Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

[chimmike]

Just rebuilt it. 2bbl Mercarb, 1991, 5.0 V8.

I rebuilt with the solid lifter for the needle valve. One option in the rebuild kit was the sprung lifter for the needle valve. I'm going to try swapping that in as I've run across documents saying that solves the issue, but what else could be causing fuel to basically dump in?

Causes the boat to cough/stutter heavily at ~1500rpm and will not reach any higher revs.

 

[alldodge]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Just rebuilt it. 2bbl Mercarb, 1991, 5.0 V8.

I rebuilt with the solid lifter for the needle valve. One option in the rebuild kit was the sprung lifter for the needle valve. I'm going to try swapping that in as I've run across documents saying that solves the issue, but what else could be causing fuel to basically dump in?

Causes the boat to cough/stutter heavily at ~1500rpm and will not reach any higher revs.

Most common causes for a carb to flood are: Needle seat not seating properly or damaged, Float level not correctly set.

Never heard of a solid or sprung lifter for the needle valve, so I don't know what to say. The needle valvles I worked with and a wire which attached to the back of the needle and which was placed on the float to help pull it open when the float dropped.

 

[Mariah180]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Just rebuilt it. 2bbl Mercarb, 1991, 5.0 V8.

I rebuilt with the solid lifter for the needle valve. One option in the rebuild kit was the sprung lifter for the needle valve. I'm going to try swapping that in as I've run across documents saying that solves the issue, but what else could be causing fuel to basically dump in?

Causes the boat to cough/stutter heavily at ~1500rpm and will not reach any higher revs.

Mines doing the same. It runs fought. When opening the throttle it sucks air as I can hear it. But it won't accelerate. If I pump the throttle correctly I can get it to come off idle and run semi ok at higher rpms. Once In drive its really hard to get it to accelerate. But once its accelerates and comes on plane it will run near 99% correct. Full rpms and power. Even able to slow down and return to speed but once I shut down and then resart its the same hassle of knot wanting to accelerate.

Fuel filter is new. Fuel may be junk as its the old fuel from last year, with some heet to remove water and seafoam fuel cleaner,

I checked the fuel ands its as you described. Drops but not decent spray or stream. Looks ok when the accelerators dumps. I too, the top off the carb and the float/bowl were clean. I've not yet looked at the jets.

Let us know what happens if you find the problem,

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Yeah I swapped over to the sprung lifter for the needle valve, so i'll be testing that shortly, and hope I measured and set the float drop correctly.

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

And I can't even get it to accelerate if I move throttle up SLOWLY, or if I jam it to full. Same problem.

 

[alldodge]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Can you provide a pic of the sprung and solid lifter?

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

http://www.google.com/url?sa=t&rct=...=GQU9FQO7ZyBmDlj3XJx53A&bvm=bv.50500085,d.b2I

it's the second or 3rd page there. Kind of explains the purpose.

I'm almost wishing it wasn't so pricey to just get a different carb at this point. Can't go to autozone and get a 4bbl on a 2bbl manifold :/

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Also came across this http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/mercarb-2bbl-369019.html

 

[alldodge]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

http://www.google.com/url?sa=t&rct=...=GQU9FQO7ZyBmDlj3XJx53A&bvm=bv.50500085,d.b2I

it's the second or 3rd page there. Kind of explains the purpose.

I'm almost wishing it wasn't so pricey to just get a different carb at this point. Can't go to autozone and get a 4bbl on a 2bbl manifold :/

Also came across this http://forums.iboats.com/mercruiser-i-o-inboard-engines-outdrives/mercarb-2bbl-369019.html

Thanks you learned me something today. I see now what your talking about it was the term sprung and solid lifter. If it was spring loaded needle seat and solid two piece needle seat, I probably still wouldn't have got it, but I could have pictured it a bit better.

That being said a flooding carb is controlled by the needle, seat and float level. Did your kit come with a new float, if not does it feel heavy? The float should be real light, is it metal and hallow or composite?

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Didn't come with a new float. This float is hollow plastic. I also found something that recommends a quicksilver part number for a 2.5mm opening needle valve rather than the 3mm stock needle. Hmm. And recommends a newer venturi, and something else.

 

[alldodge]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Didn't come with a new float. This float is hollow plastic. I also found something that recommends a quicksilver part number for a 2.5mm opening needle valve rather than the 3mm stock needle. Hmm. And recommends a newer venturi, and something else.

Since it's dumping fuel maybe the new venturi is an idea. I asked about the float because many start sinking. Have you tried setting the float lower the required so the bowl will have less fuel (just spit balling)?

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

That's a good idea. Worth a try.

Went and water tested, no-go. Coughing and sputtering in the same place as before. Thinking of getting a new cap and rotor, and new plug wires for the thunderbolt IV.

Seems that this only happens under load.

 

[bonzoscott]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Is it dumping fuel while running or not running? Are you saying you're looking down the carb while running and it's pouring fuel out of the venturis or idle port. I'm thinking fuel pressure if you rebuilt carb including needle and seat. Float level set right? Spring loaded needle is generally for bouncing around like on a motor bike. If you use the spring loaded needle, do not compress the spring when setting float level. I feel like that application is something the manufacture through at customer complaints. The stern of an I/O doesn't bounce that much unless you're WOT over large wakes.

 

[NHGuy]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

You can't go wrong with cap, rotor wires. If they are of unknown age & condition they are usually a smart thing.
BTW thanks for that carb link, it was informative. Fills in some gaps in my mental library.

 

[Mariah180]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

That's a good idea. Worth a try.

Went and water tested, no-go. Coughing and sputtering in the same place as before. Thinking of getting a new cap and rotor, and new plug wires for the thunderbolt IV.

Seems that this only happens under load.

When not in gear will the engine accelerate normally?

 

[midcarolina]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

When you had the carb apart did you check the power valve actuator to make sure it is free and not froze....

The actuator not working properly will cause a very bad flat spot in the throttle

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

When not in gear will the engine accelerate normally?

yes, revs normally when not under load. On mouse ears in gear it will accelerate normally.
on the water not in gear will hit 4000rpm.

Only does this under load in the water. That's what is stumping me.

Bonzo: It's dumping fuel from the venturis, but not as much since I did the spring actuated needle valve.

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

http://www.google.com/url?sa=t&rct=...=GQU9FQO7ZyBmDlj3XJx53A&bvm=bv.50500085,d.b2I

Pages 3 and 4 of this link also recommend a 2.5mm needle valve and a new venturi cluster. I am not certain the needle valve is my problem based on the symptoms posted. It idles smoothly enough but with an occasional miss that I've attributed to compression numbers ALL OVER THE BOARD on this motor (it's 22 years old has a couple cylinders with terrible compression).

 

[chimmike]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Any other thoughts?

 

[alldodge]

Re: Mercarb 2bbl dumping fuel >1000rpm (visible drops/flow, not spray)

Pages 3 and 4 of this link also recommend a 2.5mm needle valve and a new venturi cluster. I am not certain the needle valve is my problem based on the symptoms posted. It idles smoothly enough but with an occasional miss that I've attributed to compression numbers ALL OVER THE BOARD on this motor (it's 22 years old has a couple cylinders with terrible compression).

You have done your home work and according to the bulletin if your carb is still flooding, and it is, only thing to do is get the 2.5mm seat. With that you brought up an issue which has a large impact on running and performance. You mentioned the compression test has readings all over the board. The compression can cause missing but also inability to pull it's self out of the water due to insufficient power. This can result in over rich mixture, but even low compression will not cause flooding. After fixing the carb you may be lookin at the engine before long.