1992 Mercruiser 3.0 problems running under load

[gucio1]

Hi guys,
I am hoping that someone could help me out with my issue. I have read similar threads but did not find anything exactly like mine.
I have started using my boat this season and initially it was lacking power when cold but running perfectly fine when warm. (as a side note , my father in-law rebuilt the carb for me over the winter using the kit from Mikes carbs, he also swapped out the float with the brass one they sell).
Now last few times I went out it runs fine as long as I go about 10 km/h when I start to accelerate it starts sputtering and bogging down (does not shut off) eventfully it will get enough speed to start planning and it runs fine as long as I stay above 30km/h or so (I believe it just has to do with it being under less load when it is going that speed). When I look at the carburetor during the time when it has an issue going I can see a steady stream of fuel going in. The compression in all cylinders is even and good. I have replaced the fuel filter (the old one did not look bad).
At first I thought it might have been bad fuel, I have ran it down added fresh and added methyl hydrate for good measure.
I hope it is something really simple that I am missing.

Fingers crossed wise people on this forum can help.

Thank you in advance.

Paul

 

[dubs283]

there are at least two fuel filters, possibly one more. one filter in the fuel pump (mechanical), one in the carburetor and possibly a fuel/water separator.

have you checked fuel pressure AND vacuum throughout the rpm range?

 

[gucio1]

there are at least two fuel filters, possibly one more. one filter in the fuel pump (mechanical), one in the carburetor and possibly a fuel/water separator.

have you checked fuel pressure AND vacuum throughout the rpm range?

I have checked the filter in the carburetor and it was clean and looked good. I am not aware of where the water separator filter would be. Same with the vacuum, I tried figuring out where the port is but can't find it. Watched some videos but still not clear.

 

[dubs283]

I have checked the filter in the carburetor and it was clean and looked good. I am not aware of where the water separator filter would be. Same with the vacuum, I tried figuring out where the port is but can't find it. Watched some videos but still not clear.

water separator would be located in line between the fuel tank and fuel pump (if equipped, most 3.0 L merc engines did not come with an oem separator). the fuel pump filter is in the pump itself, need to remove the bowl to replace it.

i was referring to fuel system vacuum, not engine vacuum. need to have a vacuum tester rigged in line between the pump and fuel tank to measure, no more than 2 in/hg

 

[Rick Stephens]

Not to pick on anyone's work, but carb rebuilds are the most common thing to need doing again. To me, this surely sounds like yours is misbehaving.

 

[gucio1]

water separator would be located in line between the fuel tank and fuel pump (if equipped, most 3.0 L merc engines did not come with an oem separator). the fuel pump filter is in the pump itself, need to remove the bowl to replace it.

i was referring to fuel system vacuum, not engine vacuum. need to have a vacuum tester rigged in line between the pump and fuel tank to measure, no more than 2 in/hg

I did replace the fuel pump filter and I do not have an in-line water separator.

 

[gucio1]

Not to pick on anyone's work, but carb rebuilds are the most common thing to need doing again. To me, this surely sounds like yours is misbehaving.

I knew I should have done it myself but I was trying to be nice
I know the parts were good quality, do you have any input of which part of the carburetor got worse as I kept using the boat? Just wondering if I need to take the entire thing apart.
Thanks to everyone for their help thus far.

 

[Rick Stephens]

I knew I should have done it myself but I was trying to be nice
I know the parts were good quality, do you have any input of which part of the carburetor got worse as I kept using the boat? Just wondering if I need to take the entire thing apart.
Thanks to everyone for their help thus far.

Full tear down. Is not hard and once on the bench, no purpose in doing it halfway. That's how it ends up needing doig again the first time.