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Mercury 90 hp losing engine power

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marclubs

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Newbie here!!! I bought a 90 hp 1989 mercury outboard, when running at 3/4 or full throttle, it seems too run out of gas, RPM's slow down too even idle speed. If I bring it down too idle speed engaged and run a few minutes, I can take off again and am good for 10 to 15 km, then it starts acting up again. The owner changed all the filters. I am thinking it might be the fuel pump. Anybody have that problem before!!! Thank you...
 
I am not a professional on outboards but maybe i can lend a thought or two... It does sounds like fuel starvation.. If the fuel filter is directional... sometimes they are and that could be the culprit and i would ensure that the hoses were put back on to the correct places..

If you rev the motor in neutral does is rev down rather slowly? like slower then you would expect? In most cases when lean for fuel revs come down very slowly .. you may not be able to get this symptom until you run it like you have to get it to act up then right after you get it to idle try revving it in neutral to see if that's the case.... wont tell you much but confirm that fuel starvation is the issue..

Sorry i couldn't help more but there are some very knowledgeable people on this site and they will deff be able to have some input.

-tim
 
Fuel lines may be swollen internally; if the squeeze bulb pump goes flat when it occurs check the vent, the pickup tube, the antisipon valve at the top of the tank. If opening the gas cap a little helps then tank vent is blocked. If all is good then inspect/rebuild the pump w/a Merc. kit and not a Sierra kit.
 
marclubs said:
Newbie here!!! I bought a 90 hp 1989 mercury outboard, when running at 3/4 or full throttle, it seems too run out of gas, RPM's slow down too even idle speed. If I bring it down too idle speed engaged and run a few minutes, I can take off again and am good for 10 to 15 km, then it starts acting up again. The owner changed all the filters. I am thinking it might be the fuel pump. Anybody have that problem before!!! Thank you...
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I have a 90 HP Mercury on my pontoon a 2002 and never had a problem. I go 2900 RPMs and my 2 stoke runs fine, but when I excellerate over 2900 rpms it puffs short puffs. With a little more rpms it stalls right out it puffs more then when I try to extend the rpms to full throddle it stalls out! (Any Answers??) It is a three cylinder. I just changed the fuel filter, plugs, starter motor and cellinode. I bought new plug wires but have not put them on yet. Are we talking the Carbs or Gas problems Please advise Thank You Garry
 
I have a 2002 3 cyclinder two stoke 90 Horse Mercury and it runs fine up to 2900 rpms but 3000 rpms it starts to puff every few seconds then when I advance the throddle to more rpms it puffs more often. When I try to go full throddle it stalls out. I have changed all the usual suspects but to no avail any Ideas?? Thank You Garry
 
What did the old spark plugs look like? It may not be firing on all 3 cylinders. Carbs may need rebuilt due to fuel varnish buildup.
 
Gonna have too wait till the snow leaves, but will probably end up cleaning the carbs and changing the plugs and checking the fuel lines. Thank you
 
The old plugs did'nt seem bad but I changd them anyway. A little darker but not bad. Do you think a compression check might be good to determine the compressure of each cylinder?
 
garrylvball said:
The old plugs did'nt seem bad but I changd them anyway. A little darker but not bad. Do you think a compression check might be good to determine the compressure of each cylinder?
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Racerone is right on in first step is compression in 2 stroke diagnostics. One of the big 3 compression, lower unit, spark. As for your problem it certainly sounds like classic Mercury Ignition Stator fail (on high side).
 
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