Ah I have a bunch of mobies, they drive me crazy.
-Make sure the carb is pushed ALL the way onto the intake valve, and make sure the little rubber bushing is in there.
-Did you make absolute certain the jet is CLEEEN? Does carb cleaner shoot through it like a squirt gun?
-Mobies have a completely movable cam, which means it is completely easy to mess up your timing. and you need a special puller (mopedwarehouse) to get at it.
-Get the puller, and clean your points, set gap to .12 -.14
still not running well?
-flywheel cap is reverse thread. use puller to loosen cam
-to set the timing on the moby you can use the cigarette paper method. although you will need an asistant.
-remove the spark plug, stick an allen wrench down the hole, and rotate the engine slowly, you want the points to begin to open when the piston is 2mm before TDC (the top)
-stick the cig paper between the points, and have your assistant pull on it slightly (not enough to pull it free)
-get out a ruler with mm, break it, and stick a piece of it between the cylinders heatsink, pointing up next to the spark plug hole.
-as you rotate the engine, the allenwrench should ride up and down next to the ruller,rotate the cam untill the paper comes free at the right time,2mm TDC
-tap it tight with a pipe when you are done, then check it again.
and download this