The correct carburetor settings are crucial for the optimal operation of an engine and even more crucial when trying to maximize performance. To help you get the most out of your engine, we'll explain the role of the various carburetor components.

The first thing to adjust after installing a carburetor is the main jet. It is best to start with a slightly too large nozzle (rich mixture) to avoid the risk of piston seizure.

Run the engine at full throttle for several hundred meters and then immediately turn off the ignition. Remove the spark plug and read it, which means check the the colour of the electrode. If it is black, the mixture is too rich, i.e. the main jet is too big. If it is white, the mixture is too lean, i.e. the main jet is too small, and there is a risk of overheating. If the spark plug electrode is light brown, it means that the mixture is perfect, i.e. the main jet has the right size. The main jet is adjusted by decreasing the size in increments of 5.

This is followed by adjusting the mid-range rpm using the carburetor needle. Pull the throttle about halfway and listen carefully to the noises of your engine. If the engine misfires and sounds like a 4-stroke, it means the mid-range mixture is too rich. The needle clip should be raised one notch, which will cause the needle to go down one notch, making the mixture leaner at mid-range rpm.

If the engine is choking (running out of gas), the mixture is too lean at mid-range RPMs, so the needle should be raised one notch, i.e., the clip is lowered one notch.

As soon as the engine sounds constant in mid rpm range and there are no misfirings, you can adjust the air mixture screw.

It plays a relatively brief role when you open the throttle, after that it has no influence, i.e. only during off-the-line acceleration. When you go full throttle, the RPM should rise directly. If this is not the case, you need to adjust the air screw. Opening the screw means the mixture becomes leaner, closing it means the mixture becomes richer at this stage. The adjustment should be made in ¼ turn increments.

Once the engine runs smoothly at all speeds and no longer misfires when accelerating, the carburetor is optimally adjusted.

Another component that is rarely adjusted since the original jet usually fits, is the pilot jet; it acts like the main jet, except that it only affects low RPMs, but after that it is not that important.

CARBURETOR TUNING DIAGRAM