Hi I'm New to the forum. I have a problem with my carb. It will rev up on its own. the only way to bring the rpms down is to choke it but this only works for so long when that stops working I shut it off and start it back up. because of this I can't shift up or if I am in mid shift this happens it won't catch. I have cleaned this carb many times.
What is the problem and a possible solution. Any help will be apprciated.

 

What you are saying is rpm hanging, right? Sounds like an air intake leak problem. As you may know, your 300 is known for having a very leaky intake design (dirt intrusion into the jug as well). While engine is idling, spray some aerosol type carb cleaner on the air intake path to pin-point the exact leaking location (rpm would increase for a second or two).

 

It was an electrical problem. When I pressed the starter button it would shot a spark and when i let go it shot a spark which caused a backfire. I cleaned all wires and starter button and had no problem since.