[MidnightAuto]

I’ve been trying to dial in my carb a bit after adding 1i ch spacers under all 3 of them. Car ran great but the A/f was a little volatile fluctuating 2-6 points. Over the last week the car has started to run poorly. Here are the specific symptoms:

Idle a/f is good at 13 with 11 vacuum at 740 rpm. Low rpm cruise (1200-1900) with 16 vacuum is runs fine, fluctuates between 12 and 14 a/ff. When I slowly move up rpm (2000-2500) vacuum drops to 8 and a/f goes to 16-17. Car runs bad hesitating, light back fire/miss, etc.

Dick b was helping me troubleshoot the carb, it is a new rebuild and has run great for last year. But as we dove into, all the carb checks seem fine. So I am starting to think it’s something else.

What would cause a lean condition as vacuum drops?

Timing is initial 17 and total of 36.

I do have a petronix 2, but have never had any issues with it. Not sure how I would trouble shoot that to begin with.

Thoughts

[steve25]

Since at that rpm ( 2500) your still running just on the center carb my first guess is at that rpm the carb is starting to run out of fuel as in

Clogged fuel filter.

Fuel pump going bad.

Dry rotted or poor fuel line hose connection allowing the pump to suck air and not fuel.

Carb float hanging up.

Power valve in the fuel bowl of the carb hanging up.

If your mixture is going lean you can rule out a ignition issue because if the cylinders where not firing then you would see a rich condition showing up.

Question, why are you stuffing 1 inch spacers under the carbs?

[GtoFM]

OK, I'm not skilled in a/f ratio, but if the problem started after spacers were installed, start there. Dick B. may have already suggested to blank off the end carbs at the manifold and ck results. Yes, as steve25 stated, you're only running on the center carb, but if the end card throttle bodies and blade seals were disturbed, air intake leakage may result affecting the a/f ratio. Next step, put it back as it was w/o spacers and ck results. My $.02.

[Half-Inch Stud]

Remove the middle spacer and see if problem goes away. If problem stays, remove outer spacers and go figure. Too close to the hood?

[MidnightAuto]

Thanks guys. I’ve got a confluence of issues over the last month and I may have got things out of order. After the spacers were added the car ran fantastic. After some period of time I noticed the lean symptom I described. The car progressively started to run worse to where is was almost not driveable. At that point, I figured out the front carb was dumping fuel at
Idle. That issue ended up being a bad float I fixed. After that is when I asked for help above. Let me troubleshoot some of this and I’ll be back. Ty…

[steve25]

A quick way to confirm that the float and needle and seat are working right in that carb is to blow into the fuel inlet with your mouth.

With the carb in a normal vertical position you will hear your breath entering the bowl, with the carb upside down you should not.

Note that this test does not guarantee that the float is not bad and absorbing fuel when it’s present in the bowl.

[geeteeohguy]

What Steve said. Something occurred to give you a lean condition at cruise. Either not enough fuel, or a vacuum leak. Not an ignition issue.

[MidnightAuto]

well I may be at wits end. I've gone through a lot of ups and downs with my setup over the last two months and it all started with this thread around the lean condition. Along the way, different issues manifested that I wont get into here, but I have made a lot of upgrades and simplified things to where I don't know what to trouble shoot next. Here is what has been done:

tested 3 different center carbs (different venturis), different jets and power valves. checked floats and needle/seat. confirmed accelerator pumps are good
Added a fuel pressure gauge, robbmc pump, 1/2 fuel line, regulator, 1/2 pickup and return vapor line
Removed MSD box (encountered a starting problem that removing fixed)
new spark plugs, and fixed a few wire issues
swapped in a new petronix II (had as a backup)
replaced exhaust manifold gaskets (they were leaking)
replaced PCV valve and all line vacuum lines

I think that is it at this point. the car ran the strongest it has ever run at some point in the middle of this, but eventually reverted back to this lean issue. driving under light load (going up hills makes it worse) my afr can jump from 12 to 18 and you can feel a hesitation/loss of power. What am I missing? I am sure this is going to turn out to be some silly thing - but it sure is getting old.

