Lance's Roadster Build Thread-Carb Tuning Info

[F500guy]

You can also make your own cables to the exact length and size you need. I have a cable crimper if you would like to borrow it.

My initial pricing said that thru that company, they may be cheaper than buying bulk cable and the ends. Once I measure it all, I will get an exact cost, but the web site made it pretty easy to order exactly what you need!

[F500guy]

Latest Growing pain-Noticed on my last trip that my fuel gauge was on "E" . Well, 35 miles on 15 gallons of gas is pretty crappy fuel mileage. Local trouble shooting and I can not get a consistent OHM reading out of the sender. Gauge seems to work appropriately with resistors to indicate level, but the sender is all over the place. Sometimes 0, sometimes very high, well above normal and sometimes high when it should be low and sometimes low when it should be high...

Trudge on!

[egchewy79]

Have you calibrated the fuel sender yet? Do you have the speed hut ones?

[F500guy]

Have you calibrated the fuel sender yet? Do you have the speed hut ones?

Oh ya, more than once and a non-standard. The sender resistance seems to be a moving target.

[Blitzboy54]

Latest Growing pain-Noticed on my last trip that my fuel gauge was on "E" . Well, 35 miles on 15 gallons of gas is pretty crappy fuel mileage. Local trouble shooting and I can not get a consistent OHM reading out of the sender. Gauge seems to work appropriately with resistors to indicate level, but the sender is all over the place. Sometimes 0, sometimes very high, well above normal and sometimes high when it should be low and sometimes low when it should be high...

Trudge on!

Hey there,

My fuel sender did the same thing. Dropped to empty. I have a programmable Autometer gauge very similar to the Speedhut. After much troubleshooting it was the sender. Took me a while because I assumed it was the guage but just like yours the resistance dropped out of the sender. I purchased a new one and now it works fine.

[F500guy]

New Sender-Dorman off amazon 55.00 (auto parts stores wanted over 100.00, got to love and hate on amazon...) and the resistance is 17 ohm empty, 170 or so full-I will put it in today and hope it last.

Seems we the people are now the QC department for this stuff, how can a float with a resistor fail?

[F500guy]

Well,
After a nice vacation to Barcelona, Spain-I am back on the car. Did take a visit to Circuit de Barcelona and watch the opening round of the 2025 season for European Endurance Series, not a bad seat in the house at that track, wish I could go to F1 race there. I got to say, those LMP2 cars are some of the loudest, sitting at the front straight at WOT make the ears bleed...

Back to the Cobra:
1) Got and installed a new Holley 670 Street avenger, will start tuning after I get it running again. Got a carb tuning book by David Vizard- A Real eye opener even though only about 15% of the book is what i need to deal with, most is way over my head for needs and desires. He is a real proponent of vacuum secondaries. I know now why the BP 427 is outfitted with such a big carb, even though most non-race driving it is probably overkill and why it has to run so bloody rich at part throttle or sudden full throttle. More updates when it is driven.

2) Upgrade of new #2 battery cables-only 76 bucks, all pre-made with the ends, big difference from the tiny #4 now I just need to put them on and get 'er rolling again.
BatteryCables Upgrade.jpg

3)Licensing completed "Insert Party Picture here". Nice trip to the DMV despite the activity for everyone getting the "Real ID" wrapped up. I was in and out in what I would consider a reasonable amount of time. The took my money, used the serial number for the VIN, titled as 1965 Factory Five..... This makes it exempt from emissions monitoring. time to hit the road this summer before I get it painted!

[F500guy]

Got in a couple drives yesterday after the upgrades.

1) Minor tweaking only so far on the carb, better throttle response, will still need to review the info for calibrating the primary pumper, but very positive. Hard to stay in the throttle for more than a couple seconds before hitting the legal speed limit! But the initial throttle bog is very much reduced. Also less smoke on cold start.

2) After a couple good heat soaks, the engine fired right up. Made first official trip to the gas station-have been using fuel cans up 'til now.


