Timming is what the camshaft is in a full scale car. It is the "moment" that the crankshaft intake valve opens and closes in relation to piston position and the "moment" that sleeve ports open and close in relation to crankshaft position. It can make your engine pretty damn fast, it can make it worth crap too.

You can probably do that 0.15~0.25mm cut in your tg's crank with only gains, the tg is fairly tame to start.
Yes you can get the bigger carb but here's rule of thumb, more than 5.5 is for bashing, more than 6 is for drag racing.