Mercruiser 4.3 Alpha One problem - loses power

[minj]

Good day,
trying to figure out a problem I have with my boat.
Just put it out in the water, drove for 2-3 minutes to the dock.
Took the people out for a ride then after around 5 minutes it start to lose RPM, was going from 30 to 25 back to 30 then 25. The speed of the boat was probably at half. New gaz in boat and its at 3/4.
We head back to the dock and it did that for the ride back. I have to put it to idle and then give gas again, then after a couple of seconds it starts again. It seems like its not receiving enough gas. I had a similar issue with an outboard merc 50 or 60HP and I changed the fuel pump and it fixed it but in this case, the previous owner did a full tune up 2 years ago, new carb, fuel pump and more.

Apparently there are 2 filters I could check, one at the driver seat and another one at the carburator and where they are located

I cannot find any pictures online for those filters.

Any other ideas and help is very appreciated.
Thank you!

 

[Chris1956]

You might check the antisiphon valve in the fuel pickup tube and the fuel tank vent. Om my SeaRay, the fuel pickup tube had a filter (not just a screen), which became partially clogged. It limited the RPM of the engine, until I cleaned it.

 

[minj]

Thank you very much, Ill try to figure out where this is located!

 

[alldodge]

Apparently there are 2 filters I could check, one at the driver seat and another one at the carburator and where they are located

I cannot find any pictures online for those filters.

Give us a motor serial number and we can figure it out

Might be you just need to clean the carb

 

[minj]

Give us a motor serial number and we can figure it out

Might be you just need to clean the carb

Could it be OC970153?

 

[minj]

I am not where the boat is at the moment but these are some pictures I had.

 

[alldodge]

Could it be OC970153?

Yes, maybe it's coming up as a 1988 - 1992
Can have a 2BBL or 4BBL carb
2BBL Merc carb filter item 29
https://www.mercruiserparts.com/bam/subassembly/31478/951/110

4BBL Rochester carb filter item 8
https://www.mercruiserparts.com/bam/subassembly/31478/951/130

Combo Fuel pump and filter is on the block
https://www.mercruiserparts.com/bam/subassembly/31478/951/90

 

[minj]

Yes, maybe it's coming up as a 1988 - 1992
Can have a 2BBL or 4BBL carb
2BBL Merc carb filter item 29
https://www.mercruiserparts.com/bam/subassembly/31478/951/110

4BBL Rochester carb filter item 8
https://www.mercruiserparts.com/bam/subassembly/31478/951/130

Combo Fuel pump and filter is on the block
https://www.mercruiserparts.com/bam/subassembly/31478/951/90

Thanks so much - Boat is 1989 if that can help!

 

[ROY WILLIAMS]

I was the venting gas tank .... cleaned it of that screen .... my engine is running the RPM 1500 ... then my engine is over the low power ...
back in the old years I was venting the every spring ....cleaned it , using a small brass bush ..
also I was in the spring inspected it of the gas filters 2 gas filters ....I was tanking out of the gasoline in the fall......now back in the old days are NOT ALCOHOL ....I was my MMO additive gasoline ...93 octane gas ...

 

[Lou C]

Your main fuel filter is in pic #2, extreme lower right, the round housing you see there, the large water separating fuel filter should be screwed into that housing (below what you see in the pic) it is large like an oil filter. Some Mercs had the pump with the filter built in but you appear to have the add on bracket for the larger filter which is better IMO.
There may be another small filter at the inlet for the carb, access by removing the fuel line, be careful use fuel line wrenches so you don't strip the nuts, and also make sure to not cross thread the fitting when reinstalling, if you do change that one. If it's a Quadrajet (4bbl) that filter is really just a screen, the big filter is the one to be concerned with. Not sure if the 2bbl was the same.
Be careful with that large filter it will be full of gas. I like to dump them out in a Mason jar to inspect the fuel. Mine is usually clean so I just dump that in the gas can for my lawn mower. When I replace these I fill it about 3/4 full with fresh gas (carefully) and then lube the o-ring with motor oil, get it on hand tight, not crazy tight, (3/4 turn after the gasket seats is the official spec) or else it might be hell to remove next year. These should be replaced yearly.

to get at the anti siphon valve, you have to find the access to the top of the fuel tank and fuel level sending unit. Either there is a hatch that comes up or a small circular plate that is removed.

 

[minj]

Your main fuel filter is in pic #2, extreme lower right, the round housing you see there, the large water separating fuel filter should be screwed into that housing (below what you see in the pic) it is large like an oil filter. Some Mercs had the pump with the filter built in but you appear to have the add on bracket for the larger filter which is better IMO.
There may be another small filter at the inlet for the carb, access by removing the fuel line, be careful use fuel line wrenches so you don't strip the nuts, and also make sure to not cross thread the fitting when reinstalling, if you do change that one. If it's a Quadrajet (4bbl) that filter is really just a screen, the big filter is the one to be concerned with. Not sure if the 2bbl was the same.
Be careful with that large filter it will be full of gas. I like to dump them out in a Mason jar to inspect the fuel. Mine is usually clean so I just dump that in the gas can for my lawn mower. When I replace these I fill it about 3/4 full with fresh gas (carefully) and then lube the o-ring with motor oil, get it on hand tight, not crazy tight, (3/4 turn after the gasket seats is the official spec) or else it might be hell to remove next year. These should be replaced yearly.

to get at the anti siphon valve, you have to find the access to the top of the fuel tank and fuel level sending unit. Either there is a hatch that comes up or a small circular plate that is removed.

