it is in a 350 carbed with aluminum heads. i am using autolite 3924 plugs. the motor keeps fouling the plugs in cylinders 1,4,6,7. i have new cap and rotor and plug wires. what would make it foul on some plugs and not all of them? i pull them out and they are just covered with carbon build up. i clean them really good, put them back in. and the next time i pull them they look the same again.

I don't have any real insight for your problem, but I can say I have never, never had much luck "cleaning" used spark plugs. No matter if it is a 2 stroke snowmobile engine, lawn mower engine, or a 350. If you replace them with new ones does it immediately foul them? I don't have any experience with Autolite plugs, but with those heads you need a .750 projected tip, gasketed plug. I ran those heads in the past with I believe AC plug FR3LS.

Look closely at your intake manifold; specifically, the routing of the runners.

Notice a clue?

yeah if i replace them it just does it again.


ok they are all 4 feeding from the same side of the carb. could the jets in the carb be dirty? what esle could be wrong?

Ding! ding! ding! ding! ding!

Not dirt in the jets; most likely, that would make it run lean.

More likely, a leak in the bottom of the fuel bowl, a bad intake gasket (across the bottom of a port or 2, so it can suck in oil from the crankcase), etc. Start by looking for a carb problem; too much fuel for whatever reason.

ok i will replace the gaskets first since that will be easier. if that doesn't fix it, do i need a new carb or just a rebuild?

I'd suggest a carb rebuild FIRST.

Check the fuel bowl carefully for cracks.

any other ideas?

Check for a stuck float on one side.

How does it do now that the carb is all repaired and working right, or replaced?

You didn't state what kind of carb you have. If it is a Quadrajet then it is a good possibility that the "k" plugs in the bottom are leaking. There are two small bosses on the bottom side almost centered and they will usually have an aluminum plug in each one. When they start leaking they will literaly sit and drip into the intake. You can flip your carb over and clean them off and J-B Weld them. This was a very common problem "Back in the day".

Read his sig....You're absolutely right about the Q-Jet though; the 4 little bitty spun-in plugs on the features that look like little towers from underneath, below the primary jets, are NOTORIOUS for developing dissimilar-metal electrolysis, which eats through the chinesium casting, and makes a leak. Since those 4 (unlike the 2 larger aluminum ones about the size of a dime under the secondary metering wells) are DIRECTLY exposed to vacuum, they do MORE THAN just drip; the engine literally SUCKS the gas through them. There's more of those exact same things under the accelerator pump, but those are outside the intake, and merely drip gas on the intake.

The 2 larger shiny aluminum ones on the sec side are isolated from intake vacuum by the throttle plate gasket, so they don't really matter.

But he doesn't have a Q-Jet, so it's not the issue.

The Carter carb has 2 fuel bowls, one on each side of the carb; so the float and needle valve thing is a very real possibility. Could also be a cracked casting, "foreign matter" in an air bleed, and so on.

It's clearly a carb problem. See my signature for a helpful mental pointer with troubleshooting. It is particularly helpful in directing one's attention properly when there are multiple symptoms in places that share one common feature: like 4 cyls all fed from 1 side of the carb. Kind of a glaringly obvious, slap-in-the-face kind of diagnosis.

well i tried rebuilding the carb but it still did the same thing. i think that carb is just worn out. so i went on e-bay, and saw this---http://cgi.ebay.com/ebaymotors/HOLLE...em250216370641

it seems like a good deal. it has vac secondaries which i have been told is better for autos. tell me what you guys think about it.

you really want a 650 double pumper but why have such nice aftermarket heads and a tiny tiny cam?

Did you really rebuild the carb? Disassembled the whole thing, soaked everything for 24 hours in real carb cleaner, flushed out every passage with compressed air/aerosol carb cleaner? Replaced every gasket and seal with new ones from a rebuild kit?

Common poor advice. Even Holley says it.

It's a matter of sizing the carb so the combination of engine CID and RPMs doesn't lead to a bog when you go WOT with the DP. With a 350, that's something like 1350 RPMs with a 650 CFM DP. http://www.holley.com/data/TechServi...Carburetor.pdf Even Holley has the right answer if you dig deep enough.

I gotta agree....

Manual secondaries are SOOOO much better, if you can teach your driver how to drive. (not just stomp on the gas to the floor from a stop)

I'd suggest one of these right here. http://cgi.ebay.com/ebaymotors/ws/eB...category=33550 Maybe not this one necessarily, but one like it. List # 4778. Pretty common and easy to find used.