I've been fixing up a Puch Newport that my girlfriend bought. I've done a lot to it so far including cleaning the carb, cleaning and coating the gas tank (which had chunks of rust and also an oil measuring cup in it), cleaning the muffler, and changing the transmission fluid (type F).
What it's doing is two things which I think are seperate problems. It runs great once started but tops out at around 15-20 miles per hour at which point giving it more gas just causes the engine to rev and nothing else. I think it's not shifting right and I have no idea what to do about that.
Second, it won't idle properly. It'll idle for a bit but eventually it dies out. I've tried adjusting the idle screw but it doesn't help. Would giving it a new spark plug help this? It looks like it's still running of it's original.
Any help would be greatly appreciated. I'd like to get this thing finished.