50 HP Mercury 2-stroke losing power at wide open throttle

5/26/14 @ 9:32 PM
ORIGINAL POST
CazTrait
CazTrait
USER since 6/15/01
Like the title says, 1999 50 HP Merc 2-stroke losing power at wide open throttle. Things that have been suggested from bar stool Merc techs: fuel filter, fuel pump, fuel line/primer ball. What I know... Primer ball in the fuel line seems to be holding firm. First time I pumped the ball this weekend it didn't "release" and stayed compressed. Didn't have a problem like that after the first pump. First time this happened I was running WOT approximate 30 seconds and the motor died as if I pulled the kill switch. Kill switch was not pulled and in the run position. Could not restart immediately. Checked plug wires and fuses, everything OK. Idled fine prior and continued to idle fine, wouldn't die at idle RPM's. Approximately half throttle, it bogs a bit and seems to not be getting full power. Boat/motor doesn't want to "pop" on the hole shot and plan out like usual. Seems to be starving for fuel as if the primer ball isn't firm, but the ball is firm. Day two this weekend, idled around fine in the morning. When I was done fishing, I did the test run back to the launch. Same thing, motor died at WOT after approximately a minute. Good water pressure, no over heat alarm. I was having issues with low pressure and over heating two years ago and replaced the impeller at the start of last year which resolved the issue. Fresh gas, had approximately a gallon left from last year, but topped off with 9 gallons of fresh fuel this year. Ran seafoam through the motor last year, only put 2 tanks of gas through it last year. What I don't know (yet): Condition of the carb, fuel pump or filter. Compression at the plugs (plugs look fine and were replaced last year or year prior, I only run the motor approximately 20 hours a year) If any of you Lake-link brain trusts were to start throwing parts at it given all the information above, where would you start? Fuel pump? Fuel line/ball? Fuel filter? Carb? Appreciate any help or advice you guys can offer.
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Displaying 1 to 10 of 29 Posts
12/1/16 @ 7:42 AM
Shellfish
Shellfish
USER since 7/19/03

Had an almost exact same problem with 1990's 15 hp 2 cycle johnson.  Lost power at 3/4 to full power and would stall.  This was a first time new problem.  The motor had always run great previous.  Noticed small gas leak at hose to engine connector.  Replaced all gas line and bulb and connectors from portable gas tank to engine.  Problem solved, runs like brand new.  Hoses, connectors, bulbs, check valves and gaskets just wear out over time.   Simple and not to expensive of a fix.

Good luck, Shellfish

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11/1/16 @ 6:39 AM
Fishlovme
Fishlovme
MEMBER since 6/22/01
Well, I opened the hood on my motor the other day, just to see if I could find any fuel line leaks of any sorts.  I did smell gas immediately. Looked around and didn't notice any sort of leaks in the fuel line, so if there is one there it's pretty small.  I did open the carb cover and there was quite a bit of gas on one of the three holes.  Think I found the problem there, one of the gaskets had fallen off and was inside of the cover.  Another one of the rubber gaskets is cracked a little, so I don't have a good seal to that carburetor cover.  Not sure if that's one of my problems or not, as I believe all that cover does is help with emissions, but I'm not motor expert.  Thoughts, anyone?

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10/14/16 @ 6:37 PM
Ed Franko
Big Ed's Guide Service
USER since 5/6/15

Your fuel line might be coming apart from the inside because of the ethanol in the gas. I had that problem before. The gas line looks great but on the inside is where the problem is.  See of you could borrow a take and a hose from somebody and give that a try.. I use Mercury quick clean in my motor a little goes a long way.. Don't over do it.Hard to tell a man Folllow the directions.. Is that a Oil injector motor if so might want to check your oil level and make sure the lid is tight..

Edited on 10/14/16 6:38 PM
Big Ed’s Guide Service
(573) 692-6710
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10/13/16 @ 6:33 PM
Plmlk
Plmlk
MEMBER since 12/18/07

Pike Eyes-

I know what you're saying...

I've manually closed my vent while transporting the tank, and when I opened it there was pressure. 

The vented gas caps act as a check valve of sorts...

When a negative pressure is present, the cap has a flapper that opens to allow air in - under a neutral pressure the flapper is closed. 

I would imagine a positive pressure would would likely press against the seat (flapper) causing it to seal. That is why (in my opinion) a manual vent is the way to go - nothing to break.  Without a vented outboard tank you'll experience intermittent engine shut-downs, and the bulb mysteriously imploding phenomenon lol


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10/13/16 @ 12:19 PM
pike eyes
pike eyes
USER since 12/28/10

PLMK , You may be right but I'm still doubtfull because when I take the cap off sometimes there is alot of preasure in the tank. Especially on hot days when the tank is getting low on gas? If it were vented this wouldn't be happening.

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10/12/16 @ 5:07 PM
Plmlk
Plmlk
MEMBER since 12/18/07

Pike Eyes-

You likely had a self venting cap and did not realize it - they are fairly common.

Pumping the bulb simply gets the fuel to the fuel pump when the motor is not running so the engine can start.  After the engine starts, the fuel pump takes over and sucks gas from the tank.  If the tank is not vented, the engine will starve for gas and quit.  I had an old tank with a self venting cap that did not work, I had to loosen the cap while the motor was running or it would starve for fuel and quit. 



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10/12/16 @ 11:48 AM
pike eyes
pike eyes
USER since 12/28/10

not saying he is wrong, but not all motors run on a vented system. My 50 Evenrude [2 stroke] is a sealed system. Tanks dont even have a vent. Some of the newer tanks have that to relieve the preasure on hot days when your lower on gas levels,but run on a sealed system. Google your motor for factory recommendations. Good luck

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10/12/16 @ 7:53 AM
Fishlovme
Fishlovme
MEMBER since 6/22/01
I agree with the Seafoam comment.  I use it in all of my motors - snowblower, lawn mower, outboard motor, ice auger, and the trimmer.  I always buy premium gas with "no ethanol" as well (I parenthesis that because I'm pretty sure they can't remove all of the ethanol, especially since a lot of the pumps at the gas station use only one line!) . It may cost just a little more but Ethanol gas is not good for these motors!

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10/11/16 @ 4:51 PM
Plmlk
Plmlk
MEMBER since 12/18/07

Also, for anyone running older motors with ethanol fuel, you absolutely must add a fuel treatment / maintainer. 

For keeping things clean and stabilizing the fuel, I really like Seafoam - magic in a can!

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10/11/16 @ 4:48 PM
Plmlk
Plmlk
MEMBER since 12/18/07

Fishloveme-

The vent on the gas tank you are referring to should always be open.  It is a similar concept to sucking on a straw, if you put your finger over the other end the suction stops.  If you remove your finger it returns.  The vent on the tank has to stay open or you will starve the motor for fuel.

The leak I am referring to is after the tank, in the hose, bulb, or fuel line downstream.  If you pump your bulb and it does not stay firm - you have an air leak, or a bad check valve in the bulb.  Since you replaced the bulb already, your issue is likely between the bulb and the fuel pump. 


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