Melex conversion question

[Lydia3pg]

Hi, everyone,
Apologies beforehand- I know there is a Melex subforum, but this is more of an electric-to-gas conversion question.
I have an early 90's Melex (I think it's a 412), and put in a 10hp Tecumseh motor, a TAV2 (Comet 30 series knock-off) TC, and one of the F-N-R go-kart gearboxes (Forward ratio is 1.13:1 or something close to that). I have # 40 chain with 10 teeth on the output sprocket and 14 teeth on the input sprocket to the final drive. From what I can find, the final drive is 12:1.
With this setup I expected the cart to be at least as fast as stock, but it is painfully slow- like, 7-8 mph. I've watched the TC and it does its thing, engine revs up nicely, but the thing just doesn't get out of its own way.
The belt isn't unusually warm after repeated test runs, so I don't think it's slipping. I've checked the response of the gearbox and it engages normally.
Any advice? Did I get something really wrong in my ratios? Is the torque converter too small? Thanks!

[slonomo]

What RPM are you running at? Top speed is determined by final drive ratio, tire size, and engine rpm. There is a calculator that will help with this.

https://www.buggiesgonewild.com/speed-calculator.php

I don't know how you can find the final drive ratio on that setup. You can try rolling the cart on the ground 1 tire revolution and count how many times the secondary clutch spins. Not sure how we can get final ratio from that.

Any mechanical engineers in the house????