Next up-putting on miles, play with pedal layout, seat positioning and learning to heal/toe this big motor on down shifts...

[BUDFIVE]

Lance, Warning, the below is very detailed and not for people who hate carbs-Mike Bray is gonna tease me for this post

I think the BP427 has a pretty big cam(248/258 duration at .050)?
If so, to give it enough air for idle, you will open the primary throttle quite a bit with the idle stop screw. You may move the primary throttle plate into the transfer slot. The transfer slot enrichens the mix as you roll the throttle from idle to cruise—this is not the accelerator pump that sprays fuel out the nozzles at the top center of the carb when you smash the throttle. Anyway, if at idle you are into the xfer slot, the mix will be rich and the idle mix screws will be virtually unresponsive. Further, when you roll into the throttle, it will have a dead bog or lag till the engine draws enough air for the main circuit to correct the mix.

The street Avenger 670 is vacuum secondary but still has 4 corner idle including an adjustable secondary idle stop (most under the carb mounting plate)? If so, flip the carb over and see if the primary throttle plate is too far into the transfer slot. If so, close the primary throttle idle stop till the throttle plate just touches the slot. Then open the secondary throttle plate until it touches its slot—this gives the engine the extra air it needs. Then with the carb back on when you start the engine, the idle speed may be too fast or slow but minor adjustment of primary stop screw should get it back on target. Now the idle mix screws will be responsive and you need to iterate on idle mix vs idle speed stop. The primary transfer slot will now be fully available as you ease into the throttle.

While the change from a Holley 870 to 670 will improve streetability in many ways, this specific idle issue gets worse as you must open the 670 primary more for the same amount of air as the 870.

I went through this exact scenario this summer on my big cam 347-the throttle response improved dramatically and was verified in 3 go-cart sessions. I had to pull the carb twice to get the primary and secondary openings right—my secondary opening stop is on the bottom.
I wrote about this in my build thread post #52.

https://thefactoryfiveforum.com/show...unt-Prep/page2

Vizard’s book has a section on the transfer slots. There are also good videos on this-I can share some links if you need them. Feel free to PM if I can help.

[F500guy]

Thanks for the info, next summer I plan on digging in more to this. I bookmarked that info for now, I am looking forward to playing around with this stuff.

[Mike.Bray]

Lance, Warning, the below is very detailed and not for people who hate carbs-Mike Bray is gonna tease me for this post

You know me! Hahaha

That is just way too much work for me, I don't have near enough energy to try that again at my age. I'm thinking after al those painstaking fine adjustments and then the car sits over the winter with the gasoline in the carb evaporating and leaving behind the ethanol residue in all of those teeny time passages....

Fun story for you, I just bought a 68 SS Camaro to fix up. It's a nice clean recently restored car that just needs my touch. It's currently got a mild 350 SBC, about 300HP, with an Edlebrock intake and, are you ready for this, a carburetor! Oh no!! Plans are to build a big block Chevy and of course install port EFI.

[cc2Arider]

Hey Lance,

Nice that you got your State DMV to title it as a 1965

I'm really hoping I can do the same in my state!

Craig C

[F500guy]

Well, time for a 500 mile report. I clicked thru 500 miles pretty quickly, with only running around town and a couple 50 mile cruises around town and the highway. I have yet to light up the tires and refrained from to serious driving of mountain roads until i had completed my nut/bolt check. Next 500 miles will be putting it thru some more aggressive stuff, pushing a little more and practicing my poor heel/toe to improve down shifting. Compared to the Miata, it is quite the beast, like I mentioned before i is hard to stay in the throttle more than a few seconds and remain reasonable legal speed. Seems I get a lot of waves and folks trying to talk thru the windows at stop lights. Here is some key points

1) 427 Carb-I would do it again if I had never done it. I dropped on the 670 carb and I can roll into the throttle to 6K in first gear no problem. Stop and go traffic, no problem. I will probably go back to the 870 or a 750 DP next summer, but the engine has been working great, no issues. Had the car out yesterday, close to 90 deg, some traffic and all was good. Second gear really punches hard on the on-ramp But, the Holley street avenger as I have read on other forums, hard braking and the engine dies, will need to work on that but really only a problem when doing a good brake check at this point.

