Okay here is the situation. I have a weber on my 258 with no ECM (82 didn't have it). All the emissions stuff is still intact. Original ignition. Mr. Gasket fuel pressure reg.

I am getting a backfire on deceleration from high speeds 45+. The kicker is that if i keep the accelerator depressed slightly it doesn't do it.

Have checked the timing and taken it as high as 12 and as low as 6. Have re-tuned the carb.

Went to O'reily's today and rented their compression tool and going to check that tomorrow night. also picked up a vacuum gauge and going to check for leaks there.

I don't know what else to include. Any thoughts or suggestions?

bump

Okay i just did a vacuum test and it spikes when i let off the gas. goes from 19 to 25 in an instant.

I had the exact same problem once on a 258. I even sent the carb back to Weber. They could not fix it so I threw it in the trash and moved on. Sorry.

Kriss