Re: Correct Carb/intake for 5.7 Mercruiser?
You don't want extra fuel filters in the system. In your case, you do want lots of fuel water separator cartridges. Remove that extra filter when you run the boat again. The separator and the screen on the carb will do the job, keep checking them til you trust the gas.
In fact if the fuel is that dirty you will find it worthwhile to clean the fuel by repeatedly filtering it til it's clear of water and crud. That will probably take a separate pump and some gas containers but it really needs to be done before you can be sure the motor is getting the right fuel supply. If you can get to the tank sender remove it and see if the tank is clear too.
That boat should not need folks to go to the bow on liftoffs unless it is over propped, or as you suspect it might be not running right. If the previous owner put on a tall prop for more speed it could be limiting your hole shot if you are carrying more weight than he was. Can you get a look at the prop for it's pitch?
Or maybe as you are thinking, the motor isn't absolutely right yet. I don't know if that carb is a problem on that manifold. I tried to search the carb but I couldn't confirm what application it's for. I did find rebuild kits in the listings. The intake manifold is a high performance part.
What RPM does the motor get to? You should see 4700 to 4800 if it's a flat tappet motor. I think the rollers are expected to turn 5100.
Does it fall down when you go from 3/4 throttle to wide open?
You don't need premium fuel unless the motor is high compression. Regular gas stores more energy than premium. High compression motors need premium to stop detonation. So don't use it unless you are supposed to.
