its when the piston moves up in the cylinder,,,it compresses the air fuel mixture whren it is compressed its ignited it cause a dhamaka ,, tht dhamaka pushes the piston back down,, and rotates the crank,, which then rotates the gears and then wheel,, so dhamaka jitna zoordar hoga utni bike kharak dikaya gi,, yani pick,, or more power will be delivered at any instant,, but there should be a limit on the compression,,
normal two strokes are not that better in creating a high compression as are their four strokes,,
2t CR (comp ratio ) is normally 6-8 :1) that means it compresses 6-8 times the original mixture,,
regarding piston,,
a piston is used to hold the compressed mixture in a closed chamber ,, then there is a question how much should the piston be in dia in comparison to the cylinder dia to hold the compression without leting it escape from sides of piston,,we want an ideal seal where no mixture passes down the piston,,so we use rings ,, after many studies it has been determined that a normal commuter/cruiser long life bike needs 2 rings for compression and 1 ring for oil ,, so agar pahla ring sa thori si compression loose ho jaya,,then second ring will do the job,,even then some small amount of compression loses 2nd ring,, so y not a 3rd ring? because if 3rd ring is installed there will be a lot of friction on cylinder walls and will quickly wear the cylinder and rings,,and will over heat engine,,
so regarding installing 3rd ring if ur mechanic knows it surely has reasonable effect on power and negligible effect on life then think of it otherwise stay away,,
regarding plug coil,,
u need a specific voltage to jump the plug end gap to cause a spark,,normal coils create any where between 10000 to 20000 volts and the plug needs somewhere 10000-15000 volts to jump the gap,, so i don't see any reason for upgrading it,,