder heads, Victor 5.0 or Victor Jr. intake. It is 10:1 compression and runs on 91 octane pump fuel. Horsepower is 420 bench dyno with a properly tuned EFI or 450 with a Holley 650 pro series carburetor. 6000 rpm shift point with a 6500 rpm rev limit "

Transmission is a T5 from Levy Racing as well. I think is it a "super alloy" to handle the higher power of the 347.

Rear end is a Ford 3.55 rear end.

Carb is a Quick Fuel 750 SS. It has mechanical secondaries with an electric choke. I have a 1/2" phenolic spacer under the carb to help with heat.

Ignition system is MSD 6AL with MSD Blater 3 coil. I am using Taylor Thunderbolt spark plug wires.

Timing is set to 14 degrees BTDC at idle and gets to full advance of 35 degrees between 3000 and 3500. I will verify this during the tuning.

I will start on the tuning tomorrow. Hopefully this helps others.

[Gordon Levy]

The engine makes a bit more power than that now over when I wrote that. Pleases to start is power valve, float level and proper setting of the 4 corner idle circuits. Next would be possible jet and/or pump cam settings.

[srobinsonx2]

Thanks Gordon. More power......ME LIKEY!!! I am going to try and tackle all of those. I have a LM-2 wideband O2 meter coming. Hopefully I can get this baby all dialed in and have something that will make your proud.

If you see me headed off the cliff, feel free to point out the error of my ways.

Just out of curiosity, what do you think my engine will make at the wheels if tuned properly?

[Gordon Levy]

Depends on the dyno but 375+ isn't not out of the question.

[bobl]

A couple of things to check before you get too involved in the carb. First make sure your timing is staying steady throughout the idle rpm range. If it moves due to slop, weak springs, etc. you'll never get it to hold a steady idle. Vacuum advance can wreak havoc on idle also, but it appears you do not have one. Secondly, open the choke setting all the way so it does not interfere with your idle settings. Once the idle is set you can readjust the choke. Only adjust idle after it's fully warmed up.

If you cannot get a satisfactory idle, there are ignition boxes that have programmable timing curves and idle control which would certainly solve your problems.

Bob

[bobl]

Question for Gordon. You've built and dyno'd many of this engine combination. Is the carb you send with that engine rejetted based on your testing, or is it right out of the box? Would you expect it to need rejetting in an installation like this? Shannon is at low elevation and I believe your shop is located at quite a bit higher elevation.

Bob

[srobinsonx2]

A couple of things to check before you get too involved in the carb. First make sure your timing is staying steady throughout the idle rpm range. If it moves due to slop, weak springs, etc. you'll never get it to hold a steady idle. Vacuum advance can wreak havoc on idle also, but it appears you do not have one. Secondly, open the choke setting all the way so it does not interfere with your idle settings. Once the idle is set you can readjust the choke. Only adjust idle after it's fully warmed up.

If you cannot get a satisfactory idle, there are ignition boxes that have programmable timing curves and idle control which would certainly solve your problems.

Bob

Thanks Bob. Here is what I have for timing. 14 degrees BTDC at idle. I have checked this a couple of times over the past months and it is always 14. The timing goes to 35 degrees BTDC when the rpms get above 3000 rpm. These don't seem to change.

I did open the choke today to make sure I wasn't setting the idle while on the high idle cam. I then set it back where I had it. Tried a cold start after my idle tune today with much better results.

Thanks for keeping an eye on me. If I can get my engine to run half as well as yours I will be happy. Any advice or oversight is appreciated. We need to get together and go for a drive.

[srobinsonx2]

Started on my idle tune today. First things first. I remove the carb and made sure my T slots were set properly. According to the experts the slot should be 0.04-0.06 inches. Seems pretty tough to measure so I used the rule of thumb that the T slot should be a square. I started with the primaries (front). Here is where I ended up with the fronts.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74061&d=1506212156

If you notice the T slot on the right is open more than the T slot on the left. Is that normal? I kind of split the difference and had the left less than a square and the right just a little more than a square. Let me know if something looks off. I adjusted this T slot exposure by turning the primary idle speed adjustment screw. For those that don't know where this is (like I did), here is where it is (circled in red)

http://thefactoryfiveforum.com/attachment.php?attachmentid=74063&d=1506213334

Next I decided to expose a little bit of the secondaries (rear of the carb) T slots. I had these completely closed before and could not get a decent idle without opening up the primary idle speed adjustment. Here is where I set the secondary T slots. Again the one on the left is not as open as the one of the right. Same as the primary. Again this looks weird so let me know if I might have a problem. As you can see these are not quite a square.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74060&d=1506212147

I adjusted this with the secondary idle speed adjustment screw. It is located on the bottom of my carb. Again it is circled in red.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74064&d=1506213349

The red arrow on the right is pointing to the manifold vacuum port on the front of the carb. This is where I attached my vacuum gauge.

After getting these all set, I turned the four corner idle mixture adjustment screws out to 1 1/2 turns and remounted the carb. I started the engine (started easily) and let it warm up to 180 F. I then let it run for another 5 minutes to make sure everything was up to temp. I then connected my timing light (which I am using to monitor rpms) and the vacuum gauge. I then started adjusting the idle mixture adjustment screws (IMAS). Here is what I did.
- Started at the passenger rear IMAS and turned it in 1/4 a turn and looked at the rpm and vacuum. It went up so I turned it back to 1/8 a turn.
- Turned the remaining 3 IMAS screws in 1/8 a turn.
- Continued this process until I got the following readings on my rpm and vacuum gauge.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74059&d=1506212137

- At this point I had all IMAS open 7/8 of a turn. When I made one more adjustment on the IMAS, the rpm and vacuum went down. So went back to the previous setting and stopped.