Thank you very much, this is good information. I will have a look at all this when I head back there!

 

[minj]

Yes, maybe it's coming up as a 1988 - 1992
Can have a 2BBL or 4BBL carb
2BBL Merc carb filter item 29
https://www.mercruiserparts.com/bam/subassembly/31478/951/110

4BBL Rochester carb filter item 8
https://www.mercruiserparts.com/bam/subassembly/31478/951/130

Combo Fuel pump and filter is on the block
https://www.mercruiserparts.com/bam/subassembly/31478/951/90

Good day!
I went back to the boat and changed the big fuel filter because it was easier, I cleaned the tank vent on the side of the boat (it had a spider nest), and put seafoam in the gas tank. (half a bottle).

I cannot get the boat out of the water, I'm almost vertical and it wont go out, stuck at 3200RPM and it appears to have not the full power. Finally the the throttle is fully down when doing that and then it loses power to almost stop the engine.

At idle or 1200-1500 RPM it runs fine.

I am attaching 3 pictures.
1- gas that was in the fuel filter
2- inline gas on the carb before removing the male fitting with clear hose in the way
3- same thing but the male fitting removed
4- motor sound (full throttle) goes from 20 to 22. RPM

I cannot remove the 2 fittings where the gas line go in. The nut is completely destroyed (round), I guess the previous owner changed that filter a couple times. I am waiting on monday to go buy those 3 fittings (including the one I have remove.

Are there any tools for that because that male fitting there (not sure what it is for (vapor?), was quite hard to remove. it is almost touching the carb and below that there is that black hose and fitting iside it. I have no room to work...

The 2 links you provided for the carb doesn't appear to be like the one I have. It's a 4BBL but where the filter is it's different. I went to the part shops and they sold me the short paper filter. (owner also told me about that paper filter)

Thank you for any more tips!

ps: according to owner, the fuel pump was changed, boat was parked for almost 2 years.
edits: added motor sound

 

[Scott Danforth]

Are there any tools for that because that male fitting there (not sure what it is for (vapor?),

The tygon line comes from the fuel pump. If the pump fails, it pump the fuel to the carb vs dumping into the bilge and blowing up

ps: according to owner, the fuel pump was changed, boat was parked for almost 2 years.

After 2 years, you need to clean the whole system including the tank.

The fuel in your pic has debris in it

 

[alldodge]

Use vise grips or small pipe wrench on fuel line to remove. Hole other nut with another wrench. Replace line with new brake line. Fittings will be the same

Looks as fuel has gone bad, so it needs to be pumped out and disposed

 

[minj]

Use vise grips or small pipe wrench on fuel line to remove. Hole other nut with another wrench. Replace line with new brake line. Fittings will be the same

Looks as fuel has gone bad, so it needs to be pumped out and disposed

Thanks - The tank was almost empty when I refill it with around 20 gal. Does that mean I lost that 20 gal?

 

[minj]

The tygon line comes from the fuel pump. If the pump fails, it pump the fuel to the carb vs dumping into the bilge and blowing up

After 2 years, you need to clean the whole system including the tank.

The fuel in your pic has debris in it

Thank you, would I be able to prevent myself from doing a whole cleanup by doing small things while the boat is in the water?

 

[alldodge]

Gas should be clear, yours looks yellow.
Does it smell like gas?

As Scott said there is a lot of crud in the filter
It could be the old gas was just in the filter and not in the tank. If you dump the filter again and it still looks the same yellow then maybe it's lost. Don't know your call

 

[minj]

Gas should be clear, yours looks yellow.
Does it smell like gas?

As Scott said there is a lot of crud in the filter
It could be the old gas was just in the filter and not in the tank. If you dump the filter again and it still looks the same yellow then maybe it's lost. Don't know your call

What's weird is we did tried the boat with the owner and we had no problems for a 5 minutes ride.

Brought it to our place, ran it for 5 minutes, did well then, started to do what I've said starting this post.

To be honest the smell was a little weird when I first removed the filter, it did smell gas but did smell something else. Not sure how much gas was in the tank but good idea. I could check the gas in the filter again. (but I did fill the fitler to 3/4 with new gas.

 

[Scott Danforth]

Sitting for 2 years anything in the tank would have become goo.

 

[minj]

Use vise grips or small pipe wrench on fuel line to remove. Hole other nut with another wrench. Replace line with new brake line. Fittings will be the same

Looks as fuel has gone bad, so it needs to be pumped out and disposed

If I replace the fuel line, does it come premade with the fitting or I have to do it myself (the bending and connectors)?