I recently purchased a vintage go cart for $75.00.I have since replaced tires,hubs,rims,sprocket,and chain. It has a 5hp Briggs&Stratton engine. It idles great. The problem is when i push the gas pedal down it starts cutting out. If i play around with the gas pedal i can get it to stabilize enough to take off. If it gets up enough speed i can mash on the gas,then it will run wide open.That is until you slow down or stop. Any ideas as to what could be the problem?