In the picture the vacuum appears to be around 7 " of Hg vacuum. That isn't exactly correct. The average was actually 8" of Hg and was bouncing between 7 and 9.

The rpms were average around 950 and bounced between 930-980. It idles very well.

I took the car for a short drive and it ran very well. Seems to be responsive with no bog or stumble.

I also got my LM-2 in today.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74058&d=1506212127

I marked the bung location on the passenger side exhaust. I will remove that side pipe and get the bung welded in this week.

Let me know if you see any mistakes or issues. Those uneven T slots are a little concerning but might just be my lack of knowledge. Thanks in advance for the help.

[Gordon Levy]

Out of the box, I can tune and set up a carb for here but I have found the air in different places way to different for me to take a good stab at it. Example, I built a car for someone in the northeast. I dyno tuned the car and set the carb very rich for my air feeling it would be close for where it was going. It wasn't, it was super lean so I always recommend proper tuning for you area.

[boat737]

Time to show my ignorance. What is a T Slot? Can you point it out in your pictures? Is it an Idle only setting? Thanks.

[srobinsonx2]

Time to show my ignorance. What is a T Slot? Can you point it out in your pictures? Is it an Idle only setting? Thanks.

The "T slot" is slang for the Transition slot. It provides gas between the idle circuit and the other "main" circuits. The T slot actually looks like a slot and what I exposed is just the very bottom of the slot. You can see it in this pic. I have a blue arrow pointing to it.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74065&d=1506218469

As you can see the one with the arrow pointing to it has more exposed than the one on the left. I don't know if this is correct so we will see what the experts say.

Hope that helps. You just exhausted my knowledge on the old "T slot". :)

[Gordon Levy]

I have always used the 4 corner idle screws a bit different. I have found having all 4 set that same ends up being rich. I usually start the front at 1.5 turns and the rear at 1/2 turn. Using the fronts to get the idles where I want it and use the rears to smooth the idle out. I average 1.25-1.5 turns on the front and 1.4-1/2 on the rears.

[Gordon Levy]

What kind if vacuum are you making? I beleive that car comes with a 4.5 power valve and may require a 2.5.

[srobinsonx2]

What kind if vacuum are you making? I beleive that car comes with a 4.5 power valve and may require a 2.5.

I am getting 8" of Hg at idle. Does a 4.0 power valve sound about right?

Thanks Gordon.

[boat737]

The "T slot" is slang for the Transition slot. It provides gas between the idle circuit and the other "main" circuits. The T slot actually looks like a slot and what I exposed is just the very bottom of the slot. You can see it in this pic. I have a blue arrow pointing to it.

As you can see the one with the arrow pointing to it has more exposed than the one on the left. I don't know if this is correct so we will see what the experts say.

Hope that helps. You just exhausted my knowledge on the old "T slot". :)

Thanks "S". I'm not getting into any engine tuning as of yet, still getting past the go-kart stage. I'm putting the body back on for the 2nd time soon, to put some miles on the car, at which point I'll need to address my 2 mpg issue. (I have 16 miles on the car, and it's gone through 7 gallons of gas.). I'll be following your thread with great interest. (although, my carb is a Holley 750, so... We'll see.)

[ThickCobra]

Srobinsonx2,

I am at the same place you are and plan to work on the carb tuning this week. Interesting about Gordon's comment about tuning effected by different locals. My engine was built by Mike on the East coast and I'm in the Midwest. I checked my mixture screws setting the other day on my quick fuel HR 780 cm with vacuum primaries and secondaries. They were all at approximately 1/2 turn out. Should be interesting.

But, I do have another observation. I see you have a 1/4" ID nose running from the right valve cover to the back of the carb (same as mine). It was mentioned to me that this could be a source of a vacuum leak and that i may want to consider capping the tube at the rear of the carburetor and venting the valve cover pvc to a catch can. Maybe the experts could weigh in on this??

[srobinsonx2]

Srobinsonx2,

I am at the same place you are and plan to work on the carb tuning this week. Interesting about Gordon's comment about tuning effected by different locals. My engine was built by Mike on the East coast and I'm in the Midwest. I checked my mixture screws setting the other day on my quick fuel HR 780 cm with vacuum primaries and secondaries. They were all at approximately 1/2 turn out. Should be interesting.

But, I do have another observation. I see you have a 1/4" ID nose running from the right valve cover to the back of the carb (same as mine). It was mentioned to me that this could be a source of a vacuum leak and that i may want to consider capping the tube at the rear of the carburetor and venting the valve cover pvc to a catch can. Maybe the experts could weigh in on this??

Thanks ThickCobra. I did remove and cap the large manifold vacuum line you describe during the idle tuning and it didn't change at all. I will keep your comment in mind. That might be a good trick if I see the idle performance change drastically.

[srobinsonx2]

A couple of questions for the group. Since I know my manifold vacuum at idle, I was going to get a new power valve coming my way. It appears that most carbs only have one power valve (on the primary side) but some can have two. Does anyone know what a stock Quick Fuel SS 750 has? As stated above, it is mechanical secondary and should be set up just like it was out of the box. So two questions:

1. How many power valves do a need? 1 or 2
2. Manifold vacuum is 8" of Hg and I was going to get a 4.0 power valve (the Quick Fuel "four door" type). Should I get a 3.5 and 4.0?

