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I took my buddy for a ride yesterday and the big block had a miss in either the number 2, 4, 6 or 8 cylinder. It started happening halfway through our drive, driving at a constant 60mph @ 2500RPMs it started popping. We pulled off to the side of the road and looked things over. We thought of a couple ideas (out of time, rocker out of adjustment, fouled plug, arching spark some how). Well on the ride home it was doing it most of the way so I pushed in the clutch and revved it up a little bit and the popping out of the passenger's side exhaust stopped, after about 5 minutes of driving at 60mph it came back again. I dropped it down to third and gave it to the big block and it pulled hard like it normally did. After that little run the popping went away again.
Got back to the garage and pulled all the plugs. The plugs are black as can be...it's not oil, it's a dry powdery black build-up. I'm thinking the carburetor is running way rich and is fouling the plugs at low RPMs. What do you guys think?
QuickVet:
I'm running the stock jets and power valve for the carburetor. The primary main jets are 80s, the secondary main jets are 78s and the power valve is a 65. Do you think I need to de-jet the primaries?
Chris:
I checked all the plug wires and they all seem ok. The distributor is the stock one out of my 350, do you think it's maybe not getting enough spark? In the very near future I will be getting an MSD 6AL Ignition Box.
Yea Shane, you've probably fouled a plug or two. My 427 used to do the exact same thing. It would run good for a few months, then a plug would foul, the idle speed would drop, and it would run rough. I would put a new set of plugs in to fix it. It finally went away after I recurved the distributor using Lars' kit.
In a nutshell, you're out of tune. A rich carb or incorrect ignition curve could be the cause.