poop

Hello fellow scooter sadists, fitted a mal…172 taffy pipe and modded head, accelerates fine but will only reach 50 mph in 3rd then cuts for a second does the same in 4th when i get to about 65 i poop my trousers at that point and ease of the throttle just in case it gets all dramatic on me, runnin a standard carb with a 122 main in that came with the kit. Think maybe its fuel starvation or maybe electrical…to be honest though i dunno. Any ideas[:’(] [:’(] [:’(]