69 55hp runs poor after cruise

[King of the Sea]

I have a 69 55hp that starts and runs fine, gets on plane great and will run WOT all day, UNTIL i let off and try to get back on it, sometimes it will die or start to backfire a little bit, but usualy it will run smooth as a top, just not rev up enough to move, if i shut it off, it will not start again (ive been towed back the launch twice by some nice gentlemen) I have a new fuel pump diaphram and coils, fresh plugs, am i dealing with a carb issue or maybe points? (the time/temp issue is throwing me for a loop) any help or adivice is much appreciated