I'm in the same boat. I have an EZGO ST350 that had a broken rod when I got it. Pulled the engine and shipped to Motors and More for a rebuild and I bought a replacement carb from them as well since the original one was in bad shape. Got it back and all together and it backfires through the carb. It will actually send flames out of the intake. One thing I noticed is the linkage, which I believe is the governor, over the rear end seems to be sticking and I wonder if that is part of the issue.