yz 125 running weird

[Ben1992250]

I have a 2003 yz 125 and i just started to noticed that when i take off and go threw all the gears floored, that when i pulling in the clutch and come to a complete stop my bike is idling really high like im holding the throttle a quarter of the way open. But when i take back off in first and go a foot and stop again my bike goes back to idling fine. I also put a new piston and rings in my bike recently and it did not change anything. I adjusted the air screw alot but it didn't change the high revving at an idle after riding my bike floored. What could the problem be?

 

[sharky243]

Sounds like an air leak to me. Possibly crank seals or a broken gasket somewhere. Do a vacuum test on the crankcase, this will find the leak.

 

[Ben1992250]

How can I do a vacuum test on my bike? Or do i need to take it to a shop that already has the tools to do it.

 

[sharky243]

Remove the pipe, and block the exhaust port. Remove the carb., and block the intake. Make an adaptor tool from a broken sparkplug so that you can connect a peice of hose to the top end of the spark plug shell. Take an automotive type vacuum hand pump and connect it to the hose. Apply 5-10 inches of vacuum to the crankcase and watch the gauge on the vacuum pump. If the gauge goes back to zero, you have a leak. If it holds the vacuum, the crankcase is air tight and good.