-Guidelines for correct jetting
(fuel mixture adjustment)
In order to check your bike fuel air mixture & thus running performance, take out the spark plug and check the electrode; the color should
be golden brown. If it is white, the engine is running too lean (not enough fuel). If it is black (sooty color) it is too rich (too much fuel). If it
is white & black, the engine is VERY lean & causing misfire, which you should be able to detect whilst riding. As your jets are close to
what they should be for local area, minor alternations can be made by adjusting the needle correct on your carb, maybe change for
different size jets.
To add more fuel, raise the needle one notch. This is achieved by removing the carb from the engine, removing the throttle slide,
removing the needle & adjusting the position of the circlip.
Conversely, if you need to reduce the amount of fuel, drop the needle one notch. Re-assemble the carb & continue testing, remembering
to check the color of your spark plug. Once you have achieved the correct full load fueling, you can get the idle mixture screw. The 140 –
160 engines like to run very rich at idle, this way you get a clean progression from idle jet to main jet. To achieve a richer mixture, turn the
air screw (next to filter) clockwise. Ideal speed may need to be adjust at same time to keep engine running.
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