70s CHEVY 350 CARBON FOULING PLUGS

[jsp282]

Have 77 Chevy 350 W/ Quadrapuke Carb. Keeps Carbon Fouling Plugs In Just A Few Miles. Re-built Carb, 180 Deg Stat, New Spark Plug Wires, New Cap, New Rotor, New Coil, And Oh Yeah, Several Sets Of New Plugs (various Types And Brands). Any Thoughts?

[MagicRat]

Is it fouling due to burning oil?
I know that old Chevy valve stem seals loved to get brittle and let oil seep down the valve stems. New seals might help a lot.

[jsp282]

Originally Posted by MagicRat

Is it fouling due to burning oil?
I know that old Chevy valve stem seals loved to get brittle and let oil seep down the valve stems. New seals might help a lot.

THANKS FOR YOUR REPLY......

THE FOULING IS CARBON NOT OIL. IT'S FROM UNBRUNED GAS AND I CAN'T FIGURE OUT WHY. THE EXHAUST ISN'T BLOWING BLACK SMOKE INDICATING TOO RICH A MIXTURE, BUT THE PLUGS ARE STILL FOULING.

[calgary_redneck]

check the timing if its in spec it will be your carb running to rich most likely adjust your idle mixure and see if it helps. Is it the original q-jet?

[jsp282]

Redneck, thanks for the reply. Regarding the timing. It cannot be set exactly because who ever built the engine didn't put the timing flag on the engine. I've advanced the timing quite a bit. I know this because when the engine is warm, it cranks slowly. The carb is not the original. It is a rebuilt I bought and installed. The truck has had this problem with both the old and rebuilt carbs. I've adjusted the idle jets every which way and it hasn't made a difference.

Something I haven't brought up is that the truck sits and idles alot and it has a mild cam in it. I wonder if it's just loading up when it idles so much.

Thanks again for any help you can provide.

[HDChvyTrk]

What distributor and coil are you running? How much compression does this engine have? Are you sure the plugs are the proper heat range? And did you replace the metering rods and seats when you rebuilt the Q-junk.

[jsp282]

HDChevTrk, thanks for the interest. The distributor is stock (and who knows how old). I did put in a new stock coil. The compression ranges between 140 and 150 psi. Spark plugs are what's called for in the book. Regarding the carb, I just bought a rebuilt (had the same problem with the old carb). Any Ideas?

[HDChvyTrk]

I think I would point the finger at the ignition system. If it is not smoking but fouling plugs quickly I would not think it was enough to rich to matter? I would think about a good coil, like an MSD Blater II and maybe an MSD 5 or 6 series ingnition box. This will help your ignition produce a stronger spark. You may, at some point, want to consider a distributor swap also. I asume when you say " the original distributor" you are refering to a single or dual point distributor. If so, and you want to try and keep this setup you should look at the points, replace and/or gap them. They control coil dwell (charge) time and could be a major part of the problem?? If you have a HEI They are famous for frying modules and you could also check the little nub that sits under the coil that transfers power to the rotor.

[jsp282]

HD, thanks for your thoughts. This motor has HEI ignition and I agree with you, I think it's an ignition problem. I've replaced everything in/on the distributor except the module. If the module is bad, won't that keep the motor from running? Or, will it still run, but perhaps with problems? If this continues, I think I'll just buy a new high performance distributor with a high output coil. When I put fresh plugs in this thing, it runs great! Just can't keep it running for very long! Let me know what you think about that module and perhaps I'll replace that. If it's a go or no go on the module, I'll just get that new distributor. Thanks again for your interest.

[HDChvyTrk]

The module will NOT keep the HEI from operating. It will however kill the timming advance and coil dwell time over 2500 to 3000 rpm. Have you noticed it hesitating or stumbling above 2500 rpm? If it were me I would probably replace the distributor anyway. HEI's are not the best distributor out there, expecially on modified engines.

[jsp282]

Hey again. Interestingly enough, it stumbles and hesitates below 2500 revs. Once above that it really comes alive. The only reason I haven't bought a new distributor is I'm CHEAP! Don't want to spend the $150-$200. Think I'll try a new module and another set of plugs. I'll keep you posted. If you can think of anything else, please give me another holler. Thanks!

[HDChvyTrk]

The, module is cheap abd should be easy to find. The low rpm stumble would make me think the coil was bad? Did you replace that little button under the col when you changed it and/or the distributor cap?

[jsp282]

Hey HD. I did replace the coil and the little nub under it. I talked to a guy at a parts place today and described my problem to him. He said I'm sucking air somewhere. Either the carb base or the intake manifold. So, I'll get some carb cleaner and see if I do have leaks. When I replaced the carb I thought of re-torqing the intake, but just got lazy and put the carb on. I did have a leak at the carb base when I put the new carb on using the gasket they supplied with the carb. I took that off and used the old thick gasket that was on it before. I checked it then and didn't have any carb base leaks. Who knows? I'll do the leak test and let you know. I don't know who you are other than HD, but I want to thank you for all of your interest. My name is Jim and I live is South Carolina. Talk to you soon........

[HDChvyTrk]

Hey jsp282, My name is Chris and I live in central MD. I enjoy helping, if I can, sometimes another perspective can jog the mind and come up with a fix. As for the carb leak, it may cause the stumble but ought to make the engine run lean, not rich? Something I meant to ask, do all the plugs look roughly the smae or are some worse/better then others?

[jsp282]

Hey Chris. You know, I was thinking the same thing about being lean with a leak, but I'll try the leak test again anyway. Regarding the plugs themselves, the plugs on the drivers side front seem to foul first and look the worst. When they foul, the motor starts back firing through both the carb and exhaust. We'll get this figured out eventually huh? Talk to you again, Jim.