Fuel Water separator

[gobuck]

I had a new Merc 383 installed this summer That never reached the recommended max RPM. I put new props on that were 2 inches less in pitch but had the same performance. I was thinking that maybe they put the old fuel filter on that only allowed 25 gph because that was the fuel flow at max throttle. I plan on changing the fuel water separator but wondered if I should go to a 60 gph filter?

 

[Scott06]

25 is the rates WOT fuel consumption so it looks like it’s pulling the correct amount of fuel. What rpm were you getting ? and what did the installer say about the issue ? Did you verify the tach is accurate ?

 

[tank1949]

I hade Wellcraft, whose tack was 500 rps off. What was wot RPMs before new motor? Does trim in OD and/or tabs work CORRECTLY??? All rings seated by now? What is compression test on cylinders show??? Does ignition have knock sensor and it works????? What is MC ignition ###? Thunderbolt 4 or 5? Are you sure spark is advancing(simple test with timing light) . Is it timed correctly? I'd bet it is in base time and all wires are not attached correctly. My 2 cents??? If my old brain remembers the test correctly, a typical 350 marine Chevy motor that is timed and propped correctly will burn about 10 gals of fuel at 3000 rpms. A stoker will give more power and suck more gas. Check you timing for proper advance!

 

[Bondo]

Ayuh,..... The stock fuel filter is capable of feedin' up to 400 horsepower,.....

Look somewhere else,....

 

[gobuck]

Thank you for the responses. I am just pulling straws right now because the boat is dry docked and winterized.

 

[QBhoy]

What was in it before ? And is the new 383 a carb or mpi (6.2) ?

 

[gobuck]

it had a 1200 hour 260 hp merc 350 vortec. The new motor is a FWC 383 MPI
RPMs were 4100 on the old motor with 22 pitch props, and 4700 on the new motor with 20 pitch props I sent the old props to get reworked to 19 pitch. I know I need to get the RPMs to 5200 so that is what I am working on now. I thought when I got the new motor I would be able to turn the 22 pitch props to the recommended. RPMs. The new motor is suppose to have 350 hp.

 

[Scott06]

Your wot rpm range is 4800-5200 so your not far off.

What boat oat and what props - are all these different pitch’s the same prop model? I’m surprised a prop shop would say yeh could move a prop 3” in pitch I would suspect they may not actually be 19”

4700-5200 would need at least 2” lower pitch maybe 3” if you had 4700 with a 20 would think you need 18” or 17 to hit 5200 eapeciallly if it’s a big 4 blade like a revolution 4 that has a lot of bite

 

[NHGuy]

You are probably on the right track. I tried going to a bigger pitch (21 Mirage plus) when I put a home built carb 383 in where a 350 mag had been with a 19" Michigan wheel stainless Apollo. The hole shot is fine and the boat runs along well with the 21 but it only makes 4900. When I let it spin with a 19 pitch Mirage plus I see over 5300 rpm.
I think the 19 is going to stay on there. My drive is an Alpha and a 383 is more than an Alpha is supposed to handle. The 19 won't load the gears so much on takeoffs.

 

[QBhoy]

I’d think you would naturally need an inch or 2 up in pitch from a 260 5.7 carb...going to a 6.2 mpi of around 320hp. Not sure what’s going on here really. As far as I know the 6.2 mpi should ecu limit itself at around 5150 rpm though. The old carb 5.7 260 should be done at around 4800/4900 rpm