Just to clarify this is for TWO separate mopeds.
I bought both off craigslist. One needs a new read tire, no big deal, and sputters almost a backfire but not quite. Not sure where to start on diagnosing it, it also smokes a little bit more than the second one which runs smoother. Acceleration is fine, consistent power and rate of acceleration. The noise is less noticable at higher speed but I think its just masked by the louder engine noise.
The second is in excellent shape and runs great when starting cold. After it gets up to full operating temp (about a mile) it starts choking and losing power. I didn't notice the issue during the test drive because it never got up to full temp. The problem was so bad I thought I was going to be peddaling home, stalling if I had to stop and almost completely losing power. The fuel switch (for on, off, reserve) seems loose and probably needs to be replaced. It has plenty of gas, I filled it up with premium 50:1 mix on the previous owner recomendation. Not sure where to start since it could be spark plug, carb, fuel system etc. Hoping I can answer some questions to narrow it down and that its a common enough issue to not have to just start with whats cheapest.
I'm pretty good with mechanics stuff. Any help greatly appreciated.