Often the question arises “Can I make this 3.5 hp engine make my go kart run?” The answer is, as Archimedes said “If you give me a long enough lever I can move the world.” And he was right, the longer the lever, the easier it is to move an object.
The same goes for drive systems. The steeper the ratio, the easier the engine has to work, and the more likely the go kart will move. The down side is the slower the go kart will go.
That is why in cars they have what is called “Grandma gear” or “1st gear” because the car will go real slow, but be able to pull stumps out of the ground.
On a go kart the way to get the ratio steeper is to increase the driven gear on the drive system. There becomes an obstacle in that the driven gear on the rear axle can become larger than the rear wheel and then actually become a “wheel” itself digging into the ground.
The way to get around this is to break up the rear sprocket into multiple sprockets. We call that a jackshaft. Jackshaft arrangements are used frequently on go karts that are either under powered or are extra heavy.
The go kart plans sold on the GoKartGuru.com web page do not require a jackshaft for normal flat surface driving, however, if the go kart needs to climb hills frequently a jackshaft is required for hills over 10 degrees in slope.
The Go Kart Building 203 Course goes into extensive detail about how to maximize your drive train so that you can get the maximum performance out of the engine size that you have selected for your gokart. In this course charts are first used to demonstrate the overall performance curves for the weight/hp selection that you have selected.
If you want quick answers there is a program that is included with the e-book package, that gives suggestions about what you can do to change the overall performance of your go kart drive line.
Bottom line is that there is an optimum drive system that will work for your go kart, despite the small horsepower that you might have available to you. You make the sprocket large enough, or the ratio steep enough a small engine can move a large load.