Though it's not as easy as machining the head, my personal preference is to machine the base of the cylinder. This will lower your port timings, but will keep the positive squish angle of your cylinder head in check.
For the purpose of street use, you will notice power increase enough to justify bolting it on as-is without the machine work.
What is your goal with this scooter? That is one thing that's important when deciding your direction in tuning. Deciding what you actually want in the end can save a lot of headache.
If you liked your bike before, but just want some extra power, install the kit and go with it. If you want to squeeze every last drop out, measure the port timings precisely, make note of them, machine the base of the cylinder (which will lower the port timings) then if you so choose you can raise the ports back up to where they were, but with an Airsal that may not be a good choice (mine had 144 degrees transfer duration!). Better to concentrate on the angles of the transfers. Doing this type of porting is going to require a few special tools from
http://www.ccspecialtytool.com/ or similar if you don't already have them. I apologize if this is already information that you know. You will spend several times more money on the tools, machine work, etc. than you did on the cylinder to begin with. Such is the curse of in-depth 2-stroke tuning.
The head is cheaper and requires little fixturing to hold in a lathe - just a mandrel. The cylinder requires an expanding mandrel that's quite a bit larger. It's easier to machine the head, for sure - you just have to make sure you keep that compression ratio in check. Several people caution that running higher than 12:1 on pump gas will cause detonation. I have run higher on some engines with 93 octane, but generally speaking I think you should keep it at or lower than 12:1.
This is a video I made on how I set up a degree wheel:
After you find true top dead center, you can align the piston to TDC with a thin coating of grease around the rings. Then you can fill the cylinder through the spark plug hole with liquid poured from a graduated burette. You can fill to the bottom of the plug hole and call that the "combustion chamber volume" or you can be even more precise, and fill to the top of the plug hole and subtract the spark plug's displacement. For general purposes that aren't "on the edge" (which most Airsal cylinders are not) filling to the bottom of the thread should suffice for assuring you the combustion chamber volume's value.
After you get the combustion chamber's volume figured, you can get compression ratio by adding combustion chamber volume (CCV) to cylinder volume (CV) and then dividing the result by the combustion chamber volume. So CCV+CV / CCV. If I measure the CCV at 5cc's and the engine displaces 50cc I add the two together and get 55cc, then divide by the CCV (5cc) to get 11:1 compression ratio.
Instead of doing all of this, I think you should switch your exhaust from the Next-R to the Tecnigas RSII. You will notice a good performance increase.
Doing all of the above is fine and great (seriously) but without a good pipe to support the cylinder, it's not quite pointless, but close enough to it. I am no longer a fan of Tecnigas exhausts myself. The quality is just not what they used to be. I use mostly Leo Vince for street use. They do not rev as high as the Tecnigas, but they are by far better build quality. One of these days, I will dyno the difference between them and share the results.
Do make sure to either fix up your cylinder bolts (sounds like you may have done that already?) or install the Minarelli cylinder studs so that you don't go through a bunch of head gaskets.
I would post more, but it's after midnight, and I'm quite exhausted. It's been a long day.
Forgive me if I don't check in to Kymcoforum as often as I used to. I'm tied up a lot with my own site, work, family life, etc.
~Josh