2) Turn signals-I opted for manual and really who needs them anyway-Only when I want to be courteous.

3) Primary wire electrical-Since I changed to the 2 gauge primary, no issues with hot restarts.

4)Nut/bolt check-Found a minor issue for my watch list, the toe link connection point to the driver side rear hub has a minor wiggle. That would be poor quality ford part or possible out of tolerance bolt. I may source another bolt as first option, passenger side is rock solid. Early in the build I replaced all the chassis side rod ends with higher quality due to a wiggle in the toe link, they are rock solid on the chassis side.

5) Made some alignment adjustments, and ride height adjustments, the front end seemed a little squirmy under acceleration.

6) Not really happy with pedal geometry, I ended up putting on the Breeze throttle pedal, which if I keep I will need to make sure it is solid and probably hard mount it and not leave it adjustable. I like the toe relief better than the straight bar. I ended up getting some piloti driving shoes, but may still end up re-configuring the pedals. That will take some patience and seat time, would like a bit longer throttle pedal to reach lower towards the floor for my heal to grab.

7)EPAS Eval-Spent the first 500 miles with it turned off, did not seem to be to big a deal. I will turn it on for the next 500 miles. I have a speed sensitive setting so I will set that up to reduce assist at very low speed. It is nice when playing around in the garage...

8)Annoying electrical issue-This is possible related to the RF harness and I will have to troubleshoot some more. I installed a low voltage indicator light I got from Ron Francis and connected it to the dash power supply. When I first start up/engine cold my dash voltage meter reads 12.5. When engine warms and on the road for a bit, it settles about 11 to 11.5. I turn on my headlights, the voltage drops to 10.5 to 11 and the low voltage light comes on. I have verified that all the primary voltage points where the RF harness gets supplied are 14+ volt when idle and system is hot. so, seems a big voltage drop in the harness. Every thing still runs fine, but annoying. I will have to drop the dash and and maybe 1) run separate monitoring ckt wire from my cutoff switch, thus eliminating the RF harness. 2) Check all wire connections at the fuse box and ignition switch for and issues. 3) Ditch the low voltage light and install a low oil pressure light. Probably save that for a winter project.

9) Brakes-I changed out the pads from the kit supplied wilwood BP10 to the wilwood BPQ, has a higher coefficient of friction . The BP10 were fine for streeting, but I wanted to have some more aggressive stopping power and the prospect of little dust was appealing, you know because you know! I will try them out for 500 miles and if I am still not satisfied, well I will change again. (I have Hawk HPS+ on my Miata and really like them I also ran the Hawk DTC-30 on my Miata and they were the bomb, but to noisy and dusty for street)

All in, I am a happy camper and hope to hit 2k before I drop it off for final body work and paint so Ken can fix all my sh**** that I messed up on the body work. Final color and paint scheme has been selected. Well, actually 4 different paint schemes depending on the cost and input from the painter so hopefully next driving season it will be sporting final colors.

[F500guy]

####8)Annoying electrical issue-This is possible related to the RF harness and I will have to troubleshoot some more. I installed a low voltage indicator light I got from Ron Francis and connected it to the dash power supply. When I first start up/engine cold my dash voltage meter reads 12.5. When engine warms and on the road for a bit, it settles about 11 to 11.5. I turn on my headlights, the voltage drops to 10.5 to 11 and the low voltage light comes on. I have verified that all the primary voltage points where the RF harness gets supplied are 14+ volt when idle and system is hot. so, seems a big voltage drop in the harness. Every thing still runs fine, but annoying. I will have to drop the dash and and maybe 1) run separate monitoring ckt wire from my cutoff switch, thus eliminating the RF harness. 2) Check all wire connections at the fuse box and ignition switch for and issues. 3) Ditch the low voltage light and install a low oil pressure light. Probably save that for a winter project.####

