The most common motorcycle carburettors have five basic adjustments. Basic adjustments are made with their help, additional adjustments are made individually, depending on the brand of a particular carburetor.
Instructions
Step 1
Locate the idle mixture quality screw on the carburetor body. Tighten this screw to enrich the fuel mixture and slightly reduce the idle speed. This screw adjusts the operation of the carburetor in the throttle opening mode to ¼. On some carburetor models, this screw must be loosened to enrich the mixture. The idle stop screw can also be found on the carburetor body. It limits the lowering of the throttle valve. Tighten the screw to raise the throttle valve and increase engine speed.
Step 2
Adjust the quality of the fuel mixture using the metering needle, which can be fastened in various positions with a spring latch. The adjustments made with this needle affect the carburetor in operation up to ¾ full stroke. Install the spring latch in the lower slot to richer the fuel mixture. To deplete, move the latch up. On some carburetor models, the latch can be adjusted to 8 different positions. In addition, the needle can be attached without a latch.
Step 3
Adjust the quality of the fuel mixture for operating the carburetor in full stroke mode by selecting the main jet with a spray. The selection of this jet will also affect the operation of the carburetor in all modes. In various carburetors, the jet can be located both horizontally and vertically. If there are several grooves on the shut-off needle of the float chamber, adjust the fuel mixture for all operating modes. To make the mixture lean, move the needle higher relative to the fuel level in the float chamber.
Step 4
On carburetors with no idle system, adjust with the metering needle, main jet and idle stop screw. On carburetors of older models and simplified carburetors, adjust by changing the size of the gap under the throttle valve using the stop fitting.
Step 5
Warm up the engine before adjusting the carburetor. Start by adjusting the idle speed. To do this, screw the stop screw on the mixing chamber cover all the way. Install the spark plug clean and secure. On a four-stroke engine, set the ignition to late. Start the engine and close the throttle valve by hand. If the engine stalls, begin to loosen the idle stop screw little by little until the engine runs steadily with the throttle closed.
Step 6
Then use the screw of the quality (composition) of the fuel mixture to set the maximum engine speed. After that, use the idle speed screw to reduce the idle speed until signs of unstable engine operation appear. Thus, adjust the carburetor by alternately increasing the RPM by leaning the mixture and decreasing the RPM by reducing the gap under the throttle valve. When stable engine idling at minimum speed is achieved, unscrew the screw for adjusting the mixture quality by ¼ turn and lock it, preventing it from shifting from the set position. Please note: if the carburetor is worn out, it will not be possible to achieve high-quality idle adjustment.
Step 7
When adjusting the carburetor at medium operating conditions, keep in mind that moving the metering needle up will increase the throttle response of the motorcycle and increase fuel consumption. If throttle response and fuel consumption are satisfactory, do not reposition the metering needle. If the spark plug is clogged with soot, lean the fuel mixture by lowering the metering needle one or two grooves. To eliminate knocking and back flashes in the carburetor, raise the needle 1-2 positions.
Step 8
If the engine does not reach full power at full speed, test the carburetor with a different main jet size. To increase engine power, install a jet with a 10-20% higher throughput.
