Fuel issues with Merc 50hp - need hints please

[bdm56]

Bought a 2nd hand 2003 3cylinder Merc 50hp for my 4.2m Quintrex about 6 months ago. Checked compressions before purchase and had around 150psi with ony a 3 pound spread.

Motor started, ran well through entire rev range for the 1st 6-7 days out. This involved 3 or 4 hours operation per time. Then motor was hard to start from ramp (cold) on next trip, had to crank for what seemed like forever. Once it fired was fine but didn't want to idle reliably, though would only occasionally cut out and stop. Idling bout 800rpm.

This idle problem hasn't changed but the last 2 outings it is developing further problems with I assume the fuel system. It is now starting to (at times) lose power as if it is starving for fuel. The last trip it was ok at the ramp and started after a relatively short crank over, then a run out to the channel of 5 mins planing at 4500rpm crisp and normal then over 30 seconds or so loss of power down to the point where full throttle produced just enough power to keep her on a slow plane. Stopped and let her idle and cut out. Fired normally but remained on 1/2 power for ages (2klm's). Stopped and drifted throwing rubber things around for 15mins then started with engine back to normal.

Problem seems to relate to higher speed operation though not always as came back to ramp with 20mins running on crisp full powered motor.

I have a fair degree of mechanical knowledge from trade years but not familiar with multi cylinder 2 strokes. Before last trip I checked mixture settings on each carb as some symptoms reminded me of lean mix (10 years since last worked with 2 stroke outboard). Screws were about a 1/4 turn in from where I felt they should be, corrected and this produced better starting and smoother idle but as this was before the latest run is more probably a symptom rather than the source of the problem.

Not sure about the fuel line as the fuel bulb sometimes will not pump up hard, just keeps pumping staying soft. When this happens engine still starts normally.

Any ideas ?

In my mind possibilities are:

Fuel pump
Fuel line assembly

Things Checked so far:

Fuel filter in tank
Bulb is pumping strongly
Mixture (11/2 turns out approx)
New fuel






[/list]

[blaze]

check all your connections, maybe air ingress or possible lack of venting
cheers
blaze

[bdm56]

Blaze

Yes have thought of this and have screwed the vent right out on the tank, no difference.

Went over all connections already and nothing obvious, also wouldn't air ingress be reasonably constant ?

[blaze]

agree that it would be fairly constant but there is the chance of fuel line moving with viabration of motor, steering the motor etc. Is the fuel line stiff/old as they are more prone to problems than a nice fresh line and bulb
Bulb? not the one way valve playing up
only thinking to my self at this point
does sound fuel related.
cheers
blaze

[bdm56]

Thanks for the input :) The fuel line is 3 years, same as motor and is still reasonably flexible and yep I was wondering bout the one way too. How long are the bulbs supposed to stay hard after priming and do they go soft ( no comments ;D) after the engine fires and the fuel pump begins to work ?

The tank and line are the original Quicksilver units and are both appear to be in pretty good shape.

[Sea-Dog]

Let me start by saying that I have almost zero experience but........

Could it be some sort of cr@p that is being sucked into fuel system only at high flow conditions (WOT)

I had an old ford econovan that suffered similar symptoms (going uphill, low gear, high revs). It would just die.

Turned out to be a fuel filter full of gunk. @ lower engine speeds it got enough fuel, but high loads and it starved.

When reading your post I immediately pictured something loose floating around in the tank/hose that would mostly block off the fuel flow at high flow, then drop out of the way again when engine off or at idle.

I'm probably wrong, but what the heck - stranger things have happened.

Is there a way to safely blow compressed air in reverse direction to fuel flow to see if anything is living there that doesn't belong?

I'm just thinking out loud. :-/

Cheers

[finga64]

when it's playing up have you tried to pump the primer bulb to see if that helps??

[murf]

has it have choke issues?

[ahoj]

Possible lift pump and its valves not fuctioning correctly Lft pump diaphragm it sounds like short supply to carbies check fuel hoses and fittings any spill of fuel in under the motor?


