timing or fuel?

[malibujason79]

I posted this on msd's web site and haven't had a reply yet. Anyone want to give there two cents? thanks jason

I'm working on my 400 sbc and i have a couple questions. My ignition set-up is 8360 distributor, blaster 2 coil, 6al, and 8.5 wires. When i put the engine together i installed the distributor just as it comes from the factory with the 2 heavy silver springs and blue 21 degree bushing. i started the motor brought it up to 3000 rpm and set the timing at 36 degrees. Well what i guess i didn't understand, was that with the factory distributor set-up at 3000 rpm the advance was only 15 degrees and not the 21 degrees, so my total timing was 42 degrees at 4000 rpm.
So this past weekend i installed the black 18 degree bushing, one heavy silver and light silver spring, then set my timing to 36 degrees at 3000 rpm. i also removed the vacuum advance since my cam doesn't give much vacuum. When starting the car cold, i will get a small backfire out of the carb. Could this be caused by a lean or rich condition since ive changed the timing. Also ive tried to check my base timing at idle with a plain jane craftsman timing light and a craftsman dial ( which i know you shouldn't use a dial with this set-up) and at idle i'm showing 23 degrees. Is this something to do with both timing lights? or is my timing curve coming in at idle?

[streetk14]

Jason,
23 degrees at idle sound like too much to me. I'd keep it to 17 or 18 if you can. If you want 36 degrees total, then you should have 18 initial and the 18 degrees of mechanical with the black bushings.

I think I know what your problem is. Your advance curve is probably still advancing at 3000 rpm. You may have read 36 degrees at 3000 rpm, but you likely have 41 degrees at a higher rpm. I'd back the timing off to 17 or 18 at idle and see how it runs. You could also check the timing at a higher rpm to see where the advance really maxes out.

Andy