I have a 1999 Kawasaki Bayou 300, it will not run when the choke is off. Air filter is Clean. whats wrong?

Check the breather valve on the gas cap. This is meant to be turned off to avoid spillage when transporting the atv but must be turned on in order for it to run. If it is turned on, make sure it is not blocked by dirt or something else. You can easily check if this is the problem: if it runs properly when the gas cap is removed it means that the valve is indeed blocked.

Another problem with this model atv is the carburator diaphragm that tears with age. This will also cause poor running and is easily and cheaply fixed, though it does require dismantling the carb. A good opportunity to give the carb a good cleaning.

Kawasaki 300 Bayou

The carburetor needs to be cleaned.

The pilot jet is clogged.

The pilot jet is for the idle circuit.

The choke is adding more fuel, which compensates for the lack of fuel, not being delivered by the pilot jet.

The pilot jet's opening is as thin as a pin - very easy to get clogged with bad gas.

sounds like for some reason it is not getting eneough fuel