Thread: Random Plug Fouling After Engine is shut Off..??

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Ok This one has Me really Stumped!!!, After awhile when the Engine is shut off (Will be running fine before then) then say maybe few Hours Later when I go out to start it I've lost a Cylinder, this has been an Ongoing Saga for about 6 months now, I look at the plug and it's Fuel fouled. (Random Plugs, some wetter then others)
The Engine is a 347 Stroker.

1.Probe Aluminium Pistons
2.Speed Demon Carb (750 Factory Jetted 76/83)
3.TrickFlow Twisted Wedge Heads (Stock)
4.Victor Jr. Intake
5. Camshaft Duration is 224° Intake and 232° with 542/563 Lift.

O yea and this only happends after it is restarted, never happends while just going down the road, The Engine is Brand New will all new Electronics MSD Billet Dist, etc,etc... My only thought is maybe too cold a Spark Plug..?? Carb Baseplate Leaking Fuel then Hot soaking..?? I went 1 up From what TrickFlow Recommends on Heat Range for the spark plugs.
Any help or Suggestions Will be Greatly Appreciated..!!!

Don't know for sure, but it might be leakdown on shutoff due to either a float slight too high or excessive pressure in the fuel lines. What fuel pump and pressure are you running? Just some thoughts.

I have a Holley Blue Going Through a Aeromotive Adjustable Fuel Pressure Regulator set at 7 lb's , I just looked at the Bowl Sight Glasses This morning and they are at the same level (Middle Hash Mark) as last night, The Plugs are Autolite 3924's gapped at .060 this isn't an every day problem just maybe once a week and every day it will sorta miss kinda like a weak fire then after it warms up it clears up and runs great..!! been then just some times the plug remains dead and it won't ever clear up.
Daniel

I just had the same problem on my chevy and found out my carb float valve was set to high letting fuel dump onto my plugs which would get real wet and not fire. Fixed the float and it;s worked fine.

Hmmm...... Intresting Yea I think that's called "Fuel Creep" Which The Regulator is suppose to prevent that, I've set the Floats to Barry Grant's Recommendations at the middle hash mark which is what it calls for in the Manual, Maybe it's loading up at idle and all that atomized fuel is adhering to the plug (s) when the piston is at tdc after the engine is off and the plugs being colder than normal is not burning off Excess Fuel, (Not real sure of what heat range I need) Who Knows this is getting kinda Frustrating, But Thanx For the Input Duane..

I know this thread is old but I'm having the same problem with my SBC.. Ever solve this problem? I seem to have a problem with No.2 only (at front of block).

Its very frustrating having to clean the plug every few days.

Thanks

You've probably got oil coming down the valve guides after you shut the motor down. SBC's are notorious for this.

You've probably got oil coming down the valve guides after you shut the motor down. SBC's are notorious for this.

Hmm.. Is this a common problem for worn out valve guides? My heads are new. Is there any way of checking the valve guides without pulling the head off?

Thanks for the reply

Any suggestions for what I should do to cancel out possible causes would be welcome..

Thanks again

Do a leak down check on the engine. A leak down test makes it very easy to isolate the problem. If it's bad rings, you'll hear air going in the pan, bad guides, air will be going into the valve covers.....

There isn't an easy test for the valve guides. You have to pull the valves and use a micrometer and snap guage to measure the clearances.

Thanks for all the replys.. I will perform a leakdown test first and see if there is anything unusual. The other checkups might not be a job for myself so I may need to seek professional assistance.

I tried swapping the plug with one from another cylinder with no luck. I have also tried running the engine a bit warmer recently because the plugs are a bit sooty. If this does not work I will go to a hotter range.

The carb is a 750 HP DP Holley, the engine is 409cid making 500hp and 500ft/lbs so I think the carb might be ok.

Thanks heaps!

Try reducing the fuel pressure. Or shut the pump off a few seconds before shutting off the engine. A nuisance, but it'll show you if the pump's the problem.

i forgot where i saw them but i saw ignition switches that had a timer circuit built in them to cut fuel off and then cut the ignition at [set time] later... i think they were in summit for drag cars