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Thread: Mercury 40 HP problem....HELP!!

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    Default Mercury 40 HP problem....HELP!!

    I think I may have posted about this once before, but it's back, and worse. I have a 2002 Mercury 2 stroke 40 HP with auto oil injection. When I run in low RPM, it dies or runs really sluggish. I had this issue before and was advised to idle it up, which I did, along with changing the plugs and it seemed to work, but now the problem has returned. Only now I have trouble getting it refired when it dies. I have to put the throttle at least half way(in neutral of course) to get it to start sometimes after it dies or after it sits off for a while when I shut it off to fish. Also, late in the day last time out the motor ran extremely sluggish even throttled all the way. Almost like the boat was really loaded down. I took the plugs out today and found the lower plug had quite a bit of oil on it. I cleaned it off and plan to change both along with the oil filter, but I can't figure out why they keep fouling every six months or so. Is it because I need to run a higher grade gas? Could the oil injection be adding too much oil? Not enough gas through carb? Is there a carb cleaner that I can run through it that works at all? Sorry for all the questions. I really don't have the funds or time right now to take it to the shop. If it's something short of tearing the carb apart I can probably do it. Please help.

    By the way, I use regular grade gas and Pennzoil Marine XLF oil, if that matters.
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    Cane Pole's Avatar
    Cane Pole is offline Crappie.com 2011 Man of the Year * Crappie.com Supporter
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    Quote Originally Posted by SpeckWick View Post
    I think I may have posted about this once before, but it's back, and worse. I have a 2002 Mercury 2 stroke 40 HP with auto oil injection. When I run in low RPM, it dies or runs really sluggish. I had this issue before and was advised to idle it up, which I did, along with changing the plugs and it seemed to work, but now the problem has returned. Only now I have trouble getting it refired when it dies. I have to put the throttle at least half way(in neutral of course) to get it to start sometimes after it dies or after it sits off for a while when I shut it off to fish. Also, late in the day last time out the motor ran extremely sluggish even throttled all the way. Almost like the boat was really loaded down. I took the plugs out today and found the lower plug had quite a bit of oil on it. I cleaned it off and plan to change both along with the oil filter, but I can't figure out why they keep fouling every six months or so. Is it because I need to run a higher grade gas? Could the oil injection be adding too much oil? Not enough gas through carb? Is there a carb cleaner that I can run through it that works at all? Sorry for all the questions. I really don't have the funds or time right now to take it to the shop. If it's something short of tearing the carb apart I can probably do it. Please help.

    By the way, I use regular grade gas and Pennzoil Marine XLF oil, if that matters.
    I am no mechanic, but fuel fowled plugs tells me you may have ignition problems.

    Also, I had 40 Mariner with similar prob. Cleaned carbs, replaced jets. Fixed it.
    Last edited by Cane Pole; 06-15-2008 at 09:36 PM