Yamaha QT50 Has problem !

[BarnEagle]

Working on my friends QT50 1985 vintage. When I switch the key from start to run, the engine goes full speed. I switch the key back to start and will idle all day. Any clues to what is happening? This machine has 1500 miles on it and looks brand new. I suspect the carb is shot, but there might be something else to check. All adjustments have been made according to manual. Help!

[maddog]

make sure the half moon side of throttle slide faces the air filter...

[xrongor]

thats exactly what the start position is supposed to do. limit the rpm's. when you put it in run it removes the limiter. This is not a function of the carb.

all adjustments to the carb need to be made with the key in the run position. my guess is you have the idle screw turned in too far or the cable is frozen/broken.

randy