Tomos Jerky and erratic at startup and low speed

Jon /
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I am hoping someone here might be able to give me a hint as to where I might start the troubleshooting on a recent problem...


Just about finished breaking in moped (460km on Tomos Bullet with biturbo exhaust and 56 jet) so I have been taking it up to higher speeds, once or twice taken it to the max (~65-70km/h) for 20-30 second runs. For the most part still keeping it at 40-50km/h though.

Starting at about 370-400Ks it has been giving me problems at very low speeds just after start-up. The bike starts fine, but for the first few kilometers, especially at low speed (first gear), it seems quite jerky -- feels kind of like the bike is being tugged back intermittently. When I get up to high speeds it runs like a charm though. The power feels great and very smooth.

So this morning, after letting the bike sit over the weekend, I get it started fine as usual, but as soon as I go to take off (about 15 seconds after start-up) it dies on me. This then happens a second time (I filled the gas in the meantime because I thought I might be low). The third time I take off very gently and it goes, but is extremely jerky and just doesn't feel great. I rode around for a couple of minutes but just in case a seizure was about to happen I decided to let it sit and had my wife drive me in this morning. I was going to change the gearbox oil on Sunday but didn't have time -- not sure if I should do this now or if I should just minimize the number of variables that could go wrong.

I've tried to search for posts for similar problems but usually it seems that the power loss is at the top end. Any ideas where I might want to start -- I know I need to check the plug when I get home, although it only has 200km on it so I would be surprised if that is the problem. Maybe a carb/jet problem; maybe clutches; anything else?

Any suggestions about where I should start would be welcome.


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