So I tore my dash out to investigate this issue. Root cause is the "Zero Dimmer" from Speed hut that is used to adjust the LED gauge brightness has a "Gauge Power Supply" Output that is supposed to power the regular 12 volt supply to the dash gauges. Well, it is not a pass thru from the power supply, some how regulated or pulled off the lighting ckt functions and is not 12 volts. Static condition with the gauges hooked up it was about 10.5 volts (car off and battery at 12.3 volts), lighting my low voltage light and show very low on the dash volt meter about 10.5 . So, I disconnected that lead to the gauges and ran a separate supply to the gauges power and all looks good. Before I put everything back together, I have a tech support call out to speed hut to ensure that the "zero dimmer" can run without that output loaded. All gauge lighting is working fine.

@@@@Update-Speed hut confirmed that I do not have to load that output-good to go and they did say usually .5 volt drop, (but i am closer to 1.25)

[F500guy]

So, kind of like tweaking, and not drug related...I added some engine bling. I did calculate the air flow and it is not what a 427 should have so I will not use the air cleaner for tuning, but sure looks nice

Engine Bling.jpg

[cc2Arider]

Looks Good Lance!

Can you reveal the Supplier source for that, or shall it "not be named"?

Craig C

[F500guy]

Ansen made this

[cc2Arider]

Hi Lance,

I looked thru FMan's build several years ago for inspiration, and I believe he used the same filter assembly...

What were the air flow numbers that informed you that the assembly still might not be adequate for your engine?

Craig C

[F500guy]

Finally got a first Data Run with my AIM EVO4s/Smarty Cam system. I am a bit rusty on my squiggly lines stuff so I will for sure re-learn some more this winter. Still have a couple sensors to add and system clean up for the wiring. Seems that the last software update really fubar'd some stuff so I have a couple good head scratcher issues to work thru and hopefully they will get addressed in future updates. AIM is usually pretty receptive to looking at logs and assisting. I have never worked with the AFR, so some learning there for sure and it is running pretty rich across the board.
Cobra Data Run.png

[Grubester]

...or maybe data inputs that can handle monometer inputs, such as from a 0-2 in Dwyer monometer and/or air velocity data input. Be great for resolving air flow issues in and around the radiator and the engine bay. Seems this is often an area of discussion.

[F500guy]

So, this is where the EFI folks look the other way, nothing to see here! I decided to put off paint until next year, so I inevitably thought "what I am going to screw with before the driving season ends?" I decided to pull in my purchase of my "forever" carburetor and get it set up. Fall here in NW Oregon has been great, many more weeks of driving than I thought I would get so I was able get through my tuning. Lengthy post but may help a future carb person! It was a bit of a circus at times, and I spent some time waiting for jets and pump nozzles and such.

What I got-Holley Street HP 750 double pumper, no choke.

Problems I created for myself-( this was the circus part)
Forgot to put a boot on the spark plug, it burned real nice on the exhaust manifold, had trouble with my throttle position sensor, kind of fixed but not sure it is reliable as installed, burned my data download cable 3 times across the manifold and the side pipe Attention to detail, lots of hot stuff. My timing light clamp ended up contacting the header, almost melting closed. Made some initial assumptions, had to back out but at the end it was close to my initial assumptions.

What I had to learn, Timing for the SBF and a little self-study on the vacuum advance, how to adjust the MSD distributor mechanical advance.
Study Material-Found great stuff on the other Factory five site about tuning and timing, Wayne has a great how-to article for setting up a carb https://www.ffcars.com/threads/carb-tuning-101.273476/

I wont hit all the details, the tuning is described really well in the link. For Timing, (vac Advanced disconnected) I ended up with 15 deg BTDC at 800 idle, 35 deg at about 3300. Mechanical advance starts about 300, by 800 it is about 2-3 deg, and my distributer is set for 21 deg max advance. I changed the springs in the distributor to get full advance about 3300.

