Mercruiser 454(7,4) dies after a while

I have a 454 (94') that always starts fine the first time of the day, after driving for 1 or 2(or more) hours the problems can come. Sometimes it works fine after waiting for 30min or so, somtime it needs more. If I try to start it at once, it wont, but if I wait 10min, it just stops realy fast, I can run i little longer time on high rpm, but it shuts down on low rpm. Its like the engine gets raw or something!

I think it has something to do with the fuel delivery system. I've changed the fuelpump, and the same thing i happening. New fuel filter. Dont think its the carb.
I'm not an mechanic, so any help is much appreciated

I assume you have a Rochester Quadrajet Carb. A common problem with them is the "well plugs" leaking fuel into the intake manifold when hot. This will "flood" the engine making it hard to start when sitting for a after you shut it down. The well plugs are on the bottom of the carb and can be sealed with an epoxy like JB Weld. There are YouTube videos showing how it's done.