Any ideas? It's a 25HP 724CC Commercial engine on a Kubota zero turn mower. I've read that small engines have a spring in parallel with the governor linkage that looks like it doesn't do anything, and when that breaks the engine hunts. There's no spring on this one, but there's also no slack in the linkage to take up and on one end of the linkage I don't see any place to attach a spring. (on the other end, there is a hole the right size with nothing going to it)
Doesn't matter where we set the throttle, it does this until we engage the blades. Then it runs just fine. Any problems I can think of in the fuel delivery system would fail under load instead of when unloaded.
I've mentioned this mower here before. It does have a fuel problem that I've kinda figured out is grass clippings or leaf debris in the gas tank. When it won't run, we disconnect the fuel line at the filter and blow it out back towards the tank with an air compressor, then it's good for a few months again.