Originally Posted by Buzzfire
Tom thanks for the encouragement. It gets frustrating. I changed the fuel and oil. Mixed brand new oil and fuel. Could I have flooded it? How would I know?
Pull the spark plug and see if it is wet/oily. Dry it off and shut off the fuel petcock at the tank. If you have any kind of carb cleaner or quick start fluid spray just a little into the hole where the plug goes. Put the plug back in and try to start the motor. It might fire and run. If so it was badly flooded. There are many things to check if the engine isn't starting but you said the mechanic got it started so I'll rule out bad ignition or wiring problems. Did you properly gap the spark plug? Start at about .24 to .28 gap. Your gas/oil mix should be between 16 and 24 to 1. That's about six to eight ounces of oil to a gallon of gasoline. If your weather is warm it might not require much choke, start at about 1/2 (choke lever 1/2 way up) or just a little less. Start pedaling and when you're about 10mph release the clutch and slightly twist the throttle. Keep pedalling but don't give it much gas. (don't twist the throttle all the way) If all is right the engine should fire. Most of the 2 strokes take a few moments to warm enough to run with the choke open. Give it 30 seconds at least before moving the choke lever all the way down.
Now let's look at this chain/sprocket problem. Have you done the things that have already been suggested? Check for good alignment from the engine back to the rear wheel sprocket. You don't want much over 3/8" side to side misalignment of the chain. It should be as straight as possible. The tensioner wheel (pulley) must be aligned with the chain. It cannot be twisted so that it is pulling the chain off to one side or the other. The chain tension must be between 1/2" and 1" at the loosest point. The kit supplied chains are notorious for wearing quickly but you haven't riden this bike enough so your chain loosening problem is not wear. Is the engine solidly mounted to the frame. It should not move even when you try to muscle it. Same for the rear wheel and the rear sprocket. Have you closely checked that the rear sprocket is concentric, that is,is it centered on the hub, does it spin true or is there any up/down or side to side wobble? That sprocket installation is very critical to a smooth running chain and one that stays on. You said you have "tightened the sprocket", I assume you mean the one on the rear wheel. How tight are you tightening it? It almost sounds to me as if the sprocket is moving and allowing the chain to loosen then tighten because the sprocket is not staying centered on the wheel hub. Lift the rear wheel off the floor and with the clutch disengaged pedal the bike or spin the rear wheel and watch that sprocket. Anything other than true is going to cause problems. Let's start with all this and come back, let us know how you're doing. We'll get this beast runnin' yet, Buzzfire.