[tabora]

Surging is not usually a throttle issue. Start by draining the carburetor bowl and letting some fresh fuel flow through it. Surging usually indicates a lean condition and water/contaminants in the bowl will also cause that to occur. If that simple step doesn't cure it, try cracking open the fuel cap and see if the surging stops. The vent may be partially clogged and fuel isn't flowing properly until the engine throttles up. If the problem still exists, it's probably time for a proper carb cleaning including the jets.

 

[tabora]

I suppose it's possible that the idle screw is just set too low. What RPM range is it surging in? What is the actual full Simpson model number? Is it the MSV3024-I or something else?