What year-model is your engine? If 10 or more years old, have you changed the fuel filter if it has one? Also, if it does, replace it and cut the old one open. If full of black specks change your engine fuel lines and fuel pump diaphragm (kit). If tan chips of crud, your engine to fuel tank line and bulb. I have had both these problems with my engines and these problems are easily overlooked......On my current 2002 engine, I bought last year, I don't know how many times I stared at the engine, looking right at the white fuel filter on a black engine (thing was glaring right at me) and after a lot of wasted time and money, chasing "butterflies", it was my problem on not getting WOT operation. Cutting it open it was full of tan crud from the tank to engine fuel line. On another 2002 engine I had, after 10 years on ethanol, the fuel line degraded and small black particles of fuel line clogged the filter and carbs.