I posted a while back about my merc 4.3 1991 engine being hard to start when warm. It always starts right up when cold, but after sitting for an hour it takes forever to start. This seems to be happening to a lot of you with this particular engine, and it is always blamed on vapor lock.
I found a fix, at the help of the board members here, so i figured i'd share. I too, was determined it was vapor lock. Did all the things you guys have done to fix it... run the blower the entire time on the water, let it idle for a while before shut down, open engine compartment etc. NOTHING. Still took 15-20 seconds to start after it heated up.
I found out through here it could be flooding after sitting, due to the wrong type of needle/seat being used, or something along those lines. I was told the next time i let it sit after it is warm, to hold the throttle at WOT when starting. Apparently it helps a flooded engine start. Sure enough, fired in about 2 seconds instead of 15 seconds. I also then pulled the flame arrestor and there was a little bit of gas running down the throat.
I will probably just have the carb rebuilt at the end of the season, but it's good to know the problem is an easy fix.
So before you go spending money on extra blowers, fuel coolers, check valves etc, check for engine flooding. Happy boating!