I'm planning to buy a TRX90 for my son from a good friend who allowed me to take the bike home and make sure it was the right size. It's a 98 model with probably less than 20 hours and looks brand new without a scratch. After spending 3 days trying to start it another friend of mine helped me remove the head because he suspected a bent valve. Sure enough the intake was bent and there was lots of crud built up from gas that would sit in the chamber when the bike was stored for long periods. Apparently this crud caused the valve to stick and when I tried to start it the valve bent. It looks like this might be a common problem due to the design where the carburator is high above the horizontal cylinder causing the intake chamber to 'hold' gas when the bike is in storage. After I buy this bike I'll probably be running the bike empty after shutting off the fuel after a ride to prevent this from happening again. I was wondering, has anyone else seen anything like this on the TRX90 or any other bike with a similar engine configuration?
Max

 

Its a common problem across any gravity feed fuel systems regardless of type or manu. The needle seat for the float can be worn or get a piece of crud lodged in it and fuel will overflow. If you're lucky it will just overflow out the carb, but that never seems to be the case, the fuel trickles into the cylinder. I've seen bent valves, bent rods, broken kick starters, etc, from the cylinder filling with gas and then being kicked over and the motor "hydraulics". The gasoline is compressed tight faster than it can escape and bad stuff happens.

It's always a good practice to shut off the fuel. I am in the habit of doing it even if my ride is going to sit for a couple of hours. Conversely it's just as important to remember to turn it back on, as in some super zoot applications if you suck the float bowl dry WFO then you can lean it out enough to seize it.

 

I agree w/Backcountry. I wouldn't let this problem stop me from buying it tho, I consider the TRX-90 a bullet proof engine. Happy trails [img]i/expressions/face-icon-small-smile.gif[/img]

 

I thought it might be common although I hadn't thought of it as possibly being a hydraulic problem before so I guess that's something else to consider. I am about 99.9% certain that I'll buy the bike since the head will be pretty much as good as new when I'm done cleaning it up prior to reinstalling the valve. Hopefully I'll get my parts and gaskets in within a couple of days so I can start. My boy can't wait to try it out, I wish I had been so lucky when I was his age. Thanks for the replys.
Max