Jerk and stall when put into gear?

no acceleration, and constant backfires as you try to drive it sounds like it could be tuneup or also accelerator pump in the carb. With the engine turned off, and the air cleaner off, if you operate the trottle, do you see a squirt of gas in the carb? When yo urebuilt the carb, did you make sure all the passages were cleaned out?

I would start with a compression check, then tuneup...