2t oil in the gas tank.
Get a roll of solder from the hardware store. Pull out the spark plug, and feed the solder into the cylinder till it hits the cylinder wall.
You need to spin the piston thru one fire cycle with the kick start. That will push the piston into the solder up against the head, and squish down the solder to reveal how much clearance there is between the piston, and the head.
This is actually a critical step. If the clearance is too small the bike will knock at mid-high rpm eventually breaking something. or if it is too large a gap the bike will not develop full power.
You want the gap between the top edge of the piston, and the head to be 0.5 - 0.8 mm for a Malossi sport cylinder. I have run them as high as 4mm gap. This is called the Squish band, and is critical. The way it's adjusted is by adding or removing cylinder base gaskets or shims