I appreciate all the advice this forum has given me. You guys have helped me make this car better. All Pontiac.

[MidnightAuto]

well I may be at wits end. I've gone through a lot of ups and downs with my setup over the last two months and it all started with this thread around the lean condition. Along the way, different issues manifested that I wont get into here, but I have made a lot of upgrades and simplified things to where I don't know what to trouble shoot next. Here is what has been done:

tested 3 different center carbs (different venturis), different jets and power valves. checked floats and needle/seat. confirmed accelerator pumps are good
Added a fuel pressure gauge, robbmc pump, 1/2 fuel line, regulator, 1/2 pickup and return vapor line
Removed MSD box (encountered a starting problem that removing fixed)
new spark plugs, and fixed a few wire issues
swapped in a new petronix II (had as a backup)
replaced exhaust manifold gaskets (they were leaking)
replaced PCV valve and all line vacuum lines

I think that is it at this point. the car ran the strongest it has ever run at some point in the middle of this, but eventually reverted back to this lean issue. driving under light load (going up hills makes it worse) my afr can jump from 12 to 18 and you can feel a hesitation/loss of power. What am I missing? I am sure this is going to turn out to be some silly thing - but it sure is getting old.

I appreciate all the advice this forum has given me. You guys have helped me make this car better. All Pontiac.

[steve25]

I think at this point after all you have done it’s time to look at over the steel fuel line from the tank to the pump very closely for signs of being pinched off, and if that checks out it’s time to drop the tank and see what the fuel sock looks like.

[MidnightAuto]

Thanks for weighing in steve. Two additional thoughts/points.

On the spacers, the car run fine (actually stronger) after installing them. So I don’t think that is the issue. This ha snappiness over an elongated period of time, so I mix some stuff up on the when/what, but that is correct.

I replaced the fuel pickup and don’t even have a sock on it. I also added a new 1/2 fuel line. I did use the existing stock 5/16 fuel line as a return line now.

Very frustrating overall.

[Cliff R]

Just a couple of things concerning Rochester 2 Jet carbs.

NEVER use a brass float in one. 100 percent of the brass floats we installed here failed. They have been coming out of Taiwan for at least 20 years now, maybe longer than that. They end up leaking a the seams and sinking.

For the large accl pumps the "blue" seals that show up on them are crap. Soft silicone type material from China and they will swell up in this new fuel and eventually cause issues. This may take a few weeks, but it happens.

Personally I would ditch the 1" spacers. I've tested all sorts of spacers on 4bbl intakes and the pain isn't worth the gain 9 times out of 10. Showing the carb or carbs up higher and increasing plenum area may make a few more poinies WAY up near the shift point, but for sure if the spacers aren't fully divided on divided intake you can and will experience distribution issues having one side see too much of the other side of the intake.

With Ram Air and Shaker set-ups IF you have to move the air cleaner lid closer to the carb you LOOSE more power than you ever hoped to gain. Personally and after trying taller intakes, spacers, etc on my own car I went back to the factory intake with no spacer at all, ended all the "drame" and SOB the car ran quicker in the 1/8th mile than with any of the taller/bigger intakes or any type of spacer used on the factory or taller intakes......imagine that........

PS: I stock nitrophyl floats and good accl pumps for those carbs but not much else these days (lack of interest).......

[mgarblik]

This may sound way out in left field, but it's an easy test. Just for fun, remove the vacuum line and plug it for the vacuum advance. Not saying to make this permanent, just for testing. You said you had 17 degrees initial, and 36 degrees total timing. With a stock non-limited vacuum advance, at certain light throttle driving you could be adding 20 degrees of vacuum advance. That gives you possibly 54-56 degrees total advance if you have 17 initial, light centrifugal springs and vacuum all contributing. That will make the engine "feel like it's lean". Worth a quick check. Sounds like you have beat the fuel system to death with good diagnosis and tests. BTW, your exhaust manifold leaks would render your O2 sensor readings worthless. (false lean) You can't get useful O2 readings with ANY exhaust leaks ahead of the sensor, (s). Hope you find the problem.

