Motorcycle Repair: Nighthawk throttle issues, vacuum hoses, air leaks

Question
Hi Bill,

We have a Nighthawk 250 on which the throttle doesn't spring back to the neutral position normally.  It will return, but very slowly.  Any ideas on what I should try to do to fix this?

Thanks,
Bridget

Answer
Bridget.... Please clarify if the engine idle speed isn't returning down properly or that the actual cables are preventing the throttle from closing fully.

You have to look at the cable connections on the carburetor and watch what happens when you open and close the throttle. If you close the throttle hard and you hear a nice snap/click sound, you know that the cable control system is functioning properly.

You can see some illustrations of your bike if you go to
http://www.powersportspro.com/partsfish/login.asp and register quickly. Choose HONDA, find the model  CB250 Nighthawk and the year, which you didn't provide. For the most part, the engine/carb is the same, however.

High idle issues can come from either a damaged diaphragm on top of the carburetor, air leaks due to vacuum hoses being loose or damaged from the evaporative control system (check all the small vacuum hoses going to the carburetor), evaporative control purge control valve defective, cables that are deteriorated inside, sticking from corrosion or the wires fraying inside the cable sheaths, cables not adjusted properly (need a little slack in the cable adjustement, so there is some free play at the throttle), handlebars bent from an accident that has pulled the cables out of adjustment/position so there is no slack in them, or the cables are misrouted after a service procedure, where the tank was removed for some reason.
It is a good idea to get an owner's manual that will cover some of these adjustements and/or a service manual from a m/c shop, Honda dealer, Ebay or www.helminc.com

Bill Silver