What is your ratio and engagment rpm

I am trying to figure out what strength springs to purchase and what overall ratio would do best for my project so I figured I would as the community what they use and run from there.

my engagement rpm is whatever i want (belt slip clutch)

Forgive my ignorance, but what is a "belt slip clutch"? What does it do exactly? How does the bike act like?

the idler pully tightens and loosens the belt when the belt is loose it slips
on the small engine pulley

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Thank you. That makes sense.

Your ratio depends mostly on the hp and rpm of your engine and the size of your drive wheel. A large diameter wheel needs more reduction than a small one. From there you can choose an engine shaft sprocket or clutch and drive wheel sprocket (or pulleys) that will give you an appropriate ratio. Japanese or Chinese clones of small utility engines (7000 RPM) almost always need a jackshaft or gearbox to obtain the large amount of reduction needed even with small diameter wheels. Larger Briggs & Stratton type engines and clones (3500 RPM) can usually get a proper ratio with a clutch on the engine and a sprocket on the rear wheel without a jackshaft or gearbox.
Your weight is a factor, especially if you will be riding in hilly territory. So you see we need more information to answer your ratio question. It could conceivably range from 4:1 to 20:1 . After you provide the needed info we can help you narrow the choices and direct you to the ratio calculators available here.
This info will help us advise you about engagement RPM as well.