Moped runs fine then slows down, then runs fine after a few minutes?

Hi guys,


I finally have a working moped! It's been great and I'm working on making it look purty, but when I ride it there's something that seems to be off.

I can get it up to around 45mph (it's got a 70cc head), but after a few minutes it refuses to keep the speed and slows down over the next minute; after that, I struggle to keep it above 15mph. However, after a few minutes, it suddenly accelerates back up to like 40mph with no problem.

I have no idea what is causing this. Is it overheating?

Thanks for the advice guys.

Re: Moped runs fine then slows down, then runs fine after a few minutes?

Your gas cap may not be venting causing a partial vacuum in the fuel tank. Can you take it for a ride with the fuel cap off? And, you may want to post this in the REPAIR forum. (edited)

Re: Moped runs fine then slows down, then runs fine after a few minutes?

Love watching people messing with their mopeds....Gas delivery is my guess as well. Could be cap vent...Could be the fuel valve not flowing well. Could be dirty tank clogging your carb. Dirty carb. May need the float adjusted, not allowing enough fuel in the bowl....Have fun!

Re: Moped runs fine then slows down, then runs fine after a few minutes?

♣Slew Foot♣ /

Does the horn buzz all the time and will it only cut out at hi rev?

By pass the horn safety switch

. If you got points. Get a new condenser. Reset the points to spec with a. caliber and probe and testlight.

Un clog the exhaust. Dump gas get new plug with a lower heat.

Re: Moped runs fine then slows down, then runs fine after a few minutes?

if u havent done so,,,do a full rebuild b4 u burn it up.

Re: Moped runs fine then slows down, then runs fine after a few minutes?

I had this problem except I was going 25 instead of 48. Built a new engine and then found a mostly clogged petcock. There were other reasons. This was just the motivation I needed to drop the engine.

Re: Moped runs fine then slows down, then runs fine after a few minutes?

Pushrod Fifty /

I had the same issues on different bikes that were from a bad 1979 condenser and a clogged cap vent.

Re: Moped runs fine then slows down, then runs fine after a few minutes?

If neither of these two likely scenarios pan out also check the float bowl for dirt. If you eliminate spark and fuel then the attention should turn to crank seals likely the flywheel side. The clutch side would give telltale smoke as the clutch oil would seep in and burn

« Go to Topics — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account