Thanks.

[ThickCobra]

Can you share where you sourced your LM 2 kit. And, it comes with a bung?

[bobl]

That vacuum reading seems a lot lower than I would expect. Do you have the cam specs? You might double check for a vacuum leak. My engine makes 12" at 800 rpm idle and that's with the stack injection. My cam is 233/242 duration on 112 lsa. Gordon should know if that is what he's seen on that particular build before. Might be just the gauge.



I am getting 8" of Hg at idle. Does a 4.0 power valve sound about right?

Thanks Gordon.

[johnnybgoode]

One of the things you can do to make setting the idle easier is the take that secondary throttle stop set screw out from the bottom of the carb and turn it around and put it in from the top. You can then set the secondary stop from the top of the carb without having to take it off. Just hold the throttle wide open (with the motor off of course) and adjust the set screw from the top. I normally set the primary T-slot and then fine tune the idle with the that secondary set screw. Scott

[srobinsonx2]

That vacuum reading seems a lot lower than I would expect. Do you have the cam specs? You might double check for a vacuum leak. My engine makes 12" at 800 rpm idle and that's with the stack injection. My cam is 233/242 duration on 112 lsa. Gordon should know if that is what he's seen on that particular build before. Might be just the gauge.

Thanks Bob. Maybe Gordon will chime I with some specifics or let us know if 8 sounds right. Just in case, I will get another gauge to verify.

[Gordon Levy]

8-10 is about right

[srobinsonx2]

Can you share where you sourced your LM 2 kit. And, it comes with a bung?

ThickCobra,

I bought the LM-2 Kit from Amazon. Here is a link. https://www.amazon.com/gp/product/B001QFL8KE/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

It comes with all the components. This is the "complete" kit. Just a note, the kit I got did not come with the software. It appears it is now a download via their website. Hope this helps. Here is picture of the kit with all the parts.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74124&d=1506292827

You can see it comes with the brain, an SD card, manual, power cord, O2 sensor, O2 sensor cable, bung, plug, OBDII cable, analog cable, and USB cable.

[ThickCobra]

ThickCobra,

I bought the LM-2 Kit from Amazon. Here is a link. https://www.amazon.com/gp/product/B001QFL8KE/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1

It comes with all the components. This is the "complete" kit. Just a note, the kit I got did not come with the software. It appears it is now a download via their website. Hope this helps. Here is picture of the kit with all the parts.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74124&d=1506292827

You can see it comes with the brain, an SD card, manual, power cord, O2 sensor, O2 sensor cable, bung, plug, OBDII cable, analog cable, and USB cable.

Srobinsonx2,

Thanks much. I know you're working thru your issue, so I certainly appreciate you sharing.

Jay

[srobinsonx2]

So I went ahead and ordered some tuning parts. Not sure exactly what I need so let me know if I am way off base.

According to the specs for my 750 SS I have a 4.5 power valve, 74 primary main jets, and 84 secondary main jets. The idle air bleeds are 70 and the high speed air bleeds are 31. The air bleeds I verified.

Here is what I have coming my way:
- 4.0 and 5.0 power valve
- 75-110 main jet assortment (2 of each)
- 35-45 air bleed assortment (4 of each)
- 75-85 air bleed assortment (4 of each)
- fuel bowl vent baffles (I have a hard braking engine stall)
- new vacuum gauge to check my current gauge.

Carb tuning isn't really cheap but I can return some of this if I don't need it.

[Gordon Levy]

Bet you will end up with a 72 in the primary

[CraigS]

They really screw you on the air bleed assortment. The chance of needing 4 bleeds the same # I thought was about 1% so I ordered my bleeds individually. Kind of a pain though coming up w/ a nice box to keep them in. It's been a couple years since I had my carb off but I don't remember the T-slots being different left to right. Anyone have thoughts on that?

[NAZ]

Remember that when comparing vacuum readings with folks across the country there will be some differences due to altitude. Your vacuum gauge will read ~1" lower for every 1,000' of altitude ASL. So unless you're given a comparison vacuum reading at altitude it's going to be hard to make any valuable comparison. I live at 7,000' ASL and the vacuum reading on my car would seem very low to someone based in Florida.

srobinsonx2, don't forget to purchase an assortment of accelerator pump cams and squirters (accelerator pump discharge nozzles) in addition to the other tuning parts.

[srobinsonx2]

Remember that when comparing vacuum readings with folks across the country there will be some differences due to altitude. Your vacuum gauge will read ~1" lower for every 1,000' of altitude ASL. So unless you're given a comparison vacuum reading at altitude it's going to be hard to make any valuable comparison. I live at 7,000' ASL and the vacuum reading on my car would seem very low to someone based in Florida.

srobinsonx2, don't forget to purchase an assortment of accelerator pump cams and squirters (accelerator pump discharge nozzles) in addition to the other tuning parts.

Thanks Naz. I forgot about the accelerator circuit. According to the carb 101 thread and my How to Supertune a Holley book, the accelerator circuit is the last thing to tackle. I will see if they don't have an assortment kit. Thanks again for the reminder.

[srobinsonx2]

I got my bung installed today. I know.....that just sounds wrong. I had to do some searching but I found a shop that would tig weld on my stainless steel side pipes. Tig welding provides a very clean weld.

Here is the bung installed.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74150&d=1506386330

I positioned the bung so that the sensor would just clear the body. Here is the exhaust and sensor installed.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74151&d=1506386341

I will work on tuning later this week. It is suppose to rain the next few days so no real chance for driving it appears.

