I completed a build on a Trex bike. I purchased a kit from Motorized Bike Parts. It's an 80 (66) cc kit. The muffler failed the first day. The body of the muffler where it meets the exhaust tube connected to the engine separated. I cannot get the muffler to stay connected to the head. The bolts even 2 on each side come loose. This has caused the exhaust gasket to blow. The spark plug wire connector is a "hokey" thing. It needs to be replaced with a better one. I've tried to find a Z4C spark plug replacement but to no avail. Otherwise the kit seems to be OK. It runs and idles good and seems to have enough power to run 35 mph. I've left a message with Motorized Bike Parts about the muffler...haven't heard back. Are these people reliable? Can you give me any pointers on these comments? Thanks