82, Qt50 work great for 10 minutes then dies..help please

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82, Qt50 work great for 10 minutes then dies..help please

Postby martman » Tue Jun 25, 2013 9:36 pm

Hello, I have a 1982 yamaha QT50 that as been sitting in a barn for 20 years and I want to get it running !
Here is what I have Done so far !

- Replaced piston / Cylinder / head with new gaskets (old looked good but at this point did not want to fool around).
- Before replacing piston I have filled the crankcase with WD40 to the edge of cylinder and let it sit for 2 days (just to be sure i did not have a broken / dry seal and there was no leak !
-Cleaned gas Tank and oil tank fuel valve (got gas going to carb)
-Replace fuel filter / hoses.
-Cleaned carburator / bowl etc. (dismantle)
-did pre-mix gas oil (just in case oil pump not working)
- check exhaust (external end)

- Replaced spark plug (no sure if it is the right one (BR6HS) that what it had before.
- Replaced coil
- installed Right Plug BP4HS
- Replaced the Spark Plug Cap with a NGK
- Replaced CDI box
- Checked Exhaust and exhaust port ...they are ok.
- I have replace the fuel cap and tried to run it with loose cap.

It will run for a fiew Km or 1 or 2 miles got it to go 45 km/h super nice, I tought that i had it to run finally. after doing 10 minutes of riding it boggs down and die... (like the fire is quiting).
I wait 10 seconds then restart it and work for a fiew feets then die..
even with the fuel cap off !
Check visually reed valves and looked fine.

Can it be the coils behind the magnet flywheel) ?

I am goiing crazy and I really want it to run !
do not know what to do anymore !

thanks for your help !
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re: 82, Qt50 work great for 10 minutes then dies..help pleas

Postby RebelRider.Mike » Sun Sep 22, 2013 3:19 am

Had any luck yet?

Maybe its heat related. An electrical component working while cold, but failing when hot?

Sounds like you have a really small window for troubleshooting before the problem goes a way. Can you confirm no spark? Like, maybe with a tachometer tool bungeed to your handlebars?

1979 Puch Free Spirit
1987 Honda Rebel
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Re: 82, Qt50 work great for 10 minutes then dies..help pleas

Postby Arlie1180 » Sat Jan 31, 2015 10:17 am

Charge coil. It gets warm and craps out.
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