[Avalanche325]

I certainly don't remember my T-slots being different. I think that is an issue that you need to deal with first. You could have a bent butterfly plate or shaft, or it could be as bad as a warped baseplate. If the mechanical settings are not right, nothing will be. One slot opened too much could make the idle screw on that side ineffective. You will be chasing your tail.

It could be as easy as loosening the butterflies and reseating them. Or giving them a tweak. I swear they look crooked in your first photo. I would give QF a call on that one.

My general advice:
The real and true step one. If you don't have your carb settings card, write everything down. Keep a log of your changes.
Timing first, carb mechanicals 2nd (you have something to look at here), then idle, etc.
As you can already see, there are several different ways to tune a carb. Pick one methodology and stick with it.
Don't jump off the tips and tricks cliff until you try all the down the middle tried and true things and have a specific issue. (I have seen forums with guys trying to fix their idle by changing main jets and drilling their butterflies.)
If you changed all sorts of things and it is not getting better, put it back to factory and start again.

Carb tuning is all part of the fun.

[srobinsonx2]

I certainly don't remember my T-slots being different. I think that is an issue that you need to deal with first. You could have a bent butterfly plate or shaft, or it could be as bad as a warped baseplate. If the mechanical settings are not right, nothing will be. One slot opened too much could make the idle screw on that side ineffective. You will be chasing your tail.

It could be as easy as loosening the butterflies and reseating them. Or giving them a tweak. I swear they look crooked in your first photo. I would give QF a call on that one.

My general advice:
The real and true step one. If you don't have your carb settings card, write everything down. Keep a log of your changes.
Timing first, carb mechanicals 2nd (you have something to look at here), then idle, etc.
As you can already see, there are several different ways to tune a carb. Pick one methodology and stick with it.
Don't jump off the tips and tricks cliff until you try all the down the middle tried and true things and have a specific issue. (I have seen forums with guys trying to fix their idle by changing main jets and drilling their butterflies.)
If you changed all sorts of things and it is not getting better, put it back to factory and start again.

Carb tuning is all part of the fun.

Avalanche325,

Thanks on confirming my fears about the T slot concern. I will call Quick Fuel tomorrow (well, Holley now). My fear is that the baseplate is warped. If you look at both the secondaries and primaries, they both have the same issue but on opposing sides. The drivers primary and the passenger secondary are both slightly more exposed. And their difference compared to their partner is about the same amount. More to follow.

And yes.....it is part of the fun.

[srobinsonx2]

I talked to tech line at Quick Fuel today. They were very helpful and cleared up a few things.

1. The primary side T Slots should be even. Mine are not and more on this below.
2. The secondary T slots are suppose to be slightly different. The passenger side T slot on my secondaries appears to be 0.02-0.04 inches lower than the driver side when compared to the butterflies. Quick Fuel confirmed that is about right and is by design.

Since the primaries T slots should be identical in relationship to the butterflies, I was concerned. I have a dual plane intake and was concerned about different air to fuel ratios across the cylinders. I shared the amount of difference I am seeing and the tech guy said I should be fine and did not recommend any special adjustments or purchasing a new carb. He did say that I could use an open phenolic spacer insted of the ported or 4 hole version I currently have. He said this would help communicate the vacuum, or "signal" as he called it, from both banks to both primary barrels. This made sense.

So long story short is, the Quick Fuel guy says I am ok and should not worry. I tend to trust him since he would profit by erring on the cautious side and saying I need a new carb.

I thought other might be interested in my finding. I will plug along and hopefully do some tuning this week, if it will stop raining. Since I am stuck inside this evening, I will try and load the LM-2 software and do some calibration. I will update you guys on how that goes.

[bobl]

Give me a shout if you run into any questions with that LM2. I've spent a lot of "quality" time with them.

Bob

[srobinsonx2]

Give me a shout if you run into any questions with that LM2. I've spent a lot of "quality" time with them.

Bob

Thanks Bob. I will give you a call later today. It appears I have some software issues. The handheld works fine but am not having much success with importing logs to logworks or connecting the handheld to check the firmware.

[Avalanche325]

I have to say that I REALLY don't like the answers that you got.

Throw an open spacer on to fix the primaries......really? There is a problem that needs to be fixed, not put a Band-Aid on it. I would actually be fixing it myself. First I would check the base plate for warpage. If it is good, I would do some tweaking.

This is my fist QF carb, so maybe I am wrong. For the secondary's, It has been a while, but I don't remember mine being different. All of the tuning books, threads, and videos that I have seen give one measurement. I have never seen one that said, "this much on the driver side and that much on the passenger side." Until one of our resident gurus says different, I am doubting this.

Yes it will run with those suggestions, but it will likely never be right.

[srobinsonx2]

I have to say that I REALLY don't like the answers that you got.

Throw an open spacer on to fix the primaries......really? There is a problem that needs to be fixed, not put a Band-Aid on it. I would actually be fixing it myself. First I would check the base plate for warpage. If it is good, I would do some tweaking.

This is my fist QF carb, so maybe I am wrong. For the secondary's, It has been a while, but I don't remember mine being different. All of the tuning books, threads, and videos that I have seen give one measurement. I have never seen one that said, "this much on the driver side and that much on the passenger side." Until one of our resident gurus says different, I am doubting this.

Yes it will run with those suggestions, but it will likely never be right.

Avalanche325,

Thanks. I appreciate the honest feedback. I wasn't real excited at first but the guy was pretty adamant that it would be ok. I fretted over his response all last night and came to this conclusion. I don't think it will hurt too much to give my current carb a try. If I can't get it lined out, I can always pick up a new carb. Do you see any real danger in this approach? You input is appreciated.

