The Stovebolt Site Forums The Shop Area Engine Shop brand new spark plugs fouling - please help

Anyone know what might be making my spark plugs foul after 10 miles? they are AC DELCO hot 45's.....In case any of you are following, this is the same "newly rebuilt" engine that I put back in my truck in June....here it is October, and the &*^$% thing is still missing so bad I can't dri8ve it. Only missing on acceleration. Ran perfect last weekend after the mechanic set the timing, points, carb, etc....8 miles later on the new plugs, and they are fouled....any help appreciated

Coil may be on its way out, are could be connected wrong. Look at the coil and see the wire going to the distributor should be - I believe.

why would the coil be responsible for fouling plugs with carbon? the coil is 6 months old.

check in this order
-Float setting
-is the accelerator pump working correctly, you check this by moving the carb linkage, with the engine off and looking down the carb and see if if you see a shot of gas
-Manual choke, is the cable adjusted correctly, is the choke fully open when the choke cable on the dash is pushed all the way in.

-incorrectly adjusted float will cause a flooding condition
bad accelaeror pump will cause a miss/hesitation on acceleration
incoreclty adjusted choke will cause a rich condition

R45 should be the correct heat range

This would be a longshot on a rebuilt engine, but could it be possible that your PCV valve is stuck open? I had one stick on me many years ago and the symptoms are identical to what you are describing.

Is your ignition 6 or 12 volt?

OK, I can sure check all that stuff out - the choke problem is interesting....I just installed a new manifold a couple days ago. I have notice that when Installed the carb back on, the choke cable is hard as heck to push in or pull out and out of adjustment. I thought nothing of it as it idles fine in the driveway. I dont really need to choke to start in summer time. I'll also take a look at the PCV valve this afternoon. AS for the carb float adjustment, I just did this right before I put the carb back on, cause the gas was overflowing the bowl/pump before that. The carb pump is shooting gas just fine. The truck is converted to 12 volt. Sounds like my problem is being cause by excessive gas NOT burnt, or excessive gas thta IS getting burnt...which one?

On the coil question, negative side of the coil should be connected to the distributor. Reverse polarity at the coil causes a weaker spark at the plugs. Most noticeable when starting, and also as a miss under load, such as acceleration.

John

dublenaught,

In regards to the 'mechanic' that did all the tune up work....can't he diagnose and fix this problem?

Stuart

You're right. I should take the truck back to the mechanic. This guy just works on older cars. He's very knowledgable. I cant believe he would let me leave his shop with the coil wired incorrectly to the distributor, but that certainally is an option. Again, fouled plugs result from what - too much gas?

dublenaught,

Excess fuel can foul plugs, but usually they will just get sooty (dry soot) and keep going. If the ignition is weak, and the amount of gas too much, the plugs can be overcome and misfire.

Much more prevalent would be oil fouling. This will result in a wet, slightly oily plug, and it doesn't take a whole lot to short the plug out.

As you increase the load on the engine, cylinder pressures increase, and it makes it more difficult for the spark to jump the gap. If your rig is only missing under a moderate load, the first thing to check would be the ignition system.

Under load, engine vacuum drops and the power valve opens to give the engine a little extra fuel. This extra fuel could be enough to complicate a weak ignition.

Find a hill nearby and drive the truck up it, trying to maintain a steady speed without downshifting or abrupt throttle changes. Note when or if it starts to miss, and if it does it consistently.

Your mechanic should be able to read the plugs and interpret what they indicate. If they actually are fouling, they will be dry & sooty, wet & sooty or just plain wet & oily.

A ignition system in good shape will fire through all but the worst conditions inside the engine. Good luck.

Stuart

You didn't say what engine or carb. you have but if it,s a Roch. model B make sure the gasket under the carb has a passageway from the vacuum hole in the base to the intake manifold. Check the power valve in the carb. The piston should should work up & down freely & the ball should cover the hole when the piton is up. If it's black carbon you are getting on the plugs it's got to be over fueling. The choke plate must be vertical after warm up.