yama qt50 mystery in RI

Joseph Lisi Iii /

I'm currently working on a yamaha qt 50 and it's driving me crazy. I't seems to be getting gas and compression along with a powerfull if not incredibly consistant spark. By that I mean that the plug usually sparks when grounded to the head on the head on the outside, but every time I actually install the sparkplug and try to start tie bike (kick start, very annoying) nothing happends, not even when I use starting fluid with the carburator off of the manifold. Then when I pull the plug out, it won't spark, for a while, until I dry it thuroughly. I have considered a flooding issue, but I think using starting fluid and bypassing the carb compleatly has eliminated that possibility. I strengthened the spark by taking a piece out of the spark resistor and replacing it with aluminum (big spark). Does anyont think it could be a timing issue, it's the only part of the bike I haven't taken apart (no puller). I don't think it has points but it may have a timing plate. The most frusterating thing is the bike ran for a few minuits and died never to start again. thanss

Re: yama qt50 mystery in RI

See Ya Moped Army /

Maybe a bad CDI unit?

Re: yama qt50 mystery in RI

they didn't have cdi... atleast i don't think. I have a qt50. Try cleaning/decarbonizing your exhaust, if it's clogged the gasses can't escape and the motor won't run. Put the exhaust in a fire, and let it burn. But don't let ir get red hot, then it'll start to melt!

Re: yama qt50 mystery in RI

See Ya Moped Army /

If it doesn't have points and a condensor, it has a CDI ignition.

Re: yama qt50 mystery in RI

Sure looks like a basic ignition problem.. like maybe the spark is grounding before it gets to the plug's electrodes.. or something as simple as a wrong gap on that plug.. Dirt and carbon easily conduct high voltage electricity.

I'd clean everything and use a new plug and a substitute another coil / ignition wire temporarily . If it runs with another coil and a new plug, the plug's wire or boot or something could be leaking or broken.. The coil itself is no doubt ok.

When Starter Fluid doesn't fire up it's because there's no spark. Timing and carburation and even compression are pretty much irrelevant.

Re: yama qt50 mystery in RI

Dave Peterson /

I had a simular problem with my Qt50. My Yamaha parts guy let me take home a new CDI unit to test. The new CDI did not help. I pulled the flywheel and found a broken wire. It might be time to pull the flywheel. Skipjaz

Re: yama qt50 mystery in RI

Joseph Lisi Iii /

thanks fellas I'll check back in tomorrow

Re: yama qt50 mystery in RI

Paul Bartliff /

Hi. from experince I would definatley fit a new plug first or even if it is new fit another. We race two strokes and plugs can be faulty out of the box. Good luck. Paul

Re: yama qt50 mystery in RI

Joseph Lisi Iii /

Still nothing. I've removed the flywheel and everything looked fine, and non adjustable.It's so wierd some times it has a strong spark sometimes a weak spark and sometimes no spark, but it hasn't started since the first time I drove it around my drive way.I don't see what could have broken, especially not in the electrical system. All of the connections are clean the on off switch looks clean, I removed the keyed switch for now, and I'm all out of ideas. Mabey a wire has broken inside of it's insulation, but I don't see why or how, and I really don't want to rewire this bike from scratch and find out it wasn't the problem.Sheesh!!!

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