piston type difference?

ya in your case, i would just pick up a compression tester(the screw in type) and see what you get. Anything in the 120-130 range is excellent and anything above 100 is easily runable. If she is under 100 then i would look into doin some work in the next 6 months depending on how much you ride.

In case your wondering, to do this test all you need is the compression tester. You unscrew your spark plug, screw in the tester, hold the throttle open and kick until the needle stops climbing. The highest it goes after say 20-30 kicks is usually your compression, but i like to do this test about 3 times to get a little more accurate reading.
 
I have a compression tester that one of my dads friends gave me when I was doin work on a go kart a couple of months ago, its not screw in you have to have someone hold it tight to the hole the plug goes into for it to get any kind of seal, I might do that before I get all the brakes installed, basically whenever my friend stops by to help me again.