bn125 rpm stays up when throttle closed
 

I have been asked to look into a problem with 6 2001 bn125s. The RPM stays up to about 3000 rpm when the throttle is shut down. Owners say they were that way new. Carbs were reworked then. The bikes are used in a motorcycle safety class. They have 7 to 8 k on them at 12mph. I was wondering if this is a inherant problem or where to look before exploritory surgery. Any advice on settings or modifications to the stock setup would be smiled upon.

Welcome to KF.

All 6 bikes have this issue, the carbs are all adjusted, the idle speeds are set to 1,300 rpm? You have verified all visuals as cracks and no air gaps in the holders, the cable adjustments are correct and not binding or the rpms are not varying as you turn the bars? Looks like the mikuni BS 28 has a "coasting enrichener" I am not familiar with this carb and it would be nice to know what that enrichener is for, especially since all 6 bikes did the same thing when new. My understanding is that it is for eliminating deceleration exhaust popping but that it can be plugged which may also eliminate your problem as well. Found this pic/explaination while learning. lol Good luck on your research. Let us know what you find as well. Don't forget that the air suction valve and evaporative emission controls are due for inspection and cleaning at 6k miles.

http://www.mychinamoto.com/forums/sh...ng-Jets/page2&