qt50 electrics

I apologize for the length of the following post, but your endurance and suggestions would be most appreciated.

Problem: No Spark


I currently have two QT50's, both 1980. The blue one runs great... the red one does not. When I picked up the red one last summer, it ran well for about 30 minutes. Then it started misfiring and eventually, would produce a spark only for one or two of the cycles per kick start. If it ever did startup, it could only run for a few seconds before it lost its spark and died.

Since then I have swapped out about every electrical component from red to blue to see what is broken. Its not the CDI or the coil. I ran resistance tests on the stator and of the four circuits, three of them are a little outside of the nominal range. With this in mind I have been looking for a new stator ever since.

Present Day:

Last night after about a month or two of sitting, I decided to give it another shot. I reattach the stator and other assorted electronics and low and behold it starts up on the center stand and runs like a charm.

Now it gets weird. I want to turn it off so I can put on a jacket and take it around the block, the thumb switch is broken so I turn off the ignition but nothing happens and it keeps on running. At a loss for what to do, I pull the cap off the plug and it turns off (go figure).

Five minutes later I come back with a jacket and shoes, reattach the spark plug and kick it for the next 5 minutes. Nothing happens. I remove the plug and it seems to have gone back to its old ways of not sparking 95% of the time.


I was convinced that it was the stator till last night. I would like to get an impact driver and swap stators to confirm or reject this hypothesis. Since it did run well for a few minutes last night though, I'm not so sure any more.

Not turning off seems to point to a problem maybe in the wiring of the ignition. I pulled it out last night and tested every combination of the five wires I could think of and the only change that I saw was between the red and orange wire which connect after you turn the key. All other wires seem to be unlinked in both positions.

Could it be a grounding problem. The fact that it does run for a while and then start to act up almost seems like there could be a charge accumulation in the system somewhere, but where.


Send me any ideas or suggestions... I'm coming to my wits end...

Thanks in advance.


Re: qt50 electrics

i'm going to say check the switch, or better yet by-pass it completely, see if it sparks.

hope this helps

Re: qt50 electrics

Thanks Ryan. Which wires should I short to do this... the two that connect when the key is turned?

And what are all the other wires for?

Re: qt50 electrics

A kill switch (which im guessing the "thumb switch" is) has a simple function. It grounds the ignition so no spark can be produced.

Some bikes have 2 wires leading to the kill switch. One wire comes from the (hot) ignition and one wire is a ground wire, connected to the engine block perhaps through the frame..

The switch connects these two wires together, "grounding" the ignition and killing the engine.

Other bikes have only one (hot) wire going to the kill switch. When the switch is activated, the body of the switch makes contact with the frame (and through it the engine block) so it grounds the hot wire, killing the engine.

Both systems do the same thing..they ground the ignition.

I am gonna guess that your broken switch sometimes makes contact and some time doesn't.. Maybe a wire is exposed and vibrates and touches something.. So sometimes the engine sparks and runs and sometimes it won't.

Fix the switch. Or, remove that switch and secure it's wire(s) so they don't short the ignition whenever they feel like it.

Re: qt50 electrics

Your ignition switch is another matter.. It has several wires, probably 4.

Two of the wires connect the ignition and allow the engine to run. The other 2 wires are just like the KILL switch wires and, when you turn the IGNITION switch off, the engine dies.

Fix that broken kill switch. i think it's at the root of the troubles.

Im not positive about this but it's a common way the these bikes are wired. Get a manual and a wiring diagam for your bike and study it.

Re: qt50 electrics

To make that a bit more clear:

When you turn the ignition switch ON or OFF, two wires connect and at the same time two other wires are disconnected.

The two that connect when you turn the ignition switch ON allow the engine to run. At the same moment, two wires that would normally kill the engine are now disconnected.

Re: qt50 electrics

Thanks for the info Joe. I'll check it out and keep yall updated.

Re: qt50 electrics

So I took the ignition apart last night but it turns out that's not the root of the problem. True it fails to ground the ignition circuit when it's turned off, even when I directly connected the appropriate wires, still no spark.

I ended up tracing the problem to a ground fault somewhere in the ignition circuit beneath the flywheel (presumably on the stator). Today I go and borrow a puller from NAPA again and see if I can find the fault.

Thanks for the help.

Re: qt50 electrics


Apparently conventional wisdom is right. If you have a messed up spark on this machine, replace the charge coil.

Now I just need to find a replacement.

Thanks again for the help.


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