sprocket size

[getting kart smart]

I built a go kart and am putting a 6.5 hp motor on it from harbor freight. I am getting an 11 tooth clutch 35 chain. It has 18 inch tires (8 inches wide) I want plenty of torque. Top speed maybe 20 mph. What size sprocket will I need to achieve this? This kart is full size and built from sch 40 so its quite heavy. Any input would be appreciated. Thanks

 

[gtmud]

I am running a 10T jack shaft sprocket with a 60T final axle sprocket. Average speed 45. This is using the Preditor 212 with a series 30 torque convertor system using a 7" driven. Works well hauling around 185 lbs on a yerf-dog 30032 cart.
Depending how heavy the kart is you might want to opt for the next size up engine.

 

[OzFab]

You're into jackshaft territory there; 9:1 ratio will give you 21mph & a bucketload of torque...