I will take the carb off and check the baseplate for warping. When you say "tweaking" what do you have in mind?

[srobinsonx2]

Made some progress on the LM-2. Got the software installed without issue. I have only issue yet to resolve. I can't get the LM-2 handheld to connect to my computer. I keep getting a USB device error. It is either a bad driver or bad hardware (something with the LM-2 as I checked the cable and USB port on my computer). This ins't a show stopper since I won't be using the LM Programming software. Here are some other learnings so far:

The system is easy to turn on/calibrate and I got the wideband O2 sensor up and running right away (via power in my daily driver). When doing this calibrations I just held the O2 sensor in my hand, let it warm up and then calibrated. When done the O2 sensor reads 20.9. This is not an air fuel ratio but is the oxygen concentration in air. Any AFR above 100, the handheld displays and records the concentration of oxygen and not a true AFR. This can be recorded as such and played back on the handheld. When the log is imported into Logworks 3, the software can only display AFR's between 7.35 and 22.38. Anything above or below this range, the software trends will only display the max or min and not the same value as the display (in my case something near 20.9).

An SD card reader works great to import the logs and pretty cheap.

I got the analog cable hooked up to the tach to measure RPM. Since I am using an MSD ignition box, this system requires I connect to that wire. On my MSD-6AL the tach signal is a gray wire. Found it and made a tie if for it and a ground. Also ran the wire for the O2 sensor and got it installed in the exhaust. I tried to power this all up but ran into an issue. On my car, I installed a USB power supply for charging my phone. The LM-2 has a cigarette lighter plug for power. I bought a USB to cigarette lighter adapter off amazon for a few bucks. It would power up the unit but apparently won't provide enough power to warm up and run the O2 sensor. To verify, I checked this USB to cigarette lighter system in my daily driver and had the same issue. The LM-2 and sensor works great in the daily driver when connected directly to the cigarette lighter. So I am going to pick up a cigarette lighter power outlet tomorrow and replace my USB power outlet. Should be easy and that will allow me to get my tuning system up and running.

I am very hopeful that the LM-2 system will provide good data and allow me to properly tune my carb. But be aware that it appears the LM-2 does have a learning curve and a few idiosyncrasies that one must navigate to use the system proficiently.

[Gordon Levy]

FYI, I have found 1/2" open spacer on that really helps the upper mid range and top end

[bobl]

Made some progress on the LM-2. Got the software installed without issue. I have only issue yet to resolve. I can't get the LM-2 handheld to connect to my computer. I keep getting a USB device error. It is either a bad driver or bad hardware (something with the LM-2 as I checked the cable and USB port on my computer). This ins't a show stopper since I won't be using the LM Programming software. Here are some other learnings so far:

The system is easy to turn on/calibrate and I got the wideband O2 sensor up and running right away (via power in my daily driver). When doing this calibrations I just held the O2 sensor in my hand, let it warm up and then calibrated. When done the O2 sensor reads 20.9. This is not an air fuel ratio but is the oxygen concentration in air. Any AFR above 100, the handheld displays and records the concentration of oxygen and not a true AFR. This can be recorded as such and played back on the handheld. When the log is imported into Logworks 3, the software can only display AFR's between 7.35 and 22.38. Anything above or below this range, the software trends will only display the max or min and not the same value as the display (in my case something near 20.9).

An SD card reader works great to import the logs and pretty cheap.

I got the analog cable hooked up to the tach to measure RPM. Since I am using an MSD ignition box, this system requires I connect to that wire. On my MSD-6AL the tach signal is a gray wire. Found it and made a tie if for it and a ground. Also ran the wire for the O2 sensor and got it installed in the exhaust. I tried to power this all up but ran into an issue. On my car, I installed a USB power supply for charging my phone. The LM-2 has a cigarette lighter plug for power. I bought a USB to cigarette lighter adapter off amazon for a few bucks. It would power up the unit but apparently won't provide enough power to warm up and run the O2 sensor. To verify, I checked this USB to cigarette lighter system in my daily driver and had the same issue. The LM-2 and sensor works great in the daily driver when connected directly to the cigarette lighter. So I am going to pick up a cigarette lighter power outlet tomorrow and replace my USB power outlet. Should be easy and that will allow me to get my tuning system up and running.

I am very hopeful that the LM-2 system will provide good data and allow me to properly tune my carb. But be aware that it appears the LM-2 does have a learning curve and a few idiosyncrasies that one must navigate to use the system proficiently.

Yes they need a good power supply. I use a cigarette lighter adapter with clip leads to connect directly to the battery.

Once you get to testing don't be surprised if you end up around 13:1 A/F for best idle. I've never had much luck getting them to idle really lean and still start well and have good throttle response.

[CraigS]

....
Once you get to testing don't be surprised if you end up around 13:1 A/F for best idle. I've never had much luck getting them to idle really lean and still start well and have good throttle response.
I don't pay attention to the idle afr except as a curiosity. I set idle mixture via 'lean best idle' method on a warm engine and that's it. My QF650 was real lean at cruise of 13-1400 and a QF tech recommended, as an easily done and removed test, to open the idle mix screws 1 turn from best idle and drive it and try 1 more turn if needed. Doing that told me the idle system was lean so then I started replacing jets. I was surprised how far up the rpm range the idle system is affecting the engine. At the low throttle openings our cars use at cruise the idle system is effective up to about 1800.

