Hey all, I've been working on a 1998 Xpress 300. Overhauled the engine with a new piston and bored cylinder. Replaced the crankshaft due to some problems with it. New seals installed.
Hard to start. Carburetor has been thoroughly cleaned and gone through. Tried to raise the venturi slide and needle to richen up the mixture, and the pilot air screw - have tried it every 1/4 turn from about 1 turn out to 4 1/2 turns out.
With a shot of starting fluid, it will start right up, and runs great. Without that, forget it. It won't start.
If I can't figure this out, tis time for the bone-yard for this one...

 

Starting fluid is a lot lighter then gas and will try to crank when nothing else will. I'd recheck the compression and see what you have,plus normal position on the slide needle is the 3rd position from the top. Air fuel screw normally between 1 1/2 to 2 turns. Plus simple things such as making sure the throttle etc contacts in the housing aren't touching. Usually about 1/8" slack at the thumb throttle,maybe a little less on the older ones. Plus one other thing you can do is to disconnect the reverse limiter black wire(if you haven't done so already) as these limiters fail quite often and can retard spark. Item #28. Dirt Cheap Yamaha, Honda, Arctic Cat & Polaris OEM Parts & Accessories – Cycle Parts Warehouse