I put a fuel pressure gauge on my 78 L82 quadrajet.. Temporary install with gauge taped to the end of the hood so I could see it while driving. At warm idle and at all speeds the gauge rapidly fluctuates between 5 and 7 PSI.

I attribute thee rapid fluctuations to the lever action of the fuel pump. It is an aftermarket fuel pump but I don’t know what kind of.

I have been fighting a rich condition for a long time.

Could it be that even though it stays below 7 psi the hammering of the pressure could be overtaking the needles and putting excess fuel in?

car is now in storage and rear end out of it including exhaust system so I can’t do much testing but I strongly think I need to install a fuel pressure regulator.

Thoughts?

 

Is it the original carburetor for a 78 Corvette?
How are you determining it's rich?
What is your initial timing set to with vacuum advance disconnected?
What spark plugs are you using?
Have you tested the resistance of your plug wires?
7 psi is not excessive.

 

Thanks Mel. All items I have addressed for some time. I plan to start another thread when I get the car back together and on the ground. Waiting for rebuilt trailing arms and differential. I thought I might just question the fuel pressure for something to do while I wait.

when I checked the fuel pressure and it bounced between 5 and seven my first thought was I did not find a solution. But thinking maybe the rapid bouncing is a problem.

Spark plugs are black and fouled. I forget but I think the plugs are ac?? Gapped at 45. Whatever is stock is what I put in. Along with new plug wire, rotor and dust cap.

I had it set at 36 btdc w/o advance. Took it to a specialist and he could not improve it so he put a different carb from what appears to be a different 78 corvette. Said is was better. It runs worse and yes I am pissed off about this and he no longer has my carb and I won’t go back there again.

Why rich? Plugs are black and sooty. Car smells awful. If I drive it into the warehouse everyone complains. I have not looked down the carb when running to look for leaking gas.

I appreciate your questions and help. For now I was just wondering what others thought about the rapidly fluctuating pressure gauge and if I might consider a regulator.

I hope this does not come off as wasting anybody’s time!

 

The SOB took your rare 800 cfm L82 carb and put a different carb on it that doesn't run well...? I would demand that he give you the original carb back, and then punch him right in the nose.

 

Need to know exact plug due to heat range.
Need to know exact carburetor, number is on driver's side listed vertically starting with a 7 or 17.
Are you sure the plugs aren't oil fouled?
Was the idle speed quality effected by turning the mixture screws clockwise?

 

5-7 is pretty normal, you shouldn’t be getting issues with that pressure on a Quadrajet unless it’s going higher than that.

What’s the carb number of the Quadrajet on there now? Do you know the one of the carb on there before?

17058202 Federal emissions no AC
17058204 Federal emissions AC
17058210 L82 no AC
17058228 L82 AC
17058502 California emissions no AC
17058204 California emission AC
17058582 High altitude no AC
17058584 High altitude AC

Edit: These are all 1978 automatic carbs. I just copied and pasted the list from a different thread.

 

Nice chime in Lars bc the 800 cfm you did for me is still on my 78
Not real great for gas mileage but my 78 L-48 does run lake a raped ape!!!
Happy NY............
JJ78

 

November 2024 I replaced the R45TS spark plugs with AC Delco Rapidfire #10 which I am told is a direct replacement. The old plugs and the new ones are gapped at .045". Below is a picture of plugs 1 to 4 and another pic of plugs 5 to 8.
These plugs have maybe 15K miles on them. They have been in storage in a box for over a year.

I also show a picture of the Rapidfire #10 that I pulled from cylinder #1. It probably has less than 1,000 miles on it. The car has not been driven since the beginning of November.- rebuilding trailing arms and differential. That plug looks pretty bad to me.

I can't run the car at this time as the rear end, including exhaust is out of the car. So, I can't get the timing settings.

The carb I used to have was the original #17058211 - casting # from 1976 to 79, Year 1978, Federal, Chevy and manual transmission. I have no idea WTF I have on there now. Even I can tell this is a Frankenstein job. Nor a good relationship anymore with CC. I guess the best I can hope for is this carburetor will work. I am pissed off and I have asked them to find me an unmolested carb for a 78 chevy but I don't have too much hope of getting anything from them.

Any comments of the plugs as to what they might tell us is great. I started this thread really only questioning the fuel pressure and I was going to install a fuel pressure regulator while I wait for reaer end parts. Based on everyone's help I will not be doing that.

My rear end parts should be coming in soon but I will be laid up for a while with cataract surgurey so I probably will not be able to do much with my car in January. Once the rear end job is complete I plan to attack the engine and will start a separate thread .

Thanks all.

Jim

 

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Perhaps fluid-filled gage would not jump so much ?

 

#17058211 would be an original for a 4spd L82 in 1978.

 

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It looks like you now have a 17058228, or a 1978 L82 automatic carb. It should have the same 77/53 jet/rod combo and be set up very similarly everywhere else. If gone through and set up correctly it should be able to work just as well as the carb you had on there before.

Your timing is pretty good being 36 total, but running more advance at idle by plugging your vacuum advance into a manifold (has vacuum at idle) source should help keep the plugs cleaner. Right now it’s plugged into a ported source on the front of the carb.