One year ago I've bought a 1989 Riga Mini moped with overhauled engine. It's 2-stroke 50 shifty with electronic ignition. Engine model is V501M, produced in Latvia.
The moped starts and runs great, but after apprx. 4 km it runs weaker and weaker and then refuses to start or run.
Next day everything is the same: starts great but after 4 km dies.
What can this be? There is a spark, the fuel gets in, the spark plug is not fouled.