Have you seen 5000+ rpms at any time with your tach? Just wondering if it is the govenor holding you back or if you have hit the power limit of your engine. Personally I like a governor so I don't have to watch a tachometer while screaming across rough terrain. With this in mind, I'd see if you could adjust yours for a couple hundred more RPM. This is easiest to do if you unbolt the gas tank and just shift it to the side a bit, careful not to disconnect the gas line. Under the gas tank, you will see a spring connected to the governor arm. You will also see a thinner spring, don't mess with that one. There is usually a series of holes in the governor arm. Take the spring out of the hole it is in and put it in the next hole that will tighten it. Then put it back together and give it a try, repeat as necesary.
Are you still running the stock airbox and exhaust? If so, you might be reaching the power limit of the engine. Install a high flow intake/ exhaust, rejet the carb accordingly and see what that does for you.
All that said, 36 mph on an off road minibike is plenty fast for me. Stopping distances with just a rear brake start getting mighty long at that point. I've got a mikuni sitting in a box just because I have no desire to go any faster. Call me old if you want, but I like my parts the way they are!