[Avalanche325]

OK. I am probably being anal about the whole thing. You likely could smack on a spacer and tune away. But that kind of stuff bugs me.

Is the carb new or used? If used, I wonder if it didn't have a throttle stop and was romped on. That can bend the primary shaft, or wear the holes in the base plate.

I was poking at the Quickfuel (Holley - *sigh*) site to see if I could get a good shot of the secondary T-slots. I saw the primaries in a couple pictures and they were identical. I didn't see a secondary shot

Keep in mind, I have not had your situation, so I am saying what pops into my head and what I would do. Again, if someone like Gordon or Craig calls me an idiot, laugh at me and move on.

For tweaking, here is what I am thinking.

Check the base plate first, of course.

Always, least aggressive first. No need to come out of the gate like a silverback gorilla. You are just looking for a few thousandths.
I would take the butterflies off of the shaft, and see if any of those are noticeably bent. Check the shaft and butterflies for any flashing or burrs that could be making one sit funny .
Swap the butterflies around, flip them over, etc. See if it gets better.
I would then consider seeing if I could twist the shaft, without bending it. The amount you would need would most likely be imperceptible to make a difference at the edge of the plates. A new one is <$30 if it goes horribly wrong. Heck, you might just want to try a new one. You could leave it in the base plate to hold the ends and center and make use of the butterfly mounting holes to mount in some handles to get a little leverage on (just a bump, then check).
The cheesier way would be to bend the plates themselves. Again, almost imperceptible would get you enough at the edge and not affect the rest of the range. Butterflies aren't exactly a precision device.

[srobinsonx2]

OK. I am probably being anal about the whole thing. You likely could smack on a spacer and tune away. But that kind of stuff bugs me.

Is the carb new or used? If used, I wonder if it didn't have a throttle stop and was romped on. That can bend the primary shaft, or wear the holes in the base plate.

I was poking at the Quickfuel (Holley - *sigh*) site to see if I could get a good shot of the secondary T-slots. I saw the primaries in a couple pictures and they were identical. I didn't see a secondary shot

Keep in mind, I have not had your situation, so I am saying what pops into my head and what I would do. Again, if someone like Gordon or Craig calls me an idiot, laugh at me and move on.

For tweaking, here is what I am thinking.

Check the base plate first, of course.

Always, least aggressive first. No need to come out of the gate like a silverback gorilla. You are just looking for a few thousandths.
I would take the butterflies off of the shaft, and see if any of those are noticeably bent. Check the shaft and butterflies for any flashing or burrs that could be making one sit funny .
Swap the butterflies around, flip them over, etc. See if it gets better.
I would then consider seeing if I could twist the shaft, without bending it. The amount you would need would most likely be imperceptible to make a difference at the edge of the plates. A new one is <$30 if it goes horribly wrong. Heck, you might just want to try a new one. You could leave it in the base plate to hold the ends and center and make use of the butterfly mounting holes to mount in some handles to get a little leverage on (just a bump, then check).
The cheesier way would be to bend the plates themselves. Again, almost imperceptible would get you enough at the edge and not affect the rest of the range. Butterflies aren't exactly a precision device.

Avalanche325.

I hear ya brother. It bothers me too. But it doesn't bother me $600 worth. At least not right now. If I can get it to tune and run well then I can live with it. If I can't get it to tune or there is a risk of engine damage I will spring for a new carb. I know. I have come this far and spent this much but at some point you gotta stop the bleeding. The wife keeps seeing boxes delivered and finally asked, "So how much has this car really cost?" I immediately suggested a nice Italian dinner, a glass of wine, and trip to the mall. These are dangerous times. I need to camouflage, adapt, blend in, and avoid eye contact. Answer no question. Name and rank only. WHAT WAS THAT???.

Sssshhh. I gotta go.

[srobinsonx2]

LM-2 update. I got the 12v power plug (cigarette lighter) installed. Plugged everything in (analog cable, O2 sensor, SD card) including the power cable and powered it up. With the cigarette lighter hooked up directly, the LM-2 powered up as expected and the O2 sensor warmed up (about 15-30 seconds). I cranked the engine and the O2 sensor immediately went from 20.9 (oxygen concentration) to 12-14 as the AFR. I was pleased. The rpm was displaying about 7000. Turns out I didn't have the rpms configured correctly. I followed the instructions and got that lined out.

I then recorded a little bit via the LM-2. I then imported the log into the Logworks3 software. Here is screen shot of the trend.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74274&d=1506645714

I haven't done any tuning so there are probably some things I need to work out. This was just a test of the LM-2. I had some idle, revs and hold at 3000, then some short stabs. I am excited to get to tuning. Now the rain needs to stop.

Here is a short video. Sorry the video is so poor.

https://www.youtube.com/watch?v=gPCqRddH6JQ

[srobinsonx2]

FYI, I have found 1/2" open spacer on that really helps the upper mid range and top end

That's what I got headed my way. I will install it this weekend and report back. Thanks Gordon.

[CraigS]

Once the rain stops take a note pad w/ you to keep track of your recordings. IE #1 = from a stop 1st, 2nd, 3rd about 1/3 throttle, #2 = full throttle 3rd gear, etc. I find this helps cause I have gotten lost some times when I come back to the house and have 5-6 recordings. Especially for the full throttle stuff where I needed to drive 5 miles to get to a spot I could do that w/o pi$$ing someone off. Good luck and have fun!

[bobl]

Shannon, I was under the impression the carb came with the engine from Gordon. I'm now realizing that you must have acquired it elsewhere, which clears a few things up in my mind. Was it new?

