I get most all my kits from gabike.net
The Racing kit with billet high compression head runs well, just don't try to put an Iridium plug in it.
The new 2015 EPA certified Grube Skyhawk 66's are coming pretty soon but I the Starfire kits are OK, they come from the Yang Dong engine factory as well, and were the predecessors of the Skyhawks.
I just ordered a couple hard to find 48cc Starfires yesterday for a couple of new customers that can't afford to run afoul of the law at any cost.
Darn near $200 a pop delivered but in the YD factory tradition sport 2.5L tanks with the new good petcock with reserve, new CDI style with no white Aux wire, and nicer back sprocket.
As far as the mods go, I would recommend the expansion chamber for the exhaust pipe.
It helps the engine breath better and provides a noticeable increase in performance.
That is not entirely accurate.
An expansion chamber exhaust is sort of like a reverse turbo charger.
It captures all the unburnt fresh fuel that goes out the exhaust when the engine is trying to do exhaust and intake at the same time.
They don't make your engine rev faster for more power like other options, it runs in the same RPM band as stock, but each explosion is bigger due to the extra concentration of fuel.
In short, a properly tuned X-chamber will make a 48cc almost as powerful as a stock 66cc power wise.
