Small Engine Troubleshooting Problems? Ask a Mechanic Now.
Is the choke on the carburetor opening? Is the inlet screen on the water hose clean? Choke has to e open, or engine will run rich, and will not develop full power. A look at the spark plug, being black in color , will show if engine is running rich. The inlet screen plugged with debris will keep the water from getting to the pup in quantity, to keep the pressure going.
What you say , is that it runs fine without a load. Try draining the fuel bowl on carburetor , to see if it may have water in it, and is getting too little fuel.