[shaker455]

Originally Posted by MidnightAuto

I’ve been trying to dial in my carb a bit after adding 1i ch spacers under all 3 of them. Car ran great but the A/f was a little volatile fluctuating 2-6 points. Over the last week the car has started to run poorly. Here are the specific symptoms:

Idle a/f is good at 13 with 11 vacuum at 740 rpm. Low rpm cruise (1200-1900) with 16 vacuum is runs fine, fluctuates between 12 and 14 a/ff. When I slowly move up rpm (2000-2500) vacuum drops to 8 and a/f goes to 16-17. Car runs bad hesitating, light back fire/miss, etc.

Dick b was helping me troubleshoot the carb, it is a new rebuild and has run great for last year. But as we dove into, all the carb checks seem fine. So I am starting to think it’s something else.

What would cause a lean condition as vacuum drops?

Timing is initial 17 and total of 36.

I do have a petronix 2, but have never had any issues with it. Not sure how I would trouble shoot that to begin with.

Thoughts

Dick Bonesake is Top Notch great guy in my Book!
Selfless and always more than happy to help and keep the hobby alive!

I'm sure he had you modify the cluster per your engine specs.

You can test your Pertronix with a good timing light and rev it up to assure it's not doing something crazy.
Also, monintor your fuel pressure.

[MidnightAuto]

Thanks for thoughts guys. Responding to each:

Cliff- I did have one of those ****ty brass floats in an outer carb earlier. As u said it was full and causing crazy nozzle drip. Replaced awhile back. So one more bite that they suck. I may end up pulling the spacers as u suggest, but that would be my ultimate sign of defeat. Going to save that as a last last resort. Mostly cause it did run good with spacers for a few months.

Mgar- I don’t have the vacuum advance hooked up. And yes I am sure the exhaust leaks were wrecking my reading, which made me that much more annoyed when the issue did not go away after fixing.

Shaker- dick is awesome. Very helpful and got me to the point that it’s probably not carb related. Fuel pressure is rock solid- unlike a month ago when it was 0. Input a brand new Petronix in I had on the shelf, but I will check it for sure. Thanks for the reminder.


So I’ll keep at it and let u know where i land.

On an unrelated note, is it normal for a fuel regulator to groan? After running for a bit, all kinds of weird noise coming out of brand new regulator. Put your hand on it and you can feel the periodic groaning. Normal?

[geeteeohguy]

I had an issue like this on a cross country trip in the '80's and it turned out to be a collapsed sock in the fuel tank. blowing the lines would unkink it for a hundred miles or so, before it wadded up again causing starvation problems. I fought it for 2000 plus miles to Yellowstone and back.

[Half-Inch Stud]

Regulator gonna hum when metering some fuel out. I dunno about audible at idle; a bit much being metered? Seems to be a related note.

[geeteeohguy]

Another thought: I have run into cracked rubber lines from the tank to the pump that won't leak fuel but pull in air, causing lean conditions. I think it may be fuel supply issues in the lines from the tank.

[MidnightAuto]

GTOGUY- gave me a thought. When I replaced my sending unit with 1/2 inch from robbmc- the old one did not have a sock on it. I just assumed prior owner removed, as he had gone thru car pretty good. But perhaps it fell off and is floating around and getting sucked into the pu in a weird way?

HIS- this issue existed before moving to new regulator setup, so that is why I think unrelated. It is metering down from 11 to 5 for the tripower.i figured there could be some noise. Just not used to hearing it….

Thanks keeping thoughts coming.

[MidnightAuto]

one thing I can say, with all the testing i have been doing I can change the center carb in about 26 seconds flat. like an indy pit crew. Anyway, i disconnected the return line to see if their was an issue there. no luck. After reaffirming this is not carb related, I put my best carb back on (dick b one). I did notice that my a/f and idle were a little out of whack had too much idle and not enough a/f. resolved that. going to have some drinks this weekend and ponder it more. No salt on ground yet, so have not put her to sleep yet.