Motorcycle Repair: 1988 TRX125 Revving Low Idle Issue, honda bikes, vent hose

Question
Recently got a 1988 TRX 125.  Has run great for the first few rides but began stalling whenever my wife stopped.  In the field, I attempted to adjust the idle screw with no reaction.  The ATV also was over revving after touching the throttle.  The only way I could stop this was by choking.  This would return it to the idle state.  Later I adjusted the throttle cable as it did have too much play.  It does not appear to be sticking (as that is how it is acting).  Pulled the fuel petcock screen, nothing there.  Sprayed WD-40 around while at idle with no increase in RPM.  Before I remove the throttle cable and needle from the top of carb I need to know what I'm getting into.  The mixture screw has no affect on the idleing of this machine either.  The idle screw is doing a little something now but we can't go riding like this.  Help!  I have a CLYMER for 50-110 Honda bikes.  Is this going to help me any?  Thanks...Jeff
jeff.learn@sylvania.com

Answer
Hi Jeff,

I suspect either a dirty or varnished carburetor and/or a pinched or collasped vaccum or vent hose. It could be other.

I recommend thoroughly cleaning the carburetor and then try adjustments again.

Measure cylinder compression and check valve clearances. Both must be within service limits for the carb to function properly. If compression is low, perform a leak-down test.

Learn about reading the appearance of the spark plug. Visit "www.ngk.com/sparkplug411.asp" Review left hand menu topics, selct "Plug Problems" to learn more.

I'll send a few tech files to your email.

Respectfully,
Mark Shively