I know it is difficult to diagnose a problem via computer but here goes. New crate motor (347) with Pertronix ignition and Holley 650 carb. etc (all new stuff). It cranked right up and ran OK. After getting some other issues taken care of (alignment, brakes, shifter etc) I notice the motorwasrunning rough. When you give it gas and even some at idle, it misses at sputters and will even backfire a little. I thought it was a vacuum leak but cannot find one. I then tried adjusting the timing. When the motor came it was about 10 deg. BDC at idle and 32 deg. at about 3000 rpm. I moved the dist. some and it ran much better but now at idle its about 20 deg at idle and off the scale at 3000. Any ideas where to start. I have never had a Pertronix before so I did not know if there was any adjustment. The motor was run on a dyno and supposedly "adjusted". Thanks for helping us novices out.

 

I'd look for a vacuum leak at the carb base gasket.

 

turn your base timing back down to 12-14, so you'll have 34-36 total. you dont want any more than that on there.

 

+1, sounds like a possible vacuum leak

Also, dump the timing back to the original setting. Those are perfect specs for sbf's.