Me and my friend have put together an 80cc MB, and for a day or two it was running great, then it stopped starting, so we tested for spark and had nothing, replaced it with an ngk and it was running perfect again. The day after replacing the spark plug and after riding about a little we were having problems again, it was misfiring badly and after riding about 30m it stopped. We tried for another 5 or 10 mins to start it but it wasn't happening, so we walked it home. We got home about 15 minutes later and after a couple attempts it started, at first still misfiring a little but then it went away and was back to normal. Now 2 days later we are having the same problem with no spark, it misfired a bunch, enough to move you before stopping but now not much, occasionally it fires once or twice but won't start. Any ideas?