Are you sure the pee hole is not connected to the thermostats? Some models of Merc Require the thermostats to open to pee. Also on muffs should take far less than 90 seconds to bleed out the air.
The way that Choke works is you pushing the key and it closes the little port. When you release the key it uncovers the port. Your primer mech would have had the square know. The newer style has a round knob.
