Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Could the fuel supply from the tank, be restricted? Sounds like a lack of fuel, not governor or carburetor jets. Make a test line from the fuel pump inlet, the line from the tank, and drop it back into the fuel tank filler opening, to bypass the tank outlet up to the fuel pump. If no change, the fuel solenoid in the base of the carburetor may not be staying open.
The revving up and down can be from a coil not firing. It's just that you have to start somewhere. I like running a cylinder balance test, loosen the spark plug wires and with engine idling,remove one wire at a time. Engine should continue to run, if engine dies when either wire is removed, the opposite cylinder is not firing. Check it for spark and fuel. If engine is only running on one cylinder, it will cause this.
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