I run E10 fuel, 10% ethanol here, so that makes a Lamda of 1 =14.1 AFR (pure gas would be 14.7 AFR) so I tried to adjust my set points for the lower AFR, or use the lambda value, my data system gives both numbers and I can set it for what fuel I run.

My Carb does not have adjustable Idle Fuel restrictors or Power valve fuel restrictors, they would have to be blocked or drilled if I wanted to get a more exact number. I cheated with the 4 corner screws, leaned them a tick after getting best idle, I found this would not effect the idle, but would affect light cruise test.

Still a little blurry on accelerator pump, I have no bogs and loud pedal does its job, seems most of what I found was a bit subjective-“works with no bogs, does not dump black smoke”
A bit of work with all test runs, If I did it again, probably only need ½ the test runs.

Runs very, very well. I went 1 jet size passed what I ended up as final setting and started to get a lean bog with some on/off throttle stuff so I am sure this motor probably would rather be a tad rich than a tad lean. If I needed to tune for a competitive advantage, I would need a dyno to see what the motor likes best for AFR or do some 0-60 or ¼ mile runs-Not good to do out in public! Very happy with the results and knowledge gained, Think I may play with my other carbs next year, may be able to get the 670 to be a fuel miser. I attached a couple example pictures of my data and my final set up information. Pictures are from my 2nd to last run, you can see on 40-60 pull AFR was not dipping and stayed up to lean, so this lead me to go back up 1 jet size on primary and secondary mains. I then changed my plugs and took a 80 mile cruise today, works wonderfully, I am over 1400 miles this summer-missed my goal of 2k, but still happy!

75 MPH steady state 1.jpgCarb and timing Settings.jpgSteady state 30 mph 2.jpg45 to 60 pull anomaly 3.jpg

[F500guy]

Last week I hit the 2k mile mark, made it before conclusion of year 1 of official licensing. So work begins to make changes and repairs for the next driving Season.

1) Replaced all the plug wires, this was because I burnt 1 up last year and my new set has the heat wrap and are 3 mm larger than my previous ones, so last year I replaced 1 and now I finally completed the matched set. I should have added some bling wires, it took a bit more effort than I expected. Most of the wires fit well, 1 was a bit short and 1 was a bit long, but they all made it! A simple SBF kit from Moroso, had to add the end to the coil wire after trimming to size.
New Plug wires.jpg

2) Repaired my windshield chip. Used Rain-X kit from Amazon only about 13 bucks. Results-Better than expected but not perfect. The resin penetrated the 1/2 moon crack, but not to the very ends. There is still a small surface blemish. Bit of a learning curve there, but would use it again, kit can be reused and there is a lot of resin left after this 1 small repair.
Post Repair.jpgPre window Chip repair.jpg

3) Added a Throttle position Sensor to the my carb. My first attempt last year was kind of jenky and not working well. This part I got off the Internet for Holley 4b carbs and was able to splice a cable to it for my data system. So far testing it is very robust and will proved the ability to get data about what happens when the secondary operation starts since I will now know when I am >50% throttle. Kind of fun to know how deep into the throttle at different times, like I noticed a 30-60 run entering the freeway on-ramp in 2 seconds.
Throttle Position Sensor.jpgTPS Installed.jpg

4) Report out on Wilwood BPQ pads-Super happy with them. went to clean the wheels the other day and very little residue, most just road dust and they stop great, way better than the BP-10 compound that shipped with the kit.

5) First coolant leak, looks to be the lower hose connection, radiator side. I tried tightening, re-orienting the clamp and still a couple drops a day. I will monitor to make sure that there is not a radiator problem, which would get addressed at paint/bodywork.

6) Continue to tweak the carb, looking for some more fuel efficiency with out tanking performance-I swapped the pump cams to red in the primary and white in the secondary and down sized my primary squirt-er nozzle to try and lengthen the primary shot, reduced primary main and increased secondary main Super happy with the performance as it is Zoom-Zoom it goes!

