I put a standard stock center mount 66/80cc 2 stroke china girl kit on my mountain bike. It ran great for many months until the needle bearing broke and parts of it went through the piston/cylinder and out the exhaust pipe. I bought a new china girl 66/80cc slant head replacement engine. I replaced the head acorn nuts with lock nuts from my local hardware store, mixed up a gallon of gas at 20x1 dino oil and fired it up. It was running fine as I broke it in. I went through the first tank no problems. I never gave it full throttle. I poured the rest of the gas mix into the tank and kept breaking it in driving it a little bit every day for short rides, gradually giving it more throttle and going full throttle for short bursts. When it got to about 1/4 tank gas left the engine stopped and wouldn't start. It was clear it was losing compression because I could feel the air against my leg as it shot out from around the head every time I popped the clutch. I figured out that the lock nuts I got for the head were not screwing down far enough on the studs. They would screw on a little bit but then would get locked on the studs until tightening them just turned the entire stud. I removed them before I stripped out the stud's threads or the threads on the bottom. I tried regular non-lock nuts and was able to get some that would screw down on the stud threads but no matter how tight I screwed them down the head kept leaking air. I replaced the head gasket with the one from my old engine and tried it again. Result: It started up but would bog down losing all its power every time I popped the clutch also smoking like crazy, oil dripping out of the exhaust pipe as it cooled. I ordered two new stock NT carbs (BGF $12 each) and two new head gaskets (dax). I also got a new spark plug (dax). I emptied the gas tank and cleaned it out with straight gas and drained it again. I mixed a gallon of gas at 32x1 with Castor 927 racing oil. I put one of the new carbs on and put one of the head gaskets on the head and made sure the head was tight with a decent amount of torque. I screwed in the new spark plug, refilled the gas tank with my new mix and tried to start it again. Result: It will only start and run when I have it choked all the way. It bogs down, losses all it's power, and dies when I pop the clutch. It's not smoking like crazy anymore though. When I twist the throttle and then release it revs up high but doesn't rev back down very quickly, it comes down but very slowly. It just seems unresponsive coming down, Turning the idle screw counter-clockwise to lower the RPMs makes it die.
Questions: Why am I losing all its power when I put a load on it? Is this still a compression problem with the head or maybe somewhere else? A carb leak or some kind of other air leak? How can I test? Could the throttle controls need adjustment? It seems like the fuel/air mixture is wrong. Should I adjust the carb needle setting or jet? Is the engine broken in now? Did I break it in wrong?
No wonder so many people give this up and get moped or a motorcycle instead. All advice welcome.
Questions: Why am I losing all its power when I put a load on it? Is this still a compression problem with the head or maybe somewhere else? A carb leak or some kind of other air leak? How can I test? Could the throttle controls need adjustment? It seems like the fuel/air mixture is wrong. Should I adjust the carb needle setting or jet? Is the engine broken in now? Did I break it in wrong?
No wonder so many people give this up and get moped or a motorcycle instead. All advice welcome.