Roadracer's #997 build

Bit of a struggle today. My engine has been running really rich - literally makes-my-eyes-water rich - reminds me of watching top fuel! It also runs like s**t over 1500rpm, popping and banging. So today was spent outside trying to figure this all out. I'd tried the mixture screws before.

It's a SBC with Holley 4150 650cfm double pumper. Davis Unified Ignition (DUI) distributor+coil. And I'll preface all this with the fact that although I've run this combo a few times, I'm far from an expert with the inner workings of a 4150. Carbs are complicated :D

I set the float levels to the bottom of the sight holes. While I was checking it all out I found a broken vacuum plug, so hoped that was the root cause.

I put a vacuum gauge on the manifold, and got 18 inches, and then tuned the mixture (to now about 3/4 out) to get 20 inches. I figure that means there are no more vacuum leaks.(valid?) The exhaust is instantly better, now invisible where it was colored when super-rich. When revving it gets grey/black again, like it's still rich at revs. I set the secondary mixture to the same turns as primary (not sure how to set secondary mixture).

I put a timing light on, set to zero so I can read the numbers painted on the balancer (0-40 is marked). I'm at 14-16 at idle, around 35 total. But to get it to 35 is painful. The motor is revving but backfiring regularly, popping and banging like it's at a rev limiter (which I don't have btw).

But the timing numbers seem close, so I'm moving on. The leads are new, and everything is connected ok - correct firing order on the distributor, and going to the correct plugs.

I check the spark plugs (only a couple miles go-karting on them) and they are black of course (see richness above) but not oily or wet. First thought, can plugs get damaged by running very rich? They are Accel 576S, as recommended by.. well I have no idea now, but they seem to be suitable for this DUI HEI. Gaps are all 55, as DUI recommend.

Last thing I check, I get temperatures from each exhaust - ~650º on all 4 outers (1,2,7,8) and ~750º on all 4 inners (3,4,5,6), so I took that as proof there is nothing terribly bad inside motor; e.g. stuck valves, etc. (?)

Note that there is no "horrible" noise when revving, like a bent pushrod, etc. No tapping, no pinging, no metallic anything. To my novice ears it sounds rough and backfiring - so much so that it's hard to drive. But still smooth at idle.

I have a call out to a couple of SBC folks who have been doing this since the sixties, so we'll see what they suggest.

My gut feeling at this point is that it's the distributor, but it's entirely possible I've done something dumb...

Bummer...sorry to hear this..... I won't be much help here, I haven't touched a chevy engine is probably literally 30 years, the last 30 years for me have been SBFs & Mopar engines. If you were having issues with those I may have been able to help. Good luck, keep us posted.

My initial reaction when reading this is .55 gap on the spark plugs seems huge but I don't know anything about DUI ignition so I won't assume anything. Jim

Sounds like possible bad float needle and seat or a possible bad power valve diaphram in the carb. If timing is correct and advances when you rev it, it should be a carb problem. Are the plugs black fluffy fouled or wet oily fouled. A vacuum leak will cause a lean condition and the plugs will be white in color. Make sure the secondary throttle plates aren't stuck open.

I haven’t touched a carb in a few years. Along with what the others have said the only thing I can add is what is your fuel pressure regulator set at?

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Originally Posted by Mastertech5

Sounds like possible bad float needle and seat or a possible bad power valve diaphram in the carb. If timing is correct and advances when you rev it, it should be a carb problem. Are the plugs black fluffy fouled or wet oily fouled. A vacuum leak will cause a lean condition and the plugs will be white in color. Make sure the secondary throttle plates aren't stuck open.

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Thanks! I have a rebuild kit so I’ll take it apart and see what I find. The plugs were like a blackboard, not oily or wet at all. Appreciate the help.

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Originally Posted by JimLev

I haven’t touched a carb in a few years. Along with what the others have said the only thing I can add is what is your fuel pressure regulator set at?

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Yes good point, I should have mentioned. I have a regulator and fuel pressure gauge plumbed in.. it doesn’t go over 6-7psi.

The rich mixture could be caused by something as simple as an improperly set electric choke. If you are just at the go-kart stage and haven’t run the car very long you could have more run time on the plugs under rich conditions than under normal running conditions. The plugs will color as rich and never had a chance to burn off the soot.

