340 Chugging instead of Reving

Locked distribtor and immediately saw/heard an improvement. Took the rpms I to the 5000 range but got some popping out the exhaust. Changed the timing from 32 thru 38 and the popping stayed. I then watched the timing light while increasing the rpms.and it retarding as the rpms increase. When locked at 34* the timing goes down into the 20s. I believe the only thing that could cause this is the ignition box. Any other thoughts before I ship the box out tomorrow????


And that’s why you don’t lock out a distributor. For one all engines need a curve, however short it may be. And two, ALL ignition boxes retard like that. If you don’t test for it you have no idea how much timing you really have.

6 or more degrees of retard is not uncommon. I think I would lock timing out at 38 for now and start working with the rest of the tune up. IIRC, the plugs looked fat. That can some of the popping you are hearing.