Ahoj

[bdm56]

Sea-Dog
No loose stuff as far as I know.

finga
yep have tried that and doesn't seem to make any difference which is what made me think the fuel pump could be involved.

murf
No choke issues

ahoj
I thought the same, is there anyway to test the diaphram or do you have to get a kit and take the chance ?

Any outboard mech's on here to give an answer on this one ?

Also how long do your fuel lines stay primed after you pump the bulb till it's hard ?

[nuffy]

i have a fifty yamaha doing the same thing, have swapped fuel pumps and no luck.Have had the carbies off and cleaned, new plugs,new manifold gaskets,new prim pump,new fuel hose, new fuel hose conecters,new fuel filter and still does it.Its wrecking my head as it is the outboard mechanic, but its so spiratic and when he does all the voltage etc checks everything seems fine, but under load it plays up<cant tank test as on stradroke island and mech has limited workshop facilities>just when you lean toward thinking its fuel it cuts out severly like electrical misfire. But then it will run perfect for 5 mins or so and now the weather has come good<2-3knots in the morning bugger>hopefully we both have the same problem and someone can shed some light on it for us.tony

[Spaniard_King]

Sea-Dog


ahoj
I thought the same, is there anyway to test the diaphram or do you have to get a kit and take the chance ?

Any outboard mech's on here to give an answer on this one ?

?

get a gauge that will read up to 10psi put it inline from lift pump to carbies. Run the engine and you can monitor the fuel pressure to the carbies #should be 1-2psi minimum morelikely to be 4 psi #Anyway this will certainly let you know whats happening in that area.

best way is to get a tee piece (brass) and some fuel hose just tee into the hose from pump to carbies. It's easy to do

Garry

[bdm56]

Interesting nuffy, how old is your unit ?

I was thinking of carb cleaning but I was a trdesman in the car industry for 28 years and while this may be an intermittant problem in my case load doesn't seed to be the issue. It seems to be related to rev's with an effect from heat added (I suspect).

In your case I would be looking at electrical breakdown.

Spaniard_King

Unfortunatly I don't have a pressure guage suitable for fuel, but will try at the weekend to get access to one.

Anyone else with experience able to guess this one ?

[nuffy]

my yamaha in mention is a 2002 model.I have only just bought it, has been sitting around for a bit which i know is not good for them, but as you did i also done compression test check of oil in leg and check of plugs all seemed ok and ran well.

[BilgeBoy]

Hey Nuffy

I have a 2002 Yamaha 50 and its going good as....if you want me to check anything for you...you know like compare anything...I can see what I can do.

bdm56
Dont rule out spark etc....Have you got the right heat range plugs, Have you got a clean ignition feed??. Remember you can have voltage without amps!! and the old rule of thumb is POO in POO out when it comes to coils. Hows ya fuses, battery terminals AND EARTHS. You could try running a fresh wire to the coils etc??

If you have pumped the bulb whilst its running and it keeps doing it...you have to think that this would overcome a supply issue. Who knows...I sure feel for ya...nothing worse!

Best of luck with it fella :-/

Regards

Megsy

[bdm56]

BilgeBoy
just rewired entire boat, new battery connections to motor clean, new plugs from merc dealer, coils - hmmm, 3 of em and motor is still very smooth running when problem is present.

Keep coming back to fuel system cause problem is like it's starving for juice but only at times.

Don't know much about stator assembly, maybe a prob with it ? :-[

[Angla]

Nuffy, Definitely look at electrical connections. Could also be a cable working its way out of a crimp or a connector with a pin pulling out the back. So a little pull on cables would be a good test. If it is a big earthing cable, give a good pull but if they are smaller cables just remember to use a little less weight.

Chris

PS. sorry no thoughts for your problem bdm56

[nuffy]

thanks megsy for your offer.Chris have checked all the wiring and conections its a manual 50 no trim tilt or elec start, so shes pretty basic, all looks ok, i thought that to,something earthing out but you can be going flat out and all of a sudden it feels like its dropped 2 cylinders and then othertimes it just hiccups.its a weird one and frustrating im looking out past flat rock this am and its like oil.

