Suggestions.

I have a 2.5 I have been out of pocketbikes for awhile but Im going to get back in. Could someone give me a good refresher course on upgrades.

Right now I just have the cag wheel upgrade and an oneil brothers rear sprocket. How many teeth did the stock sprocket have?

also Does anyone know where I can get a pull start assembly and if any upgrades for the cable exist?

What performance parts do they make for the 2.5? And how much power can they make with the upgrades?

thats what Im trying to find out.

around 5.5hp is the limit in power. swap to a 14/14 or a 16mm carb, dig up an old Mossbarger reed block, use the newer pipe, port and polish the cases, lighten and balance the rotating assembly.
IMO cheaper and easier to just sell the 2.5 and move to a used polini 910 6.2 w/c (also a mini) or another used euro. Polini sells everything you need to build a 6.2 910 into a SP, 40 or 50cc open.

Where would be a good place to get these parts? are any after market chinese bike parts interchange able?

and how would I do this?
"port and polish the cases, lighten and balance the rotating assembly. "