I've seen a few posts about speed governors recently, so I thought I'd share this info.
There are four main ways in which speed governors work on simple engines:
1) Restrictor in the exhaust. Either a 'washer' in the exhaust port, or by design of the muffler/pipe itself. This is (in most cases) easy to defeat. Either remove the washer, or replace/modify the limited exhaust pipe/muffler.
2) Restriction of carb opening. This is done with a screw or other stop in the carb body, and sometimes with the throttle control / twistgrip itself. Again, relatively easy to defeat.. remove whatever is preventing full opening of the throttle.
3) Active flyweight or vane governor. You see this most often on lawnmower/snowblower motors. As RPM increases, a vane (driven by air from the flywheel) or a set of flyweights (driven by RPM of the governor) push-back against the throttle. A tip-off to this style of governor, is that the throttle doesn't directly open the carb - it acts on a spring which tends to open the carb, but can be overridden by the force of the governor.
4) Late timing. Sometimes engines are detuned by simply retarding the spark timing. Find a suitable earlier timing, and run with it.
Hope some of you found this helpful. Please feel free to correct/modify/add info as needed.