Jake - First thing to do is make sure the carburetor is properly adjusted. If the idle mixture screw is set too lean and the power screw too rich the engine can surge under light load conditions. But assuming the carb is set OK here's some things to check: 1 - Loosen (don't remove) the two clamp screws at each end that fasten the tube running between the governor riser and the carburetor. Wiggle the tube around to make sure it's free, then retighten all 4 screws. 2 - If that doesn't help, remove the slanted cover from the top of the governor riser to expose there the bell crank inside. With the governor handle set at "idle", try moving the bell crank up and down - it should move freely. If it does not, check for a binding in the crank pin or bellcrank bushing. 3 - If it still surges, disconnect/remove the carburetor from the manifold. Check for free movement of the throttle shaft - it should rotate freely without a hint of binding. If it does not, time for a carburetor rebuild. 4 - If after all the above the engine still surges, the problem's inside the governor itself - a binding output rock shaft, sticking thrust bearing, worn flyweight pins, etc.
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