When your cam pushes open the valve, it will allow for the gas to come in, or exhaust to come out. You don't want them open when you are compressing the gas before the spark plug ignites. When the spark plug ignites the fuel, it burns and pushes the piston down to make the crankshaft turn...
That is a peanut tank. I would check out low brow customs out if Ohio. Here is a link to the tank on their site. They can point you in the right direction for a cap. They're great guys!
http://www.lowbrowcustoms.com/p1626/buy/m-c-parts/gas-tanks-amp-accessories/gas-tanks/lowbrow-customs-p-nut-tank/
If you leave the gov in, it will probably keep it under 3600 rpms. I think that is about where they kick in. That's about the same as the gx200, I think. It will definitely have more torque.
I think it would be far cheaper and a lot easier to build a motor mount for a motorcycle engine. Find an older Japanese bike being sold as a project and stick the motor on your cart. I found an RD 350 for free. I'm not gonna stick it on a cart, but I bet you could easily. I bet an 80cc dirt bike...