L and H Screws Adjustment Tool

Make a simple tool for adjusting 21 spline mixture screws on your 2-cycle equipment.

You will need an old Phillips screwdriver with a shank 3/16 inch in diameter and some polyethylene tubing that has an internal diameter of 11/64 inch. The tubing can be bought at most hardware stores. If you do not see it in its proper place on the display, check things on the floor. In our hardware store it is nearby on the floor, not on the rack.

Cut a piece of tubing 1 1/2 inches long.

Push almost 1 1/4 inches of the tubing onto the screwdriver.

Push a little of the tubing onto the adjustment screw. I place my index finger back the amount I want to go onto the screw. Around 3/16 of an inch is adequate. You want enough of the tubing on the screw to grab the screw, but not so much that the tubing comes off of the screwdriver when you are trying to remove your tool.

Small engines come adjusted at the factory. I have a new chainsaw. It seemed to me the engine was running rich. The engine sounded a little rough. The exhaust seemed a little blue/gray. And, the spark plug had some black soot. I used this tool to lean both the L and the H screws about 1/16 of a turn. I have not checked the spark plug again, but the engine seems to run more smoothly and have more power. The exhaust does not have as much blue/gray smoke, but appears mostly clear.

Make your adjustments after the engine has warmed up. Make changes in very small increments. It might be helpful to write what you did in case you need to restore settings to where they were before you began. For example, write, “1/8 turn CCW.”

Even though your carburetor mixtures were set at the factory, continual vibration while running means they can and do go out of adjustment. This tool is easy to make and use. It is also less costly than a tool with 21 splines.