Merc 90 loss of power

[neil.mccrirrick]

Ok, thanks all, I'll chop the valve out and connect directly for now. Re the fuel lines nothing is brittle yet, but I think its a good idea to change anyway as all the seals look and feel tight.

Any recommendations as to where I can source 10 feet or so of fuel line?

The more I think about it though the more I think its an air lock somewhere. But I can't see how. The engine died half a dozen times on the way back from Piel, starting each time when I pumped the bulb, but the bulb struggled to reinflate.

The bit I can't fathom, is that it happened on both tanks, the vents were open on both and on the main tank, I unscrewed the cap, no sound of gas escaping etc, and it made no difference, i.e once the carbs emptied we stopped again.

So maybe crap in the main line to the outboard, that is stuck due to that plastic valve or collapsed line, but if the line is collapsed you would think I would have had it on the way out, (less fuel in the tank can't make a difference surely).

Anyway I'll take the plastic valve off and blow through, fingers crossed a big lump of crap will come out and all will be good. Failing that I may be doing some stop starting on Paul's Easter run at Anglesey

[matt h]

it sounds like the fuel pick up pipe from the tank to the many connections
either collapsed or something trapped in the connector causing continuing cutouts when the fuel pump cant suck any more
once left and primed all ok until the repeat happens again

i had this happen to me, load of paper in a brand new fuel tank, fine for 30 mins until cut out,every 3 mins then cutting out.... i was in rough seas at the time so had to manually pump fuel through to keep me out of trouble,#

the crap had gone up the the fuel tank elbow so had to clear the lot.

"but if the line is collapsed you would think I would have had it on the way out"
No as it takes time for the pump to say ,, ive had enough!!

[9D280]

Two thoughts:

I too have had problems mixing Plastic & metal connectors. I got the opposite problem - they wouldn't actuially mate! Not a leap of logic to assume if you are the other way round an air leak is likely.

Also as a sanity check, what ID is that fuel hose? When I swapped form my old Suz 25 to the Yam 55 (the Merc's predecessor) Al lI did was change the connector on my tank. The Suz ran fine on the 1/4" hose, but the yam couldnlt manage more than about 3-4 mins before it coughed & stopped. I re- hosed the entire setup with 3/8" and the problem went away.

Now, if you have a 3 way valve and various other things in your line, could you be restricting the flow just enough to cause problems at WOT? I only had about 3/4 metre of 1/4" hose and that was enough to stop a 55HP.

[neil.mccrirrick]

Hose is 3/8ths and it was fine all last season with that so I think I'm ok there.

Stripped everything down today, both fuel tanks out and blown through all the hoses, (and took the time to clean out the main tank, bit of debris in there, but not much.

Haven't found any failure points in the hoses. Chopped the grey valve out so that's good.

I have found one peculiarity though. The primer bulb is quicksilver as mentioned earlier. connected the right way. When I blow through one way it works as it should, and when I blow the other it stops, so all good. BUT I've used the bulb with a length of hose to empty the main tank into a container to clean etc, and it seems to work intermittently, i.e. it won't always drag fuel through. I have a chap backup bulb that is brand new, (keep it in the boat just in case), and that pulls fuel everytime.

I can't find a leak anywhere in the quicksilver one, nor perished, when I blow as hard as I can, blocking the ends no air escapes, but still very odd.

So I've ordered a new one, and I'll put the cheapo one on for now and see how it goes.

Can they break down inside? Can't get in it without destroying it, which I will do when the new one arrives, to see.

[neil.mccrirrick]

Following all the help I received here, I found this article, which I've edited slightly to serve as a troubleshooting guide:

Standard outboard fuel pump troubleshooting (All brands/models)
There isn't really too much involving fuel pump troubleshooting. If you feel though the fuel pump is your problem, read on.

A standard outboard fuel pump is a simple device that operates off the pulse of an engines cylinder. A basic rubber fuel line connects the fuel pump to a pulse valve (some models of fuel pump attach directly to the block with a gasket, sealing pulse passage to cylinder), which is normally threaded into the block with provisions of a clear passage to a specified cylinder. The up and down stroke of the piston in the specific cylinder is what causes the fuel pump diaphragm to flutter, resulting in pumping fuel from tank to carbs.

So how do I know the fuel pump is doing what it is suppose to?
As described above, the fuel pump requires an adequate pulse from the cylinder that it is attached to, so first thing is to make sure compression on that cylinder is up to snuff or the fuel pump can't do it's job. If compression checks out, then next thing is to check fuel pump pressure. All non fuel injected outboard motors operate with a fuel pump pressure of about 5 to 7 psi. If considerably less than 5 to 7 psi exists between fuel pump and carb/s, the motor is likely to be starving for fuel causing idle and/or upper rpm operation to suffer, not to mention a dangerously lean condition.

So what if everything to do with pulse supply to the pump is good, but I still suspect the pump has a problem?
It is possible for either the diaphragm, check valves, or other problem to develop in a fuel pump. If it's plainly worn out, then so be it, install a kit or replace pump entirely, but I would suggest checking all other things in this troubleshooter page before just taking it for granted your time and money spent on a fuel pump kit or replacement pump will solve your motor's woes.

Could anything else cause the fuel pump to not provide adequate fuel supply to the motor?
The answer is yes. There could be a restriction or loose connection from tank to fuel pump, amongst other things. Assuming you have no leaks (including pinholes in hoses) anywhere in-between, the following would be things to check for:
• Fuel tank internal pickup tube clogged, broken off, or otherwise defective.
• Anti syphon valve located on tank (if so equipped) could be defective (check ball/spring).
• Any kinked hoses between tank and pump.
• Defective in-line squeeze bulb (usually the internal check valve).
• Defective or incorrectly attached fuel line connectors.
• Clogged fuel filter.
• Inadequate fuel tank vent or kinked vent hose.
• Degraded fuel line


I'm still not 100% I've resolved all my issues, (despite following all this and advice given here, and sage advice from Uncle Al, via PM), as the only way to test is in the water and under load. But no matter what, it will be one of the things listed above. If I'm wrong please add to this, for others that will no doubt have issue at some point.