You're right Mike, your engine is running too lean - the plug colour should be brown. Is this the engine with the petrol tank below the carburettor? There is a mixture adjustment screw alongside the primer button if I remember correctly, and with the engine running fast, turn this screw out until the engine falters or blows black smoke - and then turn it back in again until the engine starts to run smoothly. Its also a good idea to replace the diaphragm between the carb and the tank if it has been disturbed.
John
April 2009
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