[srobinsonx2]

It came with the engine. But I haven't asked Gordon to help in any way. Sure don't want folks to think he dropped the ball. Honestly, I don't feel right asking him to replace it or anything like that. I am an amateur and can not rule out this being something I did.

I did take the carb off and think I found the issue. I will post am update a little later.

[srobinsonx2]

After some consideration I came to the conclusion that Avalanche325 was probably right and the misaligned T-slots should get fixed. So with a little trepidation, I decided to take a stab at "fixing" the problem. Upon careful inspection, it was clear that the driver side butterfly valve was slightly tweaked. I used a pair of needle nose pliers and a screw driver to ever so carefully realign that butterfly. Took me a few minutes but I managed to straighten it out without disassembling the carb. I tried to get some pictures but they turned out blurry and you could not tell much. The carb is back on so, during the next removal, I will try and get a better picture. Once reinstalled, I set the idle circuit again. I used my LM-2 and a vacuum gauge. My second vacuum gauge came in this week so I took the opportunity to verify the one I had was accurate. I confirmed that they both read the same. So onto the tuning. I started from scratch on the idle circuit. Primary T slots set to at square, the secondary T-slots closed, and the idle mix screws out 1 1/2 turns. That gave me a rich idle (11.5-12 AFR), 800 rpm, and a vacuum of 8.5. I turned the idle mix screws in until I got the highest vacuum and the highest idle. That ended up being 950 rpm and a vacuum of 10" of Hg. The AFR ratio at this point was right around 13 (between 13-13.4). So I felt good about my idle set up.

With the new vacuum reading, the power valve needed to be changed. I removed the primary side. It was very easy. I used a 5/16" socket to remove the four bolts on the front corners of the bowl. I tapped on the top of the bowl with my hand and the bowl came right off. I then tapped on the metering block with the end of my socket driver and it came right off as well. Here are the parts disassembled.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74382&d=1506783839

I then took the power valve (PV) out of the metering block. The PV installed was a 6.5. I replaced it with a 5.0 Quick Fuel 5.0 "four door" PV. A 1" wrench fit the PV perfectly. It was not very tight so I reinstalled the 5.0 to the same tightness. Here is the PV and o ring.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74381&d=1506783830

I reassembled the primary side and reinstalled the carb. I also made a vent tube extender that should help with my hard braking. This is only a temporary prototype. If this works well, I will make something that looks nice.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74380&d=1506783821

I used two spark plug wire boots and a short piece of 3/8" fuel line. I cut the vent holes in the top with a razor knife. Not pretty I know but this is just for testing purposes.

Finally, I took the car down the road in my neighborhood to test the idle circuit. I will have to redo this run. I accidently got on the gas towards the end of the run and got out of the transition slot and into the main a little ( I think). I started the run at 1500 rpm and ramped up to 3000 rpm in second gear. I did this by applying just a little throttle with the intent of only exposing the T-slot. Here is the log.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74383&d=1506783940

Magenta is AFR and black is the rpm. It is not bad for the first half but gets a little rich towards the end. Per the experts, the entire run should give an AFR of 13.5-14. I won't change anything at this point. I will wait until I get another run from 1500-3000 rpm but in third gear and staying in the T slot.

[NAZ]

What we do with off-road vehicles is loop fuel hose in a inverted catenary connected from vent tube to vent tube. We then take a long slice out of the center of the hose just shy of half-way through the hose and a couple inches long (linear with the hose so the hose is still one-piece). This all fits under the air cleaner and is about as neat as you can make a home made extended vent. However, I've never had to do this on a street or even a track car that runs on a smooth track (stadium racing is the exception). But if you feel you need to extend the vents, this is a common low-cost way to do it.

But an even neater way is to purchase Holley vent whistles (Holley #59-10). It looks as you carb came without them. The vent whistles fit inside the bowl. There are also anti-spill valves out there but I've never used them so can't comment on them other than I know of them.

[srobinsonx2]

Thanks Naz. I do have the vent whistles. They are the black push in style. I lowered the bowl level in the secondary a little. Hopefully that solves my problem.

Thanks for the home made vent advice. I like that idea.

[NAZ]

Another thing to consider, especially if you run a lower level in the secondaries is fuel starvation during hard acceleration. With these light cars even a moderately powered car can accelerate in excess of 1.6 G's which can slosh fuel in the bowl >50-degrees potentially uncovering the secondary main jets. If you experience this I recommend you get main jet extenders on the secondary side. The kit includes a new float with clearance cutouts for the extenders. This puts the jets farther to the rear so they are not as likely to become uncovered when the fuel sloshes to the rear. Of course that's not a problem on the primary side and not an issue when hard on the brakes as you are off the gas during braking.

Just another tool for your tuner's tool kit.

[srobinsonx2]

That is funny. I have those too. Thanks though and keep 'em coming.

[srobinsonx2]

Here is my idle circuit.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74415&d=1506810586

I ramped from 1500 to 3000 rpm and took about a minute. The blue line is 13 AFR and the red line is 14 AFR. As you can see my AFR was well below 13 the entire run. It does slope a little bit to become more rich as the rpms increase. I also have a funny lean-rich-lean bump at the beginning of the run right at 1500 rpms. I am not sure what this is. So, here is my plan of action:

- Put in smaller idle feed restictors. I will start with 2 sizes smaller. I don't know what size I have so I will have to disassemble and inspect.
- I will hold out on adjusting the idle air bleeds. I think I might need a little smaller IAB to flatten out the slope but I will only change one thing at a time.

