Two-stroke carburettors have a lot in common in the way they operate. Before adjusting the carburetor, check the condition of the air filter, exhaust system, pipes and clamps of the intake and exhaust systems, the appearance of the carburetor, the presence and condition of the nozzles, needles, dampers. Warm up the engine to operating temperature.
Instructions
Step 1
Adjust the fuel level in the float chamber. To do this, adjust the float height according to the instructions given. The accuracy of setting the fuel level will seriously affect further carburetor adjustments, be careful. When adjusting the operation of the carburetor with the throttle valve closed (adjusting the idle speed), take no less care, because further adjustments depend on it. This is due to the fact that the idle system works at any position of the throttle valve.
Step 2
Adjust the idle speed using the idle jet, the quality screw and the screw for the amount of fuel mixture. Look for the idle jet on the carburetor body; access to it opens when the float chamber is removed. The quality screw is usually made of brass and sits on the outside of the carburetor on the left side of the carburetor. The fuel mixture screw is located above the quality screw. With the engine running and warm, using the quality screw, set a stable idle speed by unscrewing this screw from its zero position. Adjust the idle speed using the fuel mixture screw.
Step 3
A transitional mode is considered to be a mode of operation of the carburetor in which its throttle valve is open by an amount from 0% to 25%. To ensure reliable engine operation in the transient mode, select an idle jet, adjust the idle speed and the size of the cutout in the throttle valve. It is seldom necessary to change the last parameter. In most cases, check the idle adjustment, fuel level (see point 2) and the carburetor valve shut-off needle to adjust the transient mode.
Step 4
On four-stroke motorcycles, the accelerator pump is activated in the transient mode. Most often it is driven by a separate spring. Adjust the booster pump by changing the spring rate and by changing the dimensions of the supply and bypass jets.
Step 5
Features of setting the carburetor with partial opening of the throttle valve (25-75%).
For the mode of operation with the throttle valve open by 25-50%, adjust the gap between the needle and the walls of the carburetor tunnel. To do this, change the diameter of the needle (needles differ in the diameter of the cylindrical part with a step of 0.01 mm). In the operating mode, when the throttle valve is opened, make 50-75% of the adjustment by changing the position of the carburetor needle higher or lower. You can replace the needle with a sharper or fuller one (along the profile of the conical part). To access the needle, remove the carburetor cover. On most motorcycles, the carburetor will need to be removed.
Step 6
Adjust the carburetor in full (75-100%) throttle opening mode by changing the size of the main fuel jet. It can be accessed from the outside of the carburetor when the drain plug of the float chamber is removed. Check for correct adjustment either by ear (with sufficient experience) or by the color of the spark plug insulator. To do this, take a test drive on full throttle. After 45 sec. after fully opening the throttle, turn off the engine and remove the spark plug while driving (in neutral). The insulator should be dark brown. If the insulator is black, lean the fuel mixture. If the color is orange, enrich the mixture. If the color is reddish-brown, completely replace the used gasoline, as it contains harmful metal-containing antiknock agents.
Step 7
Some motorcycles have additional jets that are used at high speeds and are controlled by a solenoid valve. Adjust the quality of the fuel mixture at high speeds by replacing these jets.
