We got a new engine!
We tested out the gokart with the small Briggs and Stratton lawn mower engine but it only had enough power to push the gokart with nobody in it. Therefore, we decided that if this was going to move it was going to need a bigger engine. A quick trip to Harbor Freight solved that problem. We were able to get a 6.5 hp horizontal shaft engine for $100. It is one of those honda clone engines so it runs very well, just like a Honda.
Link to Harbor Freight Honda Clone Engine: http://www.harborfreight.com/65-hp-212cc-ohv-horizontal-shaft-gas-engine-epa-69730.html