QuestionYou were asked this question on 5-22-2010, but the answer was a little confusing to me. I have a 2005 Honda TRX-90 that will not keep running until it has warmed for 30 minutes or so. It has been this way since I bouught it from the showroom floor, and I see online that a lot of owners have this problem. I cannot find what might be the idle screw, if that will even help. Where is the screw? Do I have any options other than selling this ATV and passing along the problem? By the way, the showroom salesman DID tell me that the TRX-90 was cold-blooded.
AnswerRoy, looks like the idle mix screw is not capped, unless there is a limit cap on the end of the screw head...
http://www.motosport.com/atv/oem-parts/HONDA/2005/TRX90/CARBURETOR?mmy_source=oe #5
It already has a #40 idle jet, which is pretty big for most 90cc engines. If you have part throttle issues, I would get a very thin washer and shim up the needle in the slide.
I would definitely check the valve adjustments, verify the compression readings before you go too far.
These engines should be "warmed up in about 2-3 minutes" under normal conditions and tuning.
I would check for any intake manifold air leaks, including vacuum lines that are attached to other items. A bad diaphragm will cause an air leak, which makes them run lean at idle. It appears to be a vacuum line on the air suction valve system that could be an issue. If you suck on a vacuum line attached to a diaphragm and you can't hold the vacuum signal, then there is an air leak at the diaphragm.
Can't say that I have worked on one of these, but there are universal principles that apply to all 4 stroke, carbureted engines. They need compression, spark at the right time, fuel mixed at the correct ratios and an engine that is sound, mechanically.
Make sure that the spark plug cap doesn't have more than 5k ohms resistance values.
Bill Silver
