kohler sv600-0009 engine surges when the throttle is at half position and below, at full throttle no problem. when choke pulled out at 1/4 inch no problem, new carb and air filter. is it an air leak or governor
Not likely governor. More likely new carb not acting correctly. But being a Courage single don't overlook the gasket behind the black plastic carb isolator plate. That gasket can slip in some cases or tear causing an air leak.
Most likely it has an air leak between the cylinder head and the carburetor insulator block. These were not a well thought out design. The insulator block could warp and allow the gasket to suck in stray air especially at idle.
Not a governor issue, so never mess with the governor.