Also pay particular attention as to where the hook end of the Governor mechanism spring is attached (you can see it with the close to run cover lifted as it sits to the right of the arm going into the Fan Shroud area to the adjusting mechanism worm gear/star adjuster. The hook end should be positioned below the star adjustment nut (Droop Adjustment Ratchet item 16) as I recall (it sits about 3 threads down below the star adjuster (spring is sitting level) on my MEP-002a's. I recall a member a few years ago saying their spring was dislocated in the wrong place above the star nut adjuster causing governor issues.
In addition, verify that all the governor linkages on the rod ends that the stop solenoid actuates are not broken, cracked or bent. There have been issues with the plastic ball joint & the keeper breaking as well as the rod that goes through the sheet metal hole binding up by scraping/binding against the metal hole it passes through. Not sure it would necessarily cause surging but while you are in there best to verify all the linkages are properly fastened & intact via a thorough check out.
