You ask we answer. Here's the latest in our "Ask a Mechanic" series.
Q: I have a 2013 Yamaha YZ250 that has never had problems, always maintained, but last time out the idle was way high. How do I adjust the idle?
A: The idle on your dirt bike, or any dirt bike for that matter, can be adjusted by turning the idle screw in our out depending on your needs. The idle screw is found by the choke and the location various by make and model. So check your owner's manual to find it if you don't know where it is.
However, generally you don't need to adjust the idle. Once it's set it should be good to go. A high idling engine on a dirt bike usually indicates a fuel or air pressure problem. When the engine idle suddenly runs high that usually means you've sprung an air leak, have a dirty air filter or you're running bad gas. Cross the dirty air filter and bad gas off your checklist and if the idle remains high then you might want to conduct a compression test to rule out an air leak. A compression test sounds harder than it actually is but you will need a compression tester. Read "How To Do a Compression Test On a Dirt Bike Or ATV" to get started if you need to go that route.
One last thing, did the high idle start while riding in a higher elevation than normal? Higher elevation changes the fuel to air ratio so in this instance, yes, you would want to adjust the idle screw to fix your high idle problems. Also, on a 2-stroke a high idle could also be the sign of a cracked, chipped or worn out reed
