The problem:
Backfire through the exhaust at about 2000 rpm on the right side only.

The engine:
Freshly built 383. AFR 210 heads, Lunati solid cam, MSD distributor, Crane Hi6 ignition, new plugs and wires. All components are new.

Things I've checked:
Compression on all cylinders is 170 psi. All valves adjusted to spec. Swapped in a known, good HEI (no change). Replaced plug wire on each cylinder, one at a time (no change).

What else could be causing this backfire? :confused:

are the valvesprings matched to the cam? it kind of sounds like valvespring or valve adjustment problems. wierd, it does look like you've checked all the obvious areas. but the description sounds very much like valvetrain issues. one other thing that comes to mind is mech. advance rate. although it would be both sides of the motor (exhaust), i've seen advance rates that are too quick/not quick enough create a "bobble" at a specific lower rpm, such as 2000. it's just a stab in the dark guess, though. good luck with it.

I switched plugs from one side of the engine to the other, and the backfire moved with them. Checked plugs, and one was only firing intermitently. Replaced bad plug; problem solved. graemlins/beers.gif

Kyvox, just curious if they were AC Delco plugs. Myself and others I know have had a LOT of problems recently with AC's failing shortly after installation. I even had one that was leaking between the porcelin where it meets the metal body and no it wasn't dropped or damaged from what I could see. I've since changed brands.

As a matter of fact, they are AC Delco, and I didn't drop this one either. They are one of the plugs that AFR recommends. They also recommend a Champion plug, but I don't know the Champion heat range numbers. For that matter, I don't know the new AC heat range numbers! If I have any more trouble with these, I'll switch to the Champions.

kyvox, sweet, a nice easy fix. wish they all went like that. i used to run ac plugs as well, but never had any problems with them. i have since went to an ngk plug (v power), switched when i changed to a pro action heads, and i like them very well. if you change brands, i would consider them as well.

Kyvox thanks for the reply. That's one more mark against AC plugs in my book. I also put a set in my boat. With only 5 hours on them I sold it to a good friend and first time out showing him the boat we had problems. Turned out to be a bad AC Delco plug. 5 hours is all it lasted before it began misfiring. He's had problems with them as well in his vehicles he told me and I've had a few problems with them recently. I'm not sure why all the sudden AC is having quality problems like this, or perhaps it's just bad luck?