Hard starting

[Scooby]

I have a 4.3 mercruiser. This motor will cold start in my driveway with little problem. Then when I get to the boat ramp it will not start without holding the throttle wide open and cranking the motor for a extended amount of time. I have the same problem after the boat sits for a few hours. I have had it to a shop twice and they say everything is ok. I just rebuilt the carb myself to make sure it was done right. Has anyone else had this problem?

 

[bondo]

Ayuh,.... Which carb,..??

The 4bbl. carbs are known to leak off into the intake, causin' a flooded start situation if only turned off for a few minutes or hours,...
Then a hard start in the mornin', 'cause the carb is outa gas,...