Small Engine Problems? Ask an Engine Mechanic for Answers ASAP
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Remove the muffler and check the exhaust port for carbon build up. clean it thoroughly and make sure the muffler is clean also including the spark arrestor screen at the output of the muffler
This may be a compression problem but I doubt it. An easy check is to remove the carb and look at the piston. It should be clean and shiny with no makings or scratches on it. Also on the carb itself you need to inspect the welch plugs, they are sealed with an almost transparent sealer. When this deteriorates the welch plugs tend to leak and mix the high and low speed circuits when they are not supposed to.
One more thing, when the carb is apart and you can see the tab that pushes on the spring to open the inlet needle, you can bend that tab ever so slightly in order to allow more fuel to get into the carb.