How to Jet a Yamaha Warrior 350by Kelvin Hayes
The stock main jet on a Yamaha Warrior 350 is a 145. The 145 main jet, like the main jets on all carburetors, is designed to work optimally at sea level, around 70 degrees Fahrenheit. But changes in engine performance, altitude or ambient temperature may require you to re-jet the Yamaha Warrior 350's Mikuni carburetor. The Mikuni is a small displacement, single-bowl motorcycle carb with a single main jet that is accessed by removing the fuel bowl.
Loosen the hose clamps on the air box and intake side of the carburetor with a screwdriver. With the clamps loose, you'll be able to rotate the carburetor toward the right side of the quad, allowing you to access the fuel bowl at the bottom of the carb without removing the carb.
Unscrew the four fuel bowl screws and pull the bowl away from the carburetor. Preserve the fuel bowl gasket. With this bowl removed, the main jet will be exposed. Unscrew that jet with a screwdriver. It's likely that you'll be increasing the jet size to account for higher engine performance so note the size of the main jet.
Insert a larger sized jet for greater engine performance and colder temperatures or use a smaller size jet for warmer temps and higher altitudes. Re-jetting will require engine testing. Once you've reinstalled the fuel bowl and tightened the fuel bowl screws, push the carb body back into a level position and tighten the hose clamps on the air box and intake sides of the carb. Start the quad and allow it to idle. Test the throttle and ensure that the acceleration characteristics are crisp and responsive.
Repeat the re-jetting process, if poor idle or acceleration characteristics persist, until the correct jet size is achieved.
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