mini motor STILL WILL NOT START?

my boys mini motor 50 cc air cooled has died it had no power when i lifted back wheel of floor it went slower and slower then stoped i managed to start it 2 days later but when i touched throttel itdied again hasnt started since i put on a new carb changed s plug changed all gaskets i checked piston all seems ok got compression when i pull the pull start .so know when i try to start it it wants to go when i pull the pull start it wants to go right at the end of the pull please any body got any ides