you may be onto something charger with the bowl gaskets or check valves as i notice the throttle has to travel about 1/4" to squirt fuel out either squirter. i adjusted the pump levers to .020" and still does the same thing.
my pv now is a 6.5 and my vacuum in gear is between 5-6". so maybe a 4.5 would be better?
what i don't understand is how tightening up the cam/valve lash could cause these issues.