Just an update for anyone interested in my float vent valve saga.
When I went to fit the replacement vent valve lever for the one which was missing off my front carburetor, it became obvious that the small brass pin assembly on which it acts was seized. Checking the rear carburetor confirmed that the pin there was seized as well despite the fact that this did already have the correct vent valve lever.
Copious squirts of PB Blaster and use of air over a period of a few days did nothing. A quick check with Joe Curto confirmed the need to take more drastic action. Seeing if getting to the inside end of the brass pin assembly by pulling the drilling/airway plug would help.
Nice easy on-the car job. Punch, drill and tap the plug 5/16” UNC. Pull plug. Easy access to the other end of the brass pin assembly. Squirt of PB Blaster and a light push on the pin end and voila! Freed pin. A little more working and everything was just fine.
I did polish the exposed end of the brass pin using a small wire brush on the end of a Dremel before fitting the vent valve lever back.
I used helicopter tape to seal the drilling/airway as a temporary measure so that I could a quick road test check. With the car up to temperature, I did an initial set-up the vent valve. Everything seems fine.
I’ll source and fit some replacement plugs this week and do a final set-up for the vent valve.