The power piston responds to vacuum. The brass no doubt has an issue with the carb body alloy. The WD / PB may need some help from a heat gun and or a 1500 watt hair dryer. A gun cleaning brush for 22 / 32 cal will clean out the bore. Brass-O will polish and clean the piston. Go easy tapping the piston with a plastic screw driver. The brass will come back, the bore may have some oxidizeing wear. Good luck
