RE: Removing varnish on 4 strokes??
get about 2 qts of castor oil and that castor oil not castrol oil. Alsoo get an old casorole dish. partialy tear down the engine. remove exuast carb backplate and valve cover and plug.
set oven to 350 degrees and bake for about 1.5 hours. get out the tooth brush and scrub it lighly. then bake another 3 hours. should be like new