I have a b18c1 boosted with precision 660cc injectors and a 57 trim on e85. I have started the baseman and I can get it to idle right afr and rev to 3k or so. But if I tap the gas idling it goes max lean coming back down from rpms. And decel goes max lean as well and backfires badly.

 

It's supposed to be lean on decel. It will be driving as well. If you keep injecting fuel on decel you wouldn't be able to engine brake and what not and that extra fuel would pop and backfire in your exhaust

 

Try adding some timing in the decel areas of your timing map to get rid of backfires.

 

Look at your data and see if you are coming out of fuel cut on decel. Off throttle fueling will cause bucking and backfiring, and can cause high exhaust temps too. Adjust your fuel cut MAP threshold as needed to keep it activated while coasting.