On Wed, 08 Jul 1998 08:10:54 -0700 Andrew Siminoff
 writes:
>Sounds like an air leak!  Check the color of the plug.  If it is 
>white--don't ride the bike.  Perform a leak down test by plugging the
intake 
>and exhaust port and pressuring the motor. 
>A simple leak can get very expensive if you keep riding.  Check the 
>boot for leaks around the carb.  Another area to check is the reed valves.  
>If they don't close all the way, then replace them (or flip them over--as 
>a temporary fix)
>Good luck,
>Andrew

The air leak observation is correct.  There is some evidence for this:
the idle goes up with higher heat in the motor.  The cases and other
parts expand, opening up some very small leaks.  My experience has shown,
especially given the better design and components of the newer bikes, the
cause of the problem is usually much more simple, in carburetion, for
example.  I even had gas cap vents do the same when they were not venting
properly.

If you do have an air leak, a good way to check is to use acetalene from
a welding torch on very low.  Do not light the torch, but instead put the
tip against suspected air leak spots while the bike is running lean and
idling high.  If you manage to get in the region of the leak, the idle
will drop as fuel, instead of air, enters the leak.  If the main seal at
the magneto is leaking, for example, you can just crack the cover and
stick the tip of the torch in.  Same for the crank case.  Take care as
acetylene is flamable of course.


Chris (CJ) Johnson
Director of Engineering,
College Park Industries, Inc.     http://www.college-park.com
(810) 294-7950 (at CPI), (616) 664-4173 (home office)
papazit "at" juno.com