Is this a new out of the box 4150? What pre-installation set-up did you do on the carb? Did you adjust the idle transfer port opening on both primaries and secondaries? Should be no more than .04” uncovered or your idle screws will lose authority. Did you set-up the electric choke? My suggestion is always to start by reaffirming your set-up -- both carb and ignition. And be sure that you know the correct firing order as you can get a 4-7 swap cam for a SBC.



What number PV are you using? Rule of thumb is ½ the idle vacuum but must be at least 1.5”/hg less than idle vacuum or it will open during idle and cause a rich mixture.


You stated you set the fuel level where it’s at the bottom of the sight glass (should be 1/3 to ½) – was the carb level? Engine installation and parking spot can have an effect on the carb angle.


What type of manifold are you using – high rise open plenum or dual plane?

Your video of the engine idling in your driveway sounds like your cam has a bit of overlap (lumpy idle) – do you know the LSA on the cam? Big overlap cams are hard to get the idle adjusted.


What is your base timing set at (vacuum advance hose plugged and normal hot idle RPM).


You mentioned backfiring – was that out the carb or the exhaust?

Thanks NAZ. The motor and carb are both bought from guys that said they ran but had zero info on them. So I know very little of internals of either. No info on cam, pv, etc.

I did convert to manual choke and had it wide open. Car was on level ground not driveway. I’ve read both that level should be half way and at bottom of sight plug.. I chose to believe bottom was correct because how could you set 1/2 way up without a sight plug? I figured you could set “just coming out of hole” without a sight hole. Anyway I do have one so I can do either.

Base timing ~15°. Advances up to ~35 without any any vacuum. Backfiring from exhaust. Manifold is performer RPM.

I’ll look into the carb and see what I found. I hadn’t done any setup since it came from a running motor but of course in hindsight that’s only half the battle. Who knows what jets/pv are in there. I never setup the transfer slots.

Base timing and advance are reasonable starting points. Still be aware that 4-7 swap cams are very popular (I run one in mine) so be sure of your firing order.

Note: when you view the fuel level in the sight glass you are actually seeing a higher liquid level than what the jets see due to surface tension. Not much difference between the actual level and the indicated level, but the carb is very sensitive to head pressure of the liquid column in the bowl so it's best to get this adjustment correct to start with. You can change AFR with fuel level as a fine tuning aid once your set-up is close.

If you have converted to a mechanical choke AND it is working properly then that eliminates one possibility of a rich mixture. But what type manifold are you running?

OK, you’re dealing with an unknown carb, one of the most adjustable models on the planet. My advice to start by verifying the set-up is still valid. But since this carb could have been adjusted any number of ways, you should start with disassembling it and recording all the shooter sizes, all jet sizes (including the emulsion jets if so equipped) and air bleeds (if equipped), PV number and if it has more than one PV, the color and position of the accelerator cams, and the secondary linkage type (there are 1:1 ratio linkage and several progressive linkages to choose from), the standard most use on a street car is 40% progressive (primaries 40% open before secondaries start to open). Take your squirter, jet and bleeder sizes and compare them with what the carb came with from Holley. Since you live near sea level, the standard jet sizes should get you close. This will help you determine which 4150 carb you have: https://www.holley.com/blog/post/how...on_carburetor/

Thanks again. Gotcha on the fuel level, makes sense. I'll raise it up a tad.

> But what type manifold are you running?

Edelbrock Performer RPM - a dual plane.

Yeah, I say 4150, but it's actually a Proform 650 upgrade series - which is close to the same but since you asked. I will certainly strip it and see what's inside.

But back to the 4-7 cam.. never heard of that. I'll google. But would it be such a nice smooth idle if I was wrong? I'd assume that firing two cylinders at the wrong time would be very noticeable.

FWIW, the SBF performer intake has a port on the rear of the plenum that I missed when I installed it. This affected 4 of the 8 cylinders and resulted in popping and backfiring. Wasn't on their diagram and being on the rear of the plenum, it was difficult to spot/find particularly with the engine in the car.

Steve

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Originally Posted by FF33rod

FWIW, the SBF performer intake has a port on the rear of the plenum that I missed when I installed it. This affected 4 of the 8 cylinders and resulted in popping and backfiring. Wasn't on their diagram and being on the rear of the plenum, it was difficult to spot/find particularly with the engine in the car.

Steve

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Interesting, thanks, I'll go check. But I'm hoping that seeing 20" vacuum on the manifold meant there were no leaks anywhere.

