How do you Adjust carburetor on a 300ex ATV?

Answer 1

Most carburetors suffer from gasoline that has turned to varnish inside and water that has entered through humidity, washing, and/or condensation. A rebuild will allow you to clean the parts and clear the jets.

Adjustment usually involves a warm engine that is mechanically sound and has had the valves adjusted with a clean air filter and new plug. There are adjustments to the throttle cable that should be performed first to ensure that the cable has sufficient slack and does not bind or tense when the handlebars are turned to lock in either direction.

The carburetor has adjustments capable at the fuel screw, idle screw, float height and the throttle synchronization tang located under the plastic cover on the right side.

The needle has a circlip on the top that can be repositioned. Honda's stock position is in the middle slot or 3rd notch. Moving the circlip towards the top groove (with un-grooved needle tip pointed down) leans the mixture and conversely toward the bottom richness the mix.

The synchro tang should be gently bent to allow for 0.1-0.3 mm (0.004-0.012") of gap between the spring loaded piston throttle valve shaft arm and the tang on the throttle link. This whole assembly is the upper actuating arm under the black plastic cover and located above the throttle arm that the throttle cable mounts to.

The pilot screw located under the carb next to the float bowl in an upside down orientation should be gently seated and then backed out 2-1/4 turns for stock location.

The idle should be set at 1400 rpm +/- 100 rpm.