I've a problem with a GX120 in that I start it and it just revs up to maximum rpm and stays that way. The throttle butterfly is linked to the governor arm via the usual arrangement (weak spring plus rigid control rod) and the whole assembly moves freely. The governor arm is also linked to the throttle lever/plate assembly via a spring that is only just mildly tensioned when the throttle butterfly is closed. In its resting state there's a good amount of play in that spring and it's not the case that the spring is too short and continuously pulling the throttle open. The throttle lever isn't jammed open; the whole assembly is new and the return spring works to close the throttle lever position back to normal/idle position
While the engine is running, if I grab the governor arm and move it myself then the engine behaves normally. I can push it all the way to the kill switch end of the engine and rev the engine down to a slightly too fast idle, I can move it to the other side and rev the engine up but what I can't work out is supposed to shut the throttle down/move the governor arm towards idle.
If I let it go then the assembly moves to about 85% WOT and stays there, revving the engine high.
If this engine behaved normally, what would make the governor arm move towards tick-over position? I'm trying to work out if there is something faulty with the governor inside the crankcase - it seems to move freely enough on the outside; if I remove the arm I can twiddle the governor shaft through about 90 degrees with a hard stop at each end with fingers - no idea if any of this is normal