I would like to get some ideas on this fouling problem that I have. A little history first this 350 crate motor is new, under 3000 miles; every part on it is new. It has the Edelbrock RPM heads and intake, 750 Holley carb, Xtreme energy Comp Cam and a Pertronix HEI distributor with the Accell Super coil. Here is my problem when I put a new set of spark plugs in “Champion RC12YC” the car runs perfect for about a one tank of gas. Then it starts to foul out usually around 3 to 4 thousand rpm’s it will start to miss fire. Then it will still run but rough, until eventually it won’t idle anymore. From that point I pull the plugs clean them up and the cycle starts all over. Now when I pull the spark plugs they are filled with carbon which can mean poor spark, to much fuel “carb not jetted right” or the carb is not breathing right bad PVC or breather. Since all these parts are new “not saying they couldn’t be bad from the start” it is hard to determine were to start, also anything I might be over looking

 

If you are really sure the fuel mixture is OK, thentry hotter plugs, like RC14YC.

 

I thought about bumping up the heat range on the plugs and the RC14YC would be the next step and I know it’s not a big jump. The RC12YC plugs are the set that Edelbrock recommends for the RPM heads. I talked to the tech guys at Edelbrock they said I could go with a hotter plug but I could risk burning a piston if I go to hot. That is one of my reservations and that I have three sets of the 12 plugs now. My air fuel mix was set to the max vacuum reading.

 

Are you getting a hot spark? what color is the current spark?

 

I should have enough spark with the super coil and the high performance HEI Module, it has a 45,000 max voltage rating. What is the best way to check to see if the spark is hot enough? As far as the plug’s they are black when I pull them out, no oil, just the carbon powder build up.

 

Have you tried a different brand of plug? Champions lost my bussiness years ago because of this same problem. I will use AC, Autolite, NGK or even accel which are Nipon-Denso. The only thing that ever gets Champions in it is my Ducati, but, they cost 10 times as much and get changed every 6k. (Knock on wood now )

 

i will probably buy a set of autolite plug'sthey are the one's that i have used in everything i have owned the only reason i have the champions is because that was what was recomended by Edelbrock when my old man built the motor

 

Update to this problem after going through checking everything that I could check I finally broke down and had a diagnostics done and it ended up being the carburetor I believe it was the blow back valve was bad and it need to be jetted down do to the elevation change. I am having the carb rebuilt right now and I hope this will fix the problem I will let you know.

 

id put delco plugs in it if it was me

 

I went with the Autolight’s. I checked everything I could to make sure it was not a spark issue. After that I talked to a few mechanics they thought mabey I flat spotted the cam I had them run a compression test on it the test came back good he check the carb and it was just dumping fuel. So I will know if rebuilding the carb will work by the weekend.