I just rebuilt one of those mothers! I had similar problems. With luck you may just have something loose in there that needs to be properly torqued down to proper specs. If you are not somewhat experienced mechanically or naturally bright, it takes patience and thinking to get it right. You seriously need a manual. Go to Moped riders association site therein they have complete manuals online, can you believe it? Some of the threads are left-hand and you need to know which ones are. Also you will need to use an oil filter wrench to hold one of the parts while you torque something to specs. Look over the repair manual and assess whether the job is for you or have it done outside.
Best of success!!!!!!!!