Gee wizz Matt,

Sorry to hear it's still a bear to start. There must be something different between your bench and installed setup. Any ideas? Sounds like it won't pull prime with the choke closed. Maybe you could try soldering the hole in the choke plate shut.

What is your proceedure for priming? On my updraft twin I close choke, advance the throttle to full, rock the prop twenty times or so, check to make sure the choke plate is wet, then set the throttle to high idle, turn the ignition on with the choke closed, flip once and get a pop, open the choke and two flips it's running.