Governor/Carburetor problem (I think)

Symptoms: Tractor wouldn't start and run when it was suddenly needed so the wife bought me a new Zenith from the local dealer rather than wait for a rebuild kit for the M-S this last winter. Starts and runs great. Didn't pull well under load so I rebuilt the governor in February thinking that might be the cause. Again pulled and checked the governor last night to verify freedom of movement and measurements (pretty certain that it's all spot on), installed and took a short test drive with no improvement. Grading, mowing, hills (any significant loading) all result in the engine slowing with no noticeable effort on the part of the governor/carburetor to maintain the rpm.

Am I perhaps fighting a carburetion problem even as well as it starts and runs? Ideas on where else to look for improvement?

I'm not a mechanic by any means but my son and I are willing to jump in and try most anything. Any and all suggestions appreciated.

Thanks, Rick

In most other carbs, cars, mowers etc. I have seen there is a little spring thingey that attaches the needle to the float that pulls the needle away. It seems that the Zenith relies on gravity and pressure only. IMHO, it's not the best design.

-- Hope this helps.