Timing Curve on 360 in an RV

I would still verify your timing marks on your balancer to make sure they are correct. Is the firing order correct? I have the same backfire issue as you have but not until 34-36* so something sounds off on your setup. Have you tried a different coil?

I have mine currently set to have 32* all in at 4K RPM with initial at 18* and 10*vacuum which gives me an actual idle of about 24*. The vacuum numbers will drop some under acceleration depending upon the load on the engine as the ECU is reading the manifold vacuum and compensating accordingly.

I agree that you should be able to run more timing than you currently have without issue. I would raise the rpm for total in and try adding a few * at a time and see what happens. It seems to be all trial and error with this system and I’ll be the first to say I’m not really impressed by the timing control or lack thereof.