Dear Mr. Know-It-All,,
I have a 2008 YZ250F that I use for trail and play riding. Up until recently, the bike was good, started nicely and ran fine. Then, two weekends ago, it started right up, and a few minutes into the ride it wouldn’t run down low. It kept dying and would only work when I’d rev it to the moon and float the valves. I barely made it back to the truck. What’s the deal?
Mike, I’d bet that your machine sat for a bit before your last ride, like maybe a month? Here’s the dilemma: today’s fuel goes bad quickly, and when this unfortunate process happens within the confines of a carburetor, the residue plugs some very important canals that let fuel flow into the engine. The bottom line is that your pilot jet is clogged. I’ve taken carburetors apart and cleaned them with some success (contact cleaner and compressed air), but it’s a better plan to replace the jet with the same size that currently has been working adeptly in your powerplant. And, in the future, drain the fuel from your float bowl after every ride! I do this on every power-driven machine that I own, from my lawnmower to my weed whacker.