I have family in shanghai (Zhongtan lu, west of central station) and always buy a ton of stuff when I'm there.
Are you sure its 200cc, because what they call 200cc is actually only 158cc 58,5mm It will fit without any mods and doesn't require a long stroke crank.
Real 200cc requires a long stroke crank and 63mm cylinder. I have never seen those kits on sale in shangai.
In Taiwan you can also get or 62mm 174cc. It requires engine case bore out in most 125cc engines.
Did you go to 'scooter street' JiaoJi Lu? That's a fun place to hang out.
But the mechanics are really quite incompetent as you've noticed, indeed they don't know what a jet is, I also notited it and hoped it was limited to that specific shop
.
Well at least on 4stroke most of the time the original jet is good enough. (As long as you don't increase the compression too much).
This is my shop:
http://shop33076546.taobao.com/
Be sure to ask for a discount
By the way my advice for a decent exhaust:
http://auction1.taobao.com/auction/item_detail-db2-2a19c1316e738fad9259d988e1774ad9.jhtml
The really cheap chinese exhausts (those at around 100 yuan) will sometimes make you lose power.
So your next steps are:
-realise it's really only 158cc or 174cc, and you hopefully included a matching!!!bigvalve head. This set will give you maximum 10% or 20% power increase.... Don't put a 61mm head on a 58.5mm cylinder
-Add an A8 sports camshaft (80 yuan)
-Add a bigger carb... But be carefull with the 28mm slide carbs they sell (oko/koso etc...) probably have a 2stroke setup and they don't sell mainjets obviously.