Tri Rider In Need of Low End Power

perhaps try switching out that tranny for a cvt, if you can find one that will fit? I dont know if the huasheng engine will accept a cvt or not. its worth a try though.

Is that a 3.25:1 gearbox? If so, you have a 7.8:1 overall ratio right now! Assuming those are 24" wheels, the trike would go ~18MPH at idle!

You definitely need some more reduction in there. If you switched to #35 chain and sprockets, you can run up to 10>44T, tho you'd lose the freewheeling.
That will give you 14.3:1, or 10MPH @ idle. Like you said, not much of an improvement, since you'd be going 30MPH @ 6000.
That's the same as top gear on my own build, and I can't really take off in that gear!
Using your existing gearing, you can also do this by switching to 16" rear wheels

If you were using a 4:1 or 5:1 gearbox, you'd get closer to the optimum reduction for your setup, which I estimate about 18:1 overall.
With a 4:1 gearbox, you'd need 45T on that axle; with a 5:1 36T. Closest to your existing gears is 7:1 and 26T.

There are no suitable CVTs for these motors being sold, unfortunately.

I have a worksman trike that I want to motorize. I live in calif. so I can only use the 4 stroke engine that has no low end torque so I was thinking of using an electric hub motor for the front wheel. With a little pedaling I could probably get it going fast enough for the piston power to take over and relieve the electric. The front electric would help it get up hills too. If the electric was only used to help start it and get it up hills it would probably last a good while between recharges. If you take this approach I would be very interested in the results.