Hello Group,

In a previous Tech Tip, #3, we talked about cleaning and rebuilding your Keihin carburetor on your Honda CH250.

The enrichment circuit on the carburetor is controlled by the pilot screw which is located in the rear of the carburetor.

The pilot screw meters the correct amount of gasoline directly into the intake of the motor from the carburetor.

The pilot screw has a limiter cap on it to prevent miss-adjustment.

With the limiter cap in place, you can rotate it by hand in a three-quarter turn manner until it hits the stop on the bottom carburetor bowl.

Usually, the pilot screw needs no adjustment other than that from the factory unless your carburetor was rebuilt or tampered with.

Sometimes the limiter cap falls off and the vibration of the motor unscrews the pilot screw until it falls out.

Several schematics and the Honda manual show a gasket and O-ring along with a tension spring with the pilot screw but I have never found those in any carburetor missing the limiter cap.

To prevent the loss or miss-adjustment of the pilot screw without a limiter cap, go to your local hardware store and obtain a 5/64 ID x 13/64 OD O-ring and place it on the pilot screw needle, then install the tension spring then install the pilot screw in the carburetor.

The O-ring will do two things.

Prevent gas from dripping pass the pilot screw and prevent the pilot screw from backing itself out of the carburetor.

The pilot screw adjustment is done with a warmed running engine by setting the idle of the motor to 1500 rpm.

Using a pilot screw adjustment screwdriver, which is available from J. C. Whitney & Co., back out the pilot screw from its initial light seat two turns out setting while reducing the idle.

When the combination of backing out of the pilot screw and reducing the idle gives you the best and smoothest idle approaching specs, the adjustment is set.

Randy Pozzi (Rev. 02/2003)