I agree with JimH
my calculations for 3000-3600 rpm on the engine is about 11-16 mph. You are geared down 2.2 to 1 from your clutch sprocket to your 10 tooth jackshaft sprocket. You are geared down 6 to 1 from that 10 tooth jackshaft sprocket to your 60 tooth wheel gear. Your 16 inch wheel has a circumference of pi x D (the 16 inch diameter), which is about 50 inches. So your bike moves 50 inches every time the back wheel rotates one full revolution. Your clutch sprocket needs to turn about 13.2 times (6 x 2.2) to turn your wheel once, and have move you the 50 inches.
So overall that is a pretty good bit of reduction. So your speed is low, but your torque (power) is high.
You can get rpms for your engine off the Tulsa Engine Warehouse website under the link for engine line drawings.