Look at this chart to see the roller width difference of the #40 chain, it's 1/16" wider than the #41 and #420. Therefore, any of the 3 sizes sprockets can be used on #40 chains. However, #40 sprockets can only be used on #40 chains. Chain for Go Kart, Mini Bike | GoKarts USA®
That should do the trick, after some riding ifya find yourself wanting a bit more torque,
or it cannot reach top RPM's with your weigh/terrain, you can replace the torque converter sprocket with a 9 tooth
or even 8 for a bit more performance.
Made an exhaust from old bicycle handlebars from a thrift shop for $2. Made an air filter for the venturi since the cone filter would've hit my foot. Got my sprocket drilled, just need the center milled out now. Almost ready to rip!