One fouled plug
Thread Starter
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Laughing Gas
Joined: Aug 2006
Posts: 815
Likes: 4
From: mountaintop, Pa
One fouled plug
Folks,
I have one plug that is dry fouled black. Comp test shows 150psi. The rest look good. Timing light suggests I have spark. I've swaped plugs and wires.
Possible causes???
Cap??
Would the coil cause this?
It's the #5 plug on my 390. Misses at Idle appears to clear up at higher RPMs.
Suggestions?
thanks
bob
I have one plug that is dry fouled black. Comp test shows 150psi. The rest look good. Timing light suggests I have spark. I've swaped plugs and wires.
Possible causes???
Cap??
Would the coil cause this?
It's the #5 plug on my 390. Misses at Idle appears to clear up at higher RPMs.
Suggestions?
thanks
bob
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Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
Originally Posted by Bear 45/70
Bad plug, bad wire, bad valve stem seal or a stuck closed exhaust valve.
I smell Bear Poo, sorry.
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
If it were my motor I would check plug wire resistances, run the plugs thru a pressurized plug tester or replace with new but still test 'em and change the cap. One thing, was a compression test done on all 8?
A intake manifold gasket leak around #5 port under the manifold can't be detected with carb spray and compression check alone.
It would take a long time to get a white lean plug reading holding the throttle up to where it just clears up but worth a try then compare with the other plugs.
A intake manifold gasket leak around #5 port under the manifold can't be detected with carb spray and compression check alone.
It would take a long time to get a white lean plug reading holding the throttle up to where it just clears up but worth a try then compare with the other plugs.
Thread Starter
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Laughing Gas
Joined: Aug 2006
Posts: 815
Likes: 4
From: mountaintop, Pa
On my third plug.
I swapped wires and I'm on my second set. It takes about 5 mins to blacken. It apperas to be getting good spark when I hold it against the block.
Checking for a stuck valve would be?? Pop the valve cover watch the rocker go up down? Spin the pushrods.
My buddy is lending me his IR gun to check temps on the cylinder. The n he suggested I'm spendint ot much time on it and run see what happens.
Also The cylinder held 150psi for 1 hour +.
thanks
bob
I swapped wires and I'm on my second set. It takes about 5 mins to blacken. It apperas to be getting good spark when I hold it against the block.
Checking for a stuck valve would be?? Pop the valve cover watch the rocker go up down? Spin the pushrods.
My buddy is lending me his IR gun to check temps on the cylinder. The n he suggested I'm spendint ot much time on it and run see what happens.
Also The cylinder held 150psi for 1 hour +.
thanks
bob
Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
You have the correct heat range plug for your build?
If that's a yes with your fuel fouling plugs it sounds like a carb problem.
If that's a yes with your fuel fouling plugs it sounds like a carb problem.
Last edited by "Beemer Nut"; Nov 5, 2006 at 08:10 PM.
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Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
Originally Posted by Beemer Nut
You have the correct heat range plug for your build?
If that's a yes with your fuel fouling plugs it sounds like a carb problem.
If that's a yes with your fuel fouling plugs it sounds like a carb problem.
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Post Fiend
Joined: Dec 2003
Posts: 6,658
Likes: 4
From: "Islander"
You check lifter preload on intakee and exhauste on #5?
When hot and running bottoming out just enough to just open a valve off the seat and loose compression but seats on compression check when cooled down a little.
When hot and running bottoming out just enough to just open a valve off the seat and loose compression but seats on compression check when cooled down a little.
Last edited by "Beemer Nut"; Nov 6, 2006 at 12:08 PM.