Fouled Plugs (2 out of 8)?

[Jeff Frigo]

I have a fresh 427 center oiler (stroked to 454) with aprox. 1,200 miles on it. It has ported and polished Edelbrock heads and intake. The engine runs fantastic, but fowls plugs number 2 and 6 about every 400 miles. This is a rich fowl, not oil. All of the other plugs are perfectly colored. Did a compression test, all cylinders within 10 psi. No blue or black smoke out of either exhaust pipe. Tried a different carb., same sh*t. My friend says it is due to the dual plane intake, but I don't believe him. 2 Spark plugs every 400 miles is very cheap, but I would like to understand what is going on. Any ideas what is happening, or tests that I could do would be greatly appreciated.


Jeff

[Bob Putnam]

The only things that might effect mixture in two cylinders are a vacuum leak or uneven heat in the intake. Not being an engine guy, I don't know whether the Edelbrock's got any water passages.
A finger "thermometer" on the runners might tell you something, and a can of propane will help locate a vacuum leak.

Frankly, I tend toward oil from the valve guides.

[CobraEd]

how about two marginal plug wires

[JAM1775]

Since you are running steady and strong you probably do not have a vacuum leak but a slight one should "lean" you out mostly instead of fouling you to the fat side. I still agree to check the intake gasket. What if those are the ports tightly sealed while 1/5 have a slight leak? Fix the leak and all four fronts could become fat. Then drop in primary jets.
How are those contacts in your distributor cap ? Are all 8 contacts equally carboned ? Could there be arching in the cap or in the wires ? Pull your carb and check your intake runners. Some dual planes criss cross like my Weaind stealth 1/6, 2/5, 4/7, 3/8 etc. Others may be symmetrical like 2/6. 2/6 may actually be fed by the same jet ! That would be easy if your carb was a bit screwy .Drop one jet size in that one corner to feed 2/6 a bit leaner. With My Weaind both front jets dropped would lean out 1/6/2/5. If 1/5 had a slight leak that could cause my 2/6 to foul down the road because my rich primary jets are compensating for the vacumm leaks in the front ports of the intake . Yes...it happened to me. It took a while to figure out though!

[Leo]

Don't know much about FE engines (and can barely spell FE!) but, what about firing order? Could the 2 and 6 cylinder be cross sparking (poor wires, improper wire routing, graphite dust in the dist. cap) and not firing correctly? I've had this problem with the 5.0/351 firing order. Best of luck!!!

[Pete Wolff]

Jeff,

Did you say polished intake ? I understand that if you polish the intake runners it can cause problems. The rough surfaces found in the intake help keep the fuel and air mixed. I believe that the cylinders you mentioned are close to the carb. Could be that the fuel is falling out of suspension causing a rich condition in those cylinders ?

[Jeff Frigo]

Thank you for all of the suggestions. The wires and cap are good. I have not checked for a vaccumm leak, but if I had one it would lean out those cylinders. I called Edelbrock, they were very helpful, but we really didn't get anywhere. My engine builder just had an operation on his shoulder and won't be back for at least a week. When I talk to him, I will let all of you know what he said. He started building pro-stock engines this year, (actually qualified for 2 races with a 99 Firebird and a driver that never drove a pro-stock car before this year) so it is hard for me to believe he didn't get all of the ports to flow the same, but everybody is human.



Jeff

[427sharpe]

Polished Intake??? Hopefully you didnt polish the inside of the runners---this is a very bad idea because it lets the gas form in 'pools' along the sides of the runner rather than 'tumbling' thru the intake. If you did polish, you can correct it by buying some abrasive rolls (like used to polish metal before buffing) and 'scuffing' up the runners--try to get them as close to the original finish as possible. Good luck!!

[Jeff Frigo]

Guys:


When I say ported and polished, I am not using the exact meaning of the words. This was the terminoligy that was used for many years. Maybe I'm showing my age (only 38), but I should probably say only ported. Thanks for the suggestion anyways.


Jeff

[bkozlow]

Jeff,
It of course sounds like you have an imbalance in your fuel distribution. This has to do with runner lenghts etc. If the engine runs good and you can not solve the problem by staggering the jet sizes to lean out those two cylinders without causing and over lean condition in the other two that are feed by the same primary. I suggest you step up one heat range on those two plugs and try that. This should help your problem.

bkozlow

[CobraEd]

how about a fuel bowl level set too high that drips.