Someone else had the same problem only a week ago...here's the same thing I told him:
The air valve is part #1203W...the little square plug on the front of the pump. It has has a check valve inside that opens on the downstroke of the piston to allow a little air to come into the (unused) top half of the pump cylinder to stop the "vacuum kick." If this check valve doesn't open to allow air into the top half of the pump cylinder, the handle becomes very difficult to pump in the dry mode and wants to jump back and smack you in the face. This ONLY happens in the "dry" mode. The problem, that little check valve is stuck.
The cure: Straighten a paper clip and poke the wire into the hole in that little plug to push it loose...it's spring-loaded and you should feel it move in and out when he presses the wire in there. If that doesn't fix it, remove the square plug (it threads into the pump) and clean it. Wrap some teflon tape around the threads to seal it when you put it back. If THAT doesn't fix it, replace the air valve.
It's a $30 part that's NOT in the rebuild kit, but the good news is, the average lifespan of an air valve is at least 10 years, which is at least half the lifespan of a PHII if you just keep it well lubricated , replace the joker valve annually, and put a rebuild kit in it about every 5-6 years.
--Peggie
"If you can't explain it to a six year old, you don't completely understand it yourself." --Albert Einstein