TKM BT82 » Walbro Carb
The carburettor should always err on the side of richness for maximum performance and engine life. Settings are different between the junior and senior engine because of the use of the restrictor plate on the junior engine. Recommended starting settings are: Junior Low Jet 1.9 turns out High Jet 0.4 - Junior Intermediate Low Jet 1.85 turns out High Jet 0.4 - Senior Extreme Low Jet 1.85 turns out High Jet 0.4 - For engines fitted with clutches you may have to reduce your advised Low jet setting by up to 0.3 turns and increase your High jet setting by the same 0.3 turns to get your engine to tick over correctly when engine is hot.
These are safe starting points which will give a slightly rich (safe) mixture. If the engine is too rich, then by using small amounts turn in the High jet until the carburation is correct. This will probably be between 0.4 and 0.25 of a turn out. You can check the mixture by removing the cylinder head and inspecting the piston crown. Dry black is perfect. Dark to light grey is too lean and could lead to engine damage. Very wet and oily is too rich and will cause lack of power and possible fouling of the spark plug.
It is very important to keep your entire fuel system meticulously clean. If carb problems do occur they are often as a result of minute particles of dirt upsetting its fine tolerances. Your petrol cans should be kept clean inside and swilled out occasionally. Filter your fuel through a funnel into the tank and make sure that the funnel is clean - keep it in a plastic bag when not in use. You should use a filter either inside the tank or instead/also an in-line filter in the pipe. Replace the in-line filter from time to time. Make sure the inside of the tank is clean.
The carb must be spotless. If you have a problem strip and clean it through thoroughly, ideally using an airline, and finally put a little WD40 spray on the needle valve tip. It is very important that the 'pop-off'' setting for the needle valve is correct. When tested with a carb pressure tester the needle should release at 10-12 psi and hold steady at no lower than 5psi. Adjust by carefully bending lever arm.