How do I Adjust a Carb on a Honda 300EX ATV?by Robert Good
The Honda FourTrax 300EX is a small all-terrain vehicle (ATV) that has a lot to offer. This ATV is a cross between a sport quad and a sportsman. The 300cc four-stroke engine produces a lot of power and torque. Only newer FourTrax 300EX models have fuel injectors; earlier model have carburetors. Adjusting a FourTrax 300EX carburetor is not difficult, but you will need the adjustment chart in the owner's manual.
Locate the carburetor on the top middle of the engine. Turn the gas valve to the off position. Locate all of the small gold-colored pins on the surface of the carburetor and the small metal screw on the lower bottom right side of the carburetor.
Turn the air valve screw clockwise until the head of the screw touches the frame of the carburetor. Turn the air valve counterclockwise three full turns. This sets the air valve screw halfway out, a position that should allow you to ride at almost any altitude and almost any riding condition.
Locate the jet chart inside the owner's manual and read it. This chart will list the tension specifications, and the positions and placements of the jet pins. You will need to adjust the jets the same way you adjusted the air valve screw.
Items you will need
- Owner's manual
- "Haynes Honda TRX300EX & TRX400EX and TRX405R/ER ATVs Owners Workshop Manual: 1993 thru 2006 282cc, 397cc, 449cc"; Mike Stubblefield and Ken Freund; 2007
- "1993 Honda TRX300 Owners Manual TRX 300EX Fourtrax"; Honda; 1993
- Zedcor Wholly Owned/PhotoObjects.net/Getty Images