One thing I have had success with. I bought a one gallon can of carb cleaner at Advance Auto. It has a small basket in the can to hold the parts, which is very convenient. I take the front and back cover off the carb and remove the two rubber parts, then i just drop the rest into the cleaner and let it soak for 15-30 minutes. this stuff will remove all the varnish and gummed up oil if there is any. Take the thing out and reassemble and you are good to go.