yamaha qt50 By swm0625 (Read 831 times)

[swm0625]

have a QT50 that a friend got for free. He put a jug and piston and new carb on it but it had no spark. That is how I got involved. i rebuilt the magneto and installed an NOS cdi. Did some other wiring cleanups and it start fine.
Now for the interesting - rear wheel while I'm kicking rotates in the proper direction. Once running the tire orbits in reverse.
When the tires are on the ground and you give it some throttle it will drive in reverse.

He swears he didn't get into the trans. It does rotate clockwise per the arrow on the flywheel and it is a rear kick.

Before I dig into the trans . . . anyone have any thoughts? Bashan , JR , Alleyoop ,

[czmdiver]

Sir you have a very rare occasion and very cool situation were the Two Stroke Fires but then goes in Reverse Direction, you do Not have a Trans problem.
Anyone who has worked with old school two stroke either Tether or Radio controlled airplanes has had the Two Stroke Start then go backwards, the old COX two strokes were famous for this. we just threw a rag in the prop to stop her then restart.
Knowing this is for real I have only had one full size Two Smoker do this a Kawasaki 550 jet ski, King Factory Kawi wrench tried to tell me this is impossible until I put the Jet Ski in the water and started it, the Jet Ski went backwards in the water.
The Flywheel key was sheered near a perfect 180 degrees out so she would fire and run in reverse but run like crap.
You may have a bad CDI pickup and she is firing any time she wants, there should be a Ohm ressitance spec you can find and test. I had Yamaha DT400 CDI pickup go south and she fired any ol time she wanted to.
Or again confirm you do not have a sheered or partially sheered flywheel key.
Good Luck

[swm0625]

key is good. So it is a timing issue. I believe there are slots on the contact plate for the magneto. Would advancing or retarding have any effect?

[czmdiver]

Jul 17, 2018 20:51:29 GMT -6 swm0625 said:

key is good. So it is a timing issue. I believe there are slots on the contact plate for the magneto. Would advancing or retarding have any effect?

No you will not be able to make enough of a adjustment.
I would suspect the CDI pickup, on my old Yam there was a Ohm resistance number and can be easily tested, mine had like no resistance so I can only spec;ate it fired anytime it wanted to,It kicked back so bad I broke the Kickstarter shaft in half.
  God luck

[swm0625]

ok - call me a skeptic. The spark is fantastic so I am having trouble getting my head around the CDI being the issue.
Contact plate on this bike is non adjustable. But I am also not sure if the flywheel is original to the bike either is I gently removed the center lobe section and rotated it one set of hole CW. Marked the original location with a punch and temporarily riveted it on to try.
2 kicks and it was spinning in the correct direction. You were right it was timing. Appreciate the reply and the info. You got me to look someplace I was sure was ok. But it's correct now so I can put it back together and give it back. Thank God

[czmdiver]

Jul 18, 2018 18:25:49 GMT -6 swm0625 said:

ok - call me a skeptic. The spark is fantastic so I am having trouble getting my head around the CDI being the issue.
Contact plate on this bike is non adjustable. But I am also not sure if the flywheel is original to the bike either is I gently removed the center lobe section and rotated it one set of hole CW. Marked the original location with a punch and temporarily riveted it on to try.
2 kicks and it was spinning in the correct direction. You were right it was timing. Appreciate the reply and the info. You got me to look someplace I was sure was ok. But it's correct now so I can put it back together and give it back. Thank God

Thank you very much for the reply and update.
You found out you can make a Two Stroke run backwards, its kinda cool really..
You kept a open mind and listened to someone with immense two stroke experience..
This is valuable information for someone with this issue in the future.
                   Good work,,, Cheers.