Although the Merc service bulletin does not specifically mention it, I would check for drips from the discharge tubes in the venturis after the engine is shut off. Run it as you normally would, shut down and then remove the flame arrestor. Look down the carb throat with a bright LED flashlight and see if you see fuel pooling on top of the throttle plates. Also make sure the throttle plates are compeltely closed when the throttle is pulled all the way back in neutral. If not you might have to adjust the throttle cable.
The only vehicle I ever had that did that was our old 1970 Ford Torino with a 302 V8 and a 2bbl Autolite carb. It had a bad auto choke before we got it, which never opened. I fixed that but the engine had heavy carbon build up due to running rich all the time and it did diesel after shutting it down. I cured it by running GM top engine cleaner through it a few times, literally chunks of carbon came out the exhaust! After that it was much better.
