First I'd check to see if the drive clutch has lubrication on the inner angle of the cover on the drive clutch. Check with GTC to see what sort of lubrication they offer and what specific suggestions they as the company who is offering these clutches which they claim perform to the same quality or in their test even better. Is your engine 3/4" or 1"? If its 1" the clutch claims ability to operate at 13hp very easily though Comet never claimed it could operate past 8hp in any boxes I saw.
If the heat is entirely in the drive clutch this may be an issue of overloading on cheap springs, I havn't even seen one of their clutches to judge in any manner. A larger assembly assuming this is 1" may be able to handle what you attempting much better than this one, but possibly it would do the exact same thing and you'd have just spent another 300+ dollars to hear the sad story that you just can't work with this.
My final point is that changing engagement does not change the gear ratio, karts like this were never designed for the speed you are attempting to reach, switch the drive sprocket back to 54 and see what it does.... it it stops overheating then you know you have an absolute answer. Can you give me a solid reason you desire to attain this speed in a kart which was not designed for anything over 35? The steering is all stamped, the wheels are not balanced, all the tires are NHS, this just seems scary to me. If you do in the long run desire to attain these speeds in a kart build a buggy from scratch using a powerplant similar to this, the money does not need to go to waste, you can use the same axle but many changes need to be made for safety.
