Hello,

I'm just curious if you 425 guys can answer this for me. I got a crazy spark plug fouling problem, but its only on by back 2 cylinders on each bank. the front 2 burn perfectly with a light tan spark plug, the back 2 turn completely pitch black.

I've tried adjusting the carb, to no avail, but it doesnt seem like a carb problem to me. Could this be valve seals or something like that? i cant think of any possiblity. I do have an exhaust leak on the back 2 manifold ports on the drivers side but that wouldnt effect both banks would it?

what do the fouled plugs look like?

http://www.partsamerica.com/Auto101PlugCondition.asp

check you wires and cap. sometimes cracked wired or damaged or deteriorated caps can casue the plugs to foul. also do you have stock plugs in it, as in the right heat range? what kind of driving do ya do. start and stop stop?

i can't remember off the top of my head, what is the firing order of the 425?

Hello,

I'm just curious if you 425 guys can answer this for me. I got a crazy spark plug fouling problem, but its only on by back 2 cylinders on each bank. the front 2 burn perfectly with a light tan spark plug, the back 2 turn completely pitch black.

I've tried adjusting the carb, to no avail, but it doesnt seem like a carb problem to me. Could this be valve seals or something like that? i cant think of any possiblity. I do have an exhaust leak on the back 2 manifold ports on the drivers side but that wouldnt effect both banks would it?
Lux hauler has the right idea. Describe the color and smell (scent) of the discolored sparkplugs. Are the discolored plugs dark gray and possibly smell like gasoline or black, dark brown with oily deposits? If it looks and feels like oil? Check the PCV valve (shake it and listen for a good rattle to insure it’s not stuck open) and if it is ok check the transmission vacuum modulator line at its attachment point to the intake manifold for transmission fluid inside the line. If the modulator has failed intake vacuum will draw the transmission fluid from the transmission through the modulators, then the vacuum supply line into the intake manifold and will end up on the nearest plugs. If the inside of this line is wet with transmission fluid change the modulator.

hmmm that transmission line is an interesting suggestion, they are carbon fouled though. the pcv valve is new, as well as the cap, rotor, and wires. i'm stumped

Does the engine misfire? How long after the installation of new plugs until they become fouled? If some type of oil does not foul the plugs then it must be either coolant or fuel and coolant fouling looks completely different on the electrode than fuel. If fuel were the cause of the plug fouling, I would expect the odor of gasoline on the fouled plugs. Do you notice (in the rear view mirror) any black smoke coming from the exhaust when diving?

it only blows black smoke after they foul, and its pretty random. sometimes when its cold, sometimes when i get on it too much, sometimes i'll just drive and itll be fine, i'll shut it off and come back and they'll be fouled. its insane.

it only blows black smoke after they foul, and its pretty random. sometimes when its cold, sometimes when i get on it too much, sometimes i'll just drive and itll be fine, i'll shut it off and come back and they'll be fouled. its insane.
Does the engine still have the original carburetor installed? If so take a flashlight and look down into the secondary side of the carb. Drive the car until the engine is at normal operating temperature. Stop the car, shut off the engine and remove the air-cleaner top. Hold the carburetors air-flap open (the large plate covering the top of the secondarys) and check the top of the throttle-plates for liquid fuel. Continue to watch the tops of the secondary throttle-plates for any signs of fuel dripping from above. If you see fuel dripping on the throttle-plates wait until the engine cools just enough to remove one of the rear sparkplugs that had been fouling (at cylinder 5, 6, 7 or 8). The plug should be wet and smell like fuel.

yes it is in fact the original carb, if that is the case what would i have to do to fix it?

We need to try and pinpoint the cause of the problem? The last thing you want to do is replace a bunch of good working parts because of a misdiagnosis. Based on your posts I get the impression you think the plug fouling is caused by fuel but before you replace any parts don’t you want to know without a doubt it is fuel? Every diagnostic suggestion I have made can be completed in short order. If it proves to be a fuel (carburetor) issue, rebuilding or replacement may prove necessary? If it is the original carburetor, it along with many of the other parts are some twenty-seven years old. I suggest you take just a few minutes and find the exact cause of the problem before replacing any parts. Let me know what you find.

A carb rebuld wuld do godd for sure, I had a similar problem for a while. But, adjusting the fuel-air mix would do good as well. Make sure your timing is good and the idle is right, then twist the screws out untill the highest possible idle is reached. That might cut down a little on the carbon deposits.

yeah it would be really easy and pretty quick to determine like if coolant is leaking. just doa compression test on all the cylinders. or just the problematic ones if you don't want to do all of them. if you don't alreaddy have one just go to a auto parts store and get a compression tester. and someone correct me if i'm wrong but if a head gasket is blown there should be 2 cylinders next to each other with low compression, i think. but one way to read the plugs for coolant would be if they are fairly clean but have an oily film on them then that is coolant. because trust me it isn't fun spending money on stuff then having the smae problem after the new parts are installed.