Im having problems with my timing on my 350. Using my advance timing light I see a variation in the timing at around 2000 rpm. It will vary between 6 and 8 degrees between pulses of the light. Im running an HEI with ACCEL supercoil and module. The vacuum advance is hooked to the highest port on my Holley but the variation is seen with the line unhooked to set initial timing. Is it possible there is a bad bushing or something similiar within the distributor causing a variation like this. It doesnt run like it use to.

You didn't say how many miles you had on the engine, but I have seen a stretched timing chain or worn timing gears cause this, as well as slop in the distributor. I don't think the distributor could cause this much change, but the timing chain could. Does the engine idle seem to oscillate?

the engine idles fine but starts to screw up when revved. I think its also causing an occasional backfire.

it has about 30000 miles on the engine, and about 10000 on the cam. The timing set wasnt replaced when I did the cam because its a double roller and was in good shape. Never sees more than 6200 rpm.

ttt