Where does the starter motor go on the yamaha yq50 2002

Joseph, Check the attached links starter and parts for 02 yamaha. Good luck
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Yamaha DT125 Starter Motors Relays eBay
http://www.cyclepartswarehouse.com/?gclid=CMv9hPvags0CFQmSaQodpcIDqg
Starter MotorsCyclepedia
Motorcycle Starters

the starter motor has one power wire from the solenoid that is bolted to the terminal on the starter, there is no ground wire the starter is grounded from the mounting

If the starter motor spins but the motor does not turn over, the problem will be the starter clutch. You can buy many of the individual clutch parts at Babbitt's. If that doesn't work out, Google motorcycle salvage yamaha and see what you can find there. Please rate my answer. Thanks. www.babbittsonline.com/pages/parts/viewbybrand/default.aspx

The one way clutch that engages the starter motor to the flywheel is chattered or damaged and needs to be replaced. The starter motor turns a small gear that is connected to a large gear by a small chain. On the side of the big gear is a smooth machined surface that the one way clutch grabs when the starter is engaged. The surface is chattered and the three grabber rollers wont jam or grab on the surface unless it is smooth therefore the starter spins but the motor does not. You will probably have to replace the large gear and possibly the three rollers also.