So many questions!
Before we begin, what is the actual displacement of your pushrod motor? Are you limited by displacement in your racing class?
This is the carb I like for 200 / 230 China motors:
http://www.ebay.com/itm/Carburetor-C...4979d6&vxp=mtr I jet them with a 112 main and 27 slow at sea level for a 200, 115 / 30 for a 230.
This is the intake tube I have on my atv:
http://www.ebay.com/itm/30MM-MANIFOL...fb51b8&vxp=mtr Not sure if it costs any power, but I doubt it. The air and fuel are happily sucked uphill by engine vacuum.
The clutch isn't normally that difficult; certainly no more than an average CG125. If you can't find a mechanical problem, perhaps this would help:
http://www.ebay.ca/itm/Chrome-Hydrau...4c0632&vxp=mtr
You're using a 17 tooth countershaft sprocket and a 24 tooth rear sprocket? I can't believe that little motor can use such tall gearing. I figured that 40 teeth would be the outer limit for a rear sprocket.
I would certainly try a racing CDI, or even a programmable unit.
I've never messed with timing. I would focus on smoothing the intake port and polishing the exhaust port first.