1st time for my brother and I putting in a new set of pistons and rings on my sled. The carb boots were shot so I replaced those as well. It went good till we tried to start it. It would catch after 2 pulls and die right away. We pulled and pulled but found a flooding problem. Ok so we took out the plugs and pulled , put the plugs back in and same thing only this time it exploded fuel in the exaust pipe. Sounded like a m80 went off in the shop. The sled ran good before I did the top end. I didn't mess with the carbs at all. What am I missing? Thanks for any help.