James, besides being a used carb subject to any number of unknown mods from the previous owner, that carb is assembled from off-shore parts. It's supposed to be a Holley knock-off but you may have trouble finding the jet sizes it came with originally. You could research a genuine Holley (or QFT) model similar to your Chinese carb and that might be a good starting point. But my advice is to sell that carb on Craigslist and purchase a Quick Fuel 4150 carb the appropriate size for your engine. Quick Fuel Technology (a Holley company) is the gold standard for 4150. Holley has a carb sizing calculator you can use to ensure you purchase the correct size.

Whatever you decide, good luck. If you get it dialed in it will work well for you as you have the advantage of living in a state that doesn't see a lot of extreme elevation changes (unless you want to drive up to the Guadalupe Mountains where it will be pig rich if jetted for your hometown).

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Originally Posted by NAZ

James, besides being a used carb subject to any number of unknown mods from the previous owner, that carb is assembled from off-shore parts. It's supposed to be a Holley knock-off but you may have trouble finding the jet sizes it came with originally. You could research a genuine Holley (or QFT) model similar to your Chinese carb and that might be a good starting point. But my advice is to sell that carb on Craigslist and purchase a Quick Fuel 4150 carb the appropriate size for your engine. Quick Fuel Technology (a Holley company) is the gold standard for 4150. Holley has a carb sizing calculator you can use to ensure you purchase the correct size.

Whatever you decide, good luck. If you get it dialed in it will work well for you as you have the advantage of living in a state that doesn't see a lot of extreme elevation changes (unless you want to drive up to the Guadalupe Mountains where it will be pig rich if jetted for your hometown).

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Yep, I'm with you. Since I have it, I'll strip it and use it as a learning experience if nothing else..

Maybe I’ll finally get to use this.. had this for..umm.. almost 30 years now? GT40 was in 1993...

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Fun day.. well I had to do some Honey-Does which was digging holes and concreting in some posts for a new yard project - but then I ran out to the garage to strip/rebuild my carb.

It was interesting. I had a rebuild kit and a LOT of jets, so I hoped I'd find some 85 jets in there or something. Or a hole in the power valve. Something obvious. But no.

The primaries were 66, secondaries 70, the normal 6.5 power valve and a plugged PV out the back. Everything sparkly clean and as it should be. Looked at float valves, replaced most parts I had in rebuild kit, but found nothing untoward. The transfer slots were square - everything I looked at was textbook.

With all the new parts in, did it run better? Did it hell! I reset floats, then set mixture using manifold vacuum (went from 16-20).. and the best vacuum, highest idle, and smoothest running is when the screws are fully screwed in. LOL. Given there are brand new parts now in this, someone must have been messing around with this thing.

The nail in the coffin was that I called the guy I bought it from, and he said "yeah, it's always run rich, and the guy I got it from said the same". So I suspect someone set this up for some drag racing WOT somehow.

So I followed NAZ advice and will keep this for parts, or sell it, and I ordered myself a brand new 793-BR-67212 Brawler Street Carburetor 650 CFM which will be here Wednesday.

Which is my birthday, so Happy Birthday to me :D

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Originally Posted by RoadRacer

Fun day.. well I had to do some Honey-Does which was digging holes and concreting in some posts for a new yard project - but then I ran out to the garage to strip/rebuild my carb.

It was interesting. I had a rebuild kit and a LOT of jets, so I hoped I'd find some 85 jets in there or something. Or a hole in the power valve. Something obvious. But no.

The primaries were 66, secondaries 70, the normal 6.5 power valve and a plugged PV out the back. Everything sparkly clean and as it should be. Looked at float valves, replaced most parts I had in rebuild kit, but found nothing untoward. The transfer slots were square - everything I looked at was textbook.

With all the new parts in, did it run better? Did it hell! I reset floats, then set mixture using manifold vacuum (went from 16-20).. and the best vacuum, highest idle, and smoothest running is when the screws are fully screwed in. LOL. Given there are brand new parts now in this, someone must have been messing around with this thing.

The nail in the coffin was that I called the guy I bought it from, and he said "yeah, it's always run rich, and the guy I got it from said the same". So I suspect someone set this up for some drag racing WOT somehow.

So I followed NAZ advice and will keep this for parts, or sell it, and I ordered myself a brand new 793-BR-67212 Brawler Street Carburetor 650 CFM which will be here Wednesday.

Which is my birthday, so Happy Birthday to me :D

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Happy early B-day James!!