What do you guys think about the initial lean-rich-lean condition at 1500 rpm? Any advice. I don't really know what to do there. Maybe I got a little aggressive and the power valve came open to cause the rich condition but I don't know about the lean spikes. Any advice would be much appreciated.

[Gordon Levy]

Change the pump cam position from position 1 to position 2

[srobinsonx2]

I had to order some restrictors/bleeds. They came in today. Summit is great and I usually get items in about 2 -3 days. Here is what I got.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74696&d=1507165398

Based on my previous post, I had determined I needed smaller idle feed restrictors (IFR). The IFRs that came stock on the 750 SS appeared to be 0.031. There were no markings and used some small drill bits to gauge the size. Based on some additional research, others had confirmed the same. So, I had ordered a number of IFR sizes. One larger and two smaller. I decided to put in new IFRs that were two sized smaller so put in 0.029 in on the primary and secondary idle circuits. Here is where the IFR is located on the inside of the metering block. My screwdriver is pointing to the IFR.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74694&d=1507165381

Here is a picture comparing the stock IFR to the new one. The one on the left is the larger stock 0.031 and the right is the smaller 0.029.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74697&d=1507165410

Once I get everything back together, I will go for a drive again and test the idle/cruise circuit like I did before. I will then see if a small change in the idle air bleeds are needed. I won't get a chance to do that until this weekend (work is getting in the way of my hobby).

Finally, I think I see a potential issue that might be contributing to my stall on hard braking. The bowl vent baffle does not completely "plug" the vent opening. I have the black push in style. Here is a picture where you can see around the outside of the baffle.

http://thefactoryfiveforum.com/attachment.php?attachmentid=74695&d=1507165388

I will think about potential solutions to this. Something that might help seal that up? Any thoughts here?

As always thanks for the input and let me know if I am headed in the wrong direction.

[srobinsonx2]

Got the chance to do some more tuning. Based on my previous post, I thought I needed to reduce the IFR down to 0.029. Didn't change much so I reduced them to 0.025. Here is what I ended up with. The AFR started off pretty good but around 2300 rpm the AFR dropped down to around 11.

http://thefactoryfiveforum.com/attachment.php?attachmentid=75021&d=1507511030


I stewed over this a while and came to the conclusion I must have a vacuum leak somewhere that was allowing the PV to open. I had recently put in a chrome PCV on the valve cover. I replaced it with the one that came with my engine and that little dip went away. The smaller IFR didn't do much and it kind of seemed to make the AFR richer which didn't make sense. I decided to start over and put back in the stock 0.031 IFR. I also reduced the IABs on the primary side from 70 to 68. Got the following and felt pretty good. It still has a tendency to go from lean to rich but really close to my target AFR of 13.


http://thefactoryfiveforum.com/attachment.php?attachmentid=75018&d=1507510716


This was done in 3rd gear. I got this funny little spot where the AFR went a little lean at 2600-2700 rpm. I think I let off the gas at this point so I went for another short run in the neighborhood. I got the following data log in 2nd gear. I think it looks pretty good. Interesting that the AFR stays around 14 in 2nd instead of an AFR of 13 I got in 3rd gear.


http://thefactoryfiveforum.com/attachment.php?attachmentid=75017&d=1507510706


With the light cruise circuit dialed in about as good I think I can get, I moved onto the main circuit on the primary side. Here is what I got.


http://thefactoryfiveforum.com/attachment.php?attachmentid=75019&d=1507510727


I could use some advice here. The overall AFR looks good except for the short rich period early in the rpm range. What do you guys think? Should I adjust this?

Once I get the primary side lined out, I will move on to tuning the secondaries with some WOT runs. Any help would be much appreciated.

[bobl]

You're getting pretty deep into this deal. What you are missing is load data. I would hook up a map sensor and log that to know exactly what the vacuum is. Also if the throttle is moving at all during these runs you've got accelerator pump discharge messing with the numbers. If you come to a slight incline the PV may start dumping and conversely you go a little down hill and it closes. You need that map data if you're trying to tune that close.

[CraigS]

You went from 2000 to 4600 in 7 seconds so I guess a 1/3 to 1/2 throttle application. That rich spot at 17 to 18.5 seconds is most likely pump shot. Or possibly it is the PV opening. Either way, I think I would ignore it and move on. You can always come back to this if you find you have a hesitation that might coincide w/ it. As you start w/ full throttle runs, one test I use is to disconnect the linkage so the secondaries don't open. This helps to decide whether you need to adjust primaries or secondaries. I remember someone, Wayne maybe, said that you will end up the primaries on the rich (I think) side if you try to get them perfect by themselves so just use this as an indicator.

[srobinsonx2]

Sorry for leaving this unfinished. I kind of stopped tuning much past the primaries. I don't have a good spot for WOT so tuning the secondary side will habe to wait.

I have been working on my hard braking issue. I tried a number of things without much luck. I will post that later (no computer right now so pics are hard). I ended up lowering my secondary fuel level to the bottom of the sight glass. Seemed to have worked. If it doesn't rain this weekend, I might test it at my first autocross. :)

[CraigS]

I understand. WOT in 2nd happens so fast it's hard to use. WOT in 3rd gets you up to maybe 80mph and makes a lot of noise for a longer time. I had the same problem. Had to drive 10 min to get to a spot where I could do WOT in 3rd. I ended up leaving the LM1 connected for months at a time so I could use it when the opportunity presented itself. Found I could do air bleed jets on the side of the road but any other changes I needed to get home.