7) Outlawing the wife from having open cans in the car, 1/2 full and still got spilled...I was not even grabbing much throttle at the time!

8) Next up is finishing my high mount brake light, I have had idea and supplies for a year, wiring is present and just need to get my rear in gear on this one.

[F500guy]

So I made an attempt to soften the door hinge. This is the first run and I will sit on it and see how I like it before I do the rest. I started with some 1/8 inch closed cell foam with sticky on one side, put down 2 layers

Door Hinge Wrap Prep.jpg

Then I wrapped it with a layer of upholstery stuff I had laying around and secured at both ends with Zip Ties. Not show car quality, but I do have some left over leather that I could use and look a bit better

Door hinge wrap.jpg

[Stangrob]

Looks good!

Rob

[egchewy79]

So I made an attempt to soften the door hinge. This is the first run and I will sit on it and see how I like it before I do the rest. I started with some 1/8 inch closed cell foam with sticky on one side, put down 2 layers

Door Hinge Wrap Prep.jpg

Then I wrapped it with a layer of upholstery stuff I had laying around and secured at both ends with Zip Ties. Not show car quality, but I do have some left over leather that I could use and look a bit better

Door hinge wrap.jpg

Consider tennis grip wrap or bike handlebar wraps if you wanted to go this route. It might also give you some options for color/patterns.

[PNWTim]

Following the theme you might also be able to use some really high density foam covered with a stitched steering wheel wrap. You could cut it into four pieces and stitch it in place on the back side, would almost look factory.

[F500guy]

I mostly finished my high mount brake/backup light combo. I originally wanted something functional that could be removed if needed, non permanent and still look decent. Well, I hit functional and can be removed...Final product did not really meet my cool factor. I will leave it on for now and maybe think of something different or just jet the small lights that Breeze has and forget about the back up part. There is still time to look at something else before I get the body worked over.

I started with some Oznium LED's the small 5mm ones, a piece of carbon fiber and a fire extinguisher holder from H3R I drilled and tapped the fire extinguisher holder and made a small plate from some carbon fiber that I had. I then installed and wired 2 white LED's for Back up and 4 red Brake light leds for each side. Works great, thinking of getting one of those "flash your brake lights" controller some real annoying fun. Any way, done but not super excited with the results, concept was way cooler.

Back Side.jpgFront Side Of Plate.jpgMount Picture.jpgPicture BU Lights.jpg
Picture with both BU and Brake.jpgPicture with Brakes.jpgPlain Picture Installed.jpg

I also mounted a RAM mount for my phone, pretty functional low key thing.
Ram Mount.jpg

Now I am ready for some spring cruising!

[F500guy]

Since there are a few on the forum that are enjoying playing with their carbs, thought it would be fun to share info. Since this is my first time to really play with a big engine like this, I am really pretty amateurish on this subject, far from an export but enjoying the process. Here is my latest update on my tuning. My next item to work on is the transition for moderate throttle before the secondaries come on line, and along with that do some efficiency tuning. My car runs great, and if I was just driving, I would be happy but since it is a new hobby, always have to tweak something.

Here is my current set up with recent tweaks:
Settings 4.28.2026.jpg

Here is a steady state cruise. I would like to get over 14 for the AFR (14.1 stoic for 10 ethanol) so it is not to bad anyway, but think I can go better by reducing the main jet.
Steady state run.jpg

Current struggle is the 20-50% throttle pulls the AFR high-over 15 when that should be lower like 13 or so. To the best of my knowledge I will need to drill out the Power Valve restrictor. it is a fixed size in the holley and I can try and drill it out or drill and tap it for a 6-32 jet. Then I can adjust the secondary main to compensate for that extra fuel flow thru the power valve. At more than 50% throttle, the AFR climbs back down to a reasonable level.
0-60 run.jpg

Maybe take it to a dyno when I feel mostly done to find the real power number for the AFR. Drives great, accelerates smoothly.