Gotta send this thing home. The best design is having the clutch on the jackshaft like every motorcycle ever built. CGs and whizzers are set up like that. I don’t know why so many of us with industrial engines (including me) put it on the crankshaft. It may be a trend carried over from minibike or go-kart experience. In the case of the sportsman flyer it has to do with packaging to have the pedal spindle doubling as the jackshaft, which both final chains sharing endpoints.
A clutch on JS accomplishes several things. For one it keeps the bike skinny. Second, the clutch spins slower and doesn’t heat up or wear out as fast. Third, a stock clutch for a slow go kart can be used. To get a good top speed we have to gear higher, and have to mod the clutch to engage higher at the torque max of the engine. Putting it after a primary reduction allows one to run a stock clutch with a lower engagement reducing heat, cost, and effort during replacement.
Then there is the primary drive type. A lot of vehicles without an enclosed primary reduction use a belt, because chains and gears will overheat without lube. Ie- Whizzer (vbelt), huasheng 50cc, the new Surron Ebike (flat toothed belt). Primary chain and clutch heat was a MAJOR problem for me on my 212.
Whizzers also use a vbelt final. I believe this only works with low-torque motors, or higher torque motors under perfect conditions. Problem is the small front pulley with not enough wrap-around. This design allows one to use a standard bicycle rear wheel with brake and freewheel sprocket built in.
Here’s a couple examples of good designs in my opinion:
msrfan: belt primary, clutch on JS, with final chain drive to not slip under the big motor torque of an 8hp Briggs (300cc?)
Surron ebike drivetrain: high reduction keeps an electric motor revving higher and running most efficiently. Also the jackshaft is concentric with the swingarm pivot so there is no change in chain tension throughout rear travel.
people riding off-road with highly modded surrons tend to snap the belt landing jumps; a chain primary kit is available.
My next build will have a v-belt primary and chain final. I have not yet decided on the clutch but I will start with a typical $30 max torque clutch and go from there. My first setup had a tensioned v-belt clutch which worked well but was incorrectly set up, and the final drive was a disaster before I learned how to do it right and I scrapped the entire drivetrain (I tried using a 16” rim for a sheave, it didn’t work). I plan to figure it out for real next year.