I was in the same boat a couple years ago when I bought my Mega Moto MB212 mini bike. I wanted a little more rpm out of the engine but retain the governor. When I got the bike the governor was set at 3620 rpm. I know these engines in stock form will take 5000 rpm and still be fine. I wanted to increase the governor speed to about 4500 rpm. I first adjusted the throttle stop screw and that got me 3800 rpm. I watched several videos and the only thing they really showed was how to bypass the governor. Then I remembered a few years ago a local go kart track had a class where they were using a stock 6.5hp Harbor Freight engine. They could run an aftermarket air filter, jets, and exhaust. Other then that it had to stock. They had a 5000 rpm maximum with the stock governor still in place. I made some calls and found one of the guys the was racing that class and he told me how to achieve a higher max governed speed. you have to move the governor spring farther out on the lever. In stock form there are 3 holes. It should be in the farthest hole from the shaft. The key to getting more rpms is to drill and hole farther out on the lever.
View attachment 122532
I found this picture on the internet of exactly where to drill the hole. The key thing is to try and keep it in line with the other 3 holes. I did this to my mini bike and now I get a governed 4800rpm. Before I found this out I tried making the spring shorter and it never made much of a difference. I also tried the zip tie through the spring to keep the spring from stretching, I found that the zip tie mod did't increase the rpm but made the governor seem to react quick and it seemed to smooth out the operation.