What rear cassette gears w/ shift kit?

I run a Tanaka 47R engine with shift kit and 8-speed cassette. The rear gears are 11t-34t; these work well enough for me. No custom cassette needed, and I normally skip every other gear. I shift from 1st to third to fifth to seventh. I'll use second gear when accelerating from a rolling stop.My first gear is 37.09:1. This gear is excellent for climbing steep parking structure ramps, or when gridlocked on steep hills. If I could have even steeper gears, I'd use them.

Your 80cc engine has built-in gear reduction...4.1:1, I believe.

Engine sprocket is 10 tooth; with a 17t jackshaft sprocket, that's 1.7:1.
Multiply that with 4.1 to get 6.97:1.

Using a 9t jackshaft gear and a 44t chainring sprocket, that ratio is 4.888;1.
Multiply that to 6.97 equals 34.069:1.

Using a 30t chainring sprocket and a 34t first gear, you get 1.1333:1. Multiply that to 34.069 equals 38.61:1.

First gear will be excellent for climbing very steep hills and ramps. It is akin to using a Happy Time single rear sprocket of 94 teeth.

Sixth gear relates to a 47t sprocket.

Seventh gear is like a 36t sprocket.

Eighth gear likens to a 30-tooth rear sprocket.

Even though you might have flat roads with no hills, stiff gearing will also help traverse steep driveways.

My friend Hawaii Ed uses a similar 80cc combination. He also uses the HD freewheel and added welded gusset for bracing the shift kit bracket.