[PADDLES]

i'm clutching at straws here guys but some of the more common carby problems with 2s bikes are float and needle/seat valve related. is your float level ok? have you tried something as simple as raising the float level to get a little bit more fuel in the bowl? :-?

[nuffy]

yeah paddles have looked at all avenues with carby and the strangest thing went for a run today and couldnt get it to play up keep my fingers crossed when i go again tomorrow but these things dont fix themselves.

[bdm56]

Spoke with an outboard mechanic today recommended by a mate and he reckons it will definitly be the stator or coil packs.

Will let you know when I have investigated these.

[James_Thorne]

bdm56

I had a similar problem with my 40hp 2st and no one could find the problem. fuel seamed to starve the motor sometimes, yet on other occasions seemed to flood the motor, and bulb would not go hard on pumping sometimes.

Bigest difficulty was that it was intermitent. I ended up taking the carby off, stripping the float shamber down, disconecting the float from the pivot pin, removing the needle that slides into the fuel cut out chamber, geting hold of a jewlers eye magnifying glass and having a good look.

Low and behold I found a tiny egg shaped bur stuck in a slight indent in the chamber. Seems to me that intermitently the bur would roll longways and push the valve needle over slightly to one side not allowing full closure of the needle point up into the seat. As the bur was an odd shape it would vary the seating of the needle. I had to actualy remove the bur using a needle as it seemed to have some magnetic hold onto the side of the needle chamber.

I think the mechanics trying to find the problem may have used air blast to clean it out, this rolled the bur and it worked OK again. And, as it was intermitent, no one looked close enough.

Anyway, problem solved and have had hassle free boating ever since.

Sometimes you just have to do it yourself, and sounds as though you know what your doing.

Hope you get it soughted soon.

Norwestjimbo

[bdm56]

:) For anyone following this thread just wanted to give an update and a warning. Never trust someone else to work on your motor if you can do it yourself >:(

Found my problem and it wasn't fuel. Gave the machine to a "reputable" marine shop in the Springwood area to have a solenoid replaced quite a while back and inspected the job briefly on return with no apparent issues.

Yeah well, whoever did the work actually crushed 2 of the wires which go to the CDI unit when wielding a spanner to replace the soleniod. Not much, just enough to split the plastic right up against the male & female connectors and at the rear out of sight.

Didn't notice this on careful examination of the exterior surfaces when my problem surfaced a while later but went to disconnect and clean every connection and in doing so noticed blackening and heat effects on the other wise soft, new looking wires and connectors on the hidden side. Obviously under some conditions an electrical "leak" was happening between the 2 wires. Guess I'm lucky, the CDI doesn't appear to have been damaged and after a careful repair I ran the motor on the water for 4 hours today without a problem.

Sloppy mongels >:( I am not even going to go near them again as I even discovered 1 of the earth leads to the new solenoid finger tight as well >:(

Have bought a workshop manual and will do all service myself from now on 8-)

And thanks to everyone who gave their 2 bits worth to this one :)

[Reef_fisher]

glad to hear you got it fixed. i had a similar problem with my merc 3cyl 50hp. i was about to suggest cdi. you symptoms were exactly the same as mine. everything that happened was intermittant like yous. the cause showed itself when i did a maintenance run to keep engine in good nick(hadn't used it for a while, anyway, started engine, noticed small amount of smoke coming from where smoke shouldn't. turned out the cdi caught fire. the gunk that they filled it with had split or been damaged some how and the heat did the rest. damn glad i wasn't 30ks out on the reef. mucho dollars later all niggly probs gone, must have been shorting when hot.

[plat-a-puss]

g,day nuffy i have a 04 merc 50 2stroke your prob sounds a little like a prob i had .i do a lot of trolling and on the last outting i found motor wouldnt idle but went great at wot . after a little time motor cleared itself and went fine ,did notice it was a lil smokey . sent motor in 4 service and chatted to mechanic bout problem he said stale fuel (fuel goes off quick these days ,so they tell me) and cause i troll the motor carbons up(causing the smoke).he put a carbon cleaning kit (bout $30) threw motor done usual 200hr service boat has no problems at all now ,no smoke ,idles great
so my advice would b do a carbon clean ,new plugs ,and dont use old fuel