1990 regal valanti won’t start

[crhodes18]

Bought my first boat recently and replaced exhaust manifolds instantly, ran great for 5 minutes then shut off without bogging down or anything and hasn’t started since. I’ve since replaced the fuel pump and put all new gas as well as spark plugs, I’m completely stumped and have no clue what to do now. I’m against taking it to a shop since I want to be Able to use it this summer, any help is greatly appreciated