The most common cause of engine surging (rev up and down) is a dirty air filter.
The engine will over-rev depending on what size engine you have
Most commonly caused by bad belts. It may go away as you rev the engine.
Its an electronic sensor
The Engine might rev a Little higher , which might make the go-cart go a Little faster - or blow the Engine up.
When you step on the gas and reach a certain speed the transmission should automatically shift out of first gear and go into second gear. First gear causes the engine to rev higher but gives more torque at the wheels to help the car get going faster. Second gear allows the engine to not rev as high and makes the wheels spin faster but with less torque. The higher the gear the less torque you get at the wheels but the engine does not rev as high. Even though the transmission is not shifting into a high enough gear do not guess that the transmission is the problem because many times the engine is not putting out enough power for the transmission to shift properly. The only way to tell is to put it in neutral and floor it. If the RPMs do not go nearly to the max on the tachometer have the car tuned up fully and see if you still have problems. I hope this helps.
Nothing causes it it happens on its own
When u want to go to downshift bring Ur rpm down to 1100 but in out of gear and rev the engine rpm to 1400 or 1500 don't over rev it.
Do not go over 40mph or your engine will rev to high and be damaged
It's probably your IAC.
Thanks for your interest. Yes, when you rev car engine while driving keep your foot on the brake the time of revving it up, but remove it before dropping the shifter into gear if you want to slide around as you leave the area. Put it in neutral rev and back in gear, go as fast as you want. Here always need a practical performance. So be careful.
Check the engine for proper cylinder compression. If the pressure is low then a blown head gasket could be leaking and causing the problem.