Engine & Exhaust / Q&A / Tech

Mailbag: Leaning Out a Rich Condition

leaning out a rich condition

J.S. • Saltillo, MS
Q: I have some questions concerning my 1981 GMC 1/2 ton truck. It has a 350 that’s bored .040 inches over with flat top pistons, ported and polished LT1 heads, a Lunati Bracket Master II cam, and an Edelbrock RPM intake topped with a Carter AFB 600 cfm carb. This combination runs way too rich and fouls out the spark plugs almost monthly. What heat range plugs should I use to fix this? I’m currently using NGK YR5 plugs. Is there any other way I can get my truck to run leaner?

A: It’s very common for a high performance cylinder head and cam combination to run rich. First, you can rule out your current spark plugs. The NGK YR5s will operate fine with your setup. Try fine-tuning your carburetor’s jets and metering rods. If that doesn’t lean things out, then upgrade to an ignition box with a higher spark. It’ll help burn excess fuel at low speed so the plugs won’t foul.



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