Hi, If the bike has a lack of compression this should show by the exhaust dribbling oil & hard to start. Check crank seals. If all is ok in this region check ignition timing (1.8mm BTDC ). Check points gap( 0.3 - 0.4 mm ). Check spark plug (NGK B6HS Gap 0.5 - 0.6mm ). Next check Carb. (Clean fuel no blocked jets , Air screw 1 1/2 turns out , 86 Main jet , 049 needle clip position 2 ,Pilot jet 34, Float level 23mm + or - 1mm.
Also check the clutch isn't slipping. Good Luck !