Happy birthday! Like building a house, you now have a solid foundation to work with. One tip, most will tie their vacuum advance hose to the timed spark port and that usually works well. But some engines run better when the full vacuum part is used for the advance. So experiment with both to see which works best in your application.

Thank goodness. The new brawler 650dp showed up, and I installed it today - left it as-is except for swapping the electric choke for my manual setup. Haven't touched mixture, or float, or anything.

Seemed to rev better in the garage, but the real test was 4 laps around the neighborhood. Holy C%%p! Suddenly this thing feels fast. The response when tickling the throttle is instant, loud and I'm sure will be fast. No sign of any misfires/backfires.. all smooth loud power. So happy.. I still wasn't sure this would fix it, and $450 seemed a lot for an experiment, but it paid off.

I'll need a long flat wide road to floor this thing, in very gradual stages. I know we all talk about 300hp in 2000lbs being 6.7lbs/hp (seems about the same as a hellcat) but it's going to fun :D

Haven't done much - more honey-does - but I did adjust the handbrake that was bugging me because it was already almost at full pull. I was thinking I'd have to cut off my crimp and shorten the cable a bit, but when I measured how much I needed to adjust it was just 14mm, so I had that much on the threads. I just had to drop the cable, wind it in and bolt it up again. Now It's just slightly loose with the handbrake off, and starts pulling at tooth 1-2. Gives me more confidence in it :D

As I was going over the registration checklist I realized I had never wired up my horn to a switch, since I'd moved to quick disconnect steering wheel. So I tapped a rubber starter switch into the horn ground wire that comes off the column, and that's now working.

I also wanted to do some wiring troubleshooting. My oil pressure gauge doesn't work at all. I can't see anything on autometer.com on how it works, but I assume that the sender gives varying degrees of resistance depending on pressure? I checked that and the sender is varying from full resistance (i.e. no current) at 0psi to 95 ohms at idle - which is 30-40 psi on my motor. But gauge doesn't move. Perhaps it's the gauge, not the sender, at fault. I'll try emailing/calling FFR/autometer tomorrow. Anyone have ideas there?

The sending unit body is grounded to the engine which is grounded to the chassis. The back of your gauge has a ground connection on it. That wire should show 0 ohms (or very close to it) with your meter connected between the chassis and the oil gauge ground.
The I terminal on the back of the gauge should read 12 volts (to chassis ground) when the key is on.
The last terminal on the back of the gauge is the S terminal, that connects to the oil pressure sending unit, as the resistance of the sending unit changes with oil pressure the current flow to the gauge changes.
Another test would be to check the resistance of the S wire to chassis ground with the engine running to make sure you get a reading.

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Originally Posted by JimLev

Another test would be to check the resistance of the S wire to chassis ground with the engine running to make sure you get a reading.

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Yes all those things check out. The s wire is what I’m saying has 95ohms reading. The feeds all seem correct so it may be the gauge.. I have some questions out to autometer and ffr

Got down to taking some insurance pictures for Robbin at Midwest (amazing experience, highly recommended) - should be covered very soon, and then I can start on registration.

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Will Robbin suggest a valuation for insurance purposes based on their company's experience? Or, will they use your number? Obviously, you know how much you've spent, but your labor is also worth something. The insurable value is then determined by ... ?

The reason I'm asking is because I've been looking for a FF car in just about your level of completion and am curious about insuring it.

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Originally Posted by Lickity-Split

Will Robbin suggest a valuation for insurance purposes based on their company's experience? Or, will they use your number? Obviously, you know how much you've spent, but your labor is also worth something. The insurable value is then determined by ... ?

The reason I'm asking is because I've been looking for a FF car in just about your level of completion and am curious about insuring it.

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Honestly, I didn't ask. I simply gave them a number of what I'd spent - roughly $35k to date, so that's the agreed value. I could have asked for more (labor, etc).. but I didn't. Robbin is super helpful though, you could ask him.

I asked for 6,000-mile policy - pre-Covid I would have gone unlimited, but now I work at home, and therefore don't drive to work!

I thought it was very cheap - ~$450/yr. Definitely my cheapest car to insure.

Step 1 was easy.. went to the county office today and with my insurance cert and $30 I walked out with a 30 day permit. I’m going to use that to drive to alignment, weigh station, inspection etc. no form to fill in or anything..

How’d you make out with the oil pressure gauge?

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Originally Posted by JimLev

How’d you make out with the oil pressure gauge?

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I spoke to autometer about troubleshooting steps - they said to test..

1. that the gauge had 12v between ground and positive - it does
2. that the sender resistance changes between engine off and engine running - it does (likely a bad sender if not)
3. that the gauge shows 100psi when I short between ground and signal - mine doesn't move at all.

He said that if step 3 doesn't work, it's likely a bad gauge.

I send these steps to Dan (via tech@factoryfive.com) - he immediately agreed and put a new gauge in the mail, arriving Saturday. I've had amazing responses from FFR recently - new latch striker plates, new oil gauge, response about shifter boot - they really deserve their top spot in the industry in my opinion.

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Originally Posted by RoadRacer

I spoke to autometer about troubleshooting steps - they said to test..

1. that the gauge had 12v between ground and positive - it does
2. that the sender resistance changes between engine off and engine running - it does (likely a bad sender if not)
3. that the gauge shows 100psi when I short between ground and signal - mine doesn't move at all.

He said that if step 3 doesn't work, it's likely a bad gauge.

I send these steps to Dan (via tech@factoryfive.com) - he immediately agreed and put a new gauge in the mail, arriving Saturday. I've had amazing responses from FFR recently - new latch striker plates, new oil gauge, response about shifter boot - they really deserve their top spot in the industry in my opinion.

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James - What did FFR have to say about the shifter boot? Mine is still on B/O....my last part I'm waiting on.

Jim

James (RoadRacer) did you have an issue with your shifter boot or just didn’t get one?
Mine looks like it is 50 years old.
Good to hear you have a new gauge on the way.

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Originally Posted by 33fromSD

James - What did FFR have to say about the shifter boot? Mine is still on B/O....my last part I'm waiting on.

Jim

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Same thing.. backorder.

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Originally Posted by JimLev

James (RoadRacer) did you have an issue with your shifter boot or just didn’t get one?
Mine looks like it is 50 years old.
Good to hear you have a new gauge on the way.

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No, I just lost mine somewhere along the way. I know I had one! I just won't find it until after I buy a new one. :D

Never posted these, but in case it helps - these are the Gen2-body-on-Gen1-chassis striker plates that I got from FFR - slightly different shape.

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Originally Posted by RoadRacer

Same thing.. backorder.

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Yeah, they said their vendor they were using stopped making them so they are trying to source a new vendor.

My front tires (bought second hand) are bald, so I've been looking out for deals on these: (same tire, obv I'll put new ones on back)

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and this morning I came across this - holy cow that's cheap. Less than half price?! Ok, so they're 2018 but I have no idea how long tires are good for, and trust me, mine won't last long :D

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Originally Posted by NAZ

Happy birthday! Like building a house, you now have a solid foundation to work with. One tip, most will tie their vacuum advance hose to the timed spark port and that usually works well. But some engines run better when the full vacuum part is used for the advance. So experiment with both to see which works best in your application.

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Coming back to this NAZ, my friend who has a lot of experience with SBC/BBC (and has a lot of street/drag cars in his family) said that he disconnects the vacuum completely.. so I will try all three versions of vacuum advance: None, Timed, Manifold.

He also recommended that I installed this kit and use the strongest [UPDATE: weakest!] springs to make the timing curve tighter - he said it'll get to maximum advance much faster (1800rpm rather than 3200rpm) and will be nicer and more responsive to drive.

you want about 12-18 degrees of timing at idle. I would start with about 30-32 degrees fully advanced then adjust from there, if it feels sluggish in higher rpm then add 2-4 degrees


Always happy to hear others opinions.. although of course it depends on motor and I'll be experimenting. Does this sound a reasonable place to start?

You are going to have lots of options there to compare, so it should be fun figuring out what it likes. You may have said it backwards - I believe the weaker springs will allow full advance at a lower rpm.

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Originally Posted by McGuyver

You are going to have lots of options there to compare, so it should be fun figuring out what it likes. You may have said it backwards - I believe the weaker springs will allow full advance at a lower rpm.

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Yes! Thanks. Entirely possible about weaker/stronger.. that was a pure guess. I haven't even opened the package to look yet. :D

Yes, weaker springs will allow a quicker advance.

I finally fitted the alternator, so I can drive around and not worry about my battery lasting. It never let me down go-karting, but now I'm driving around proper, I bolted it up and took my temporary belt to the local store to find the closest fit.

Then I celebrated by driving to fill up with gas (the v2 tank is fast to fill, yay!) and drove around for a bit. Feels VERY ODD to be out and driving this thing. I'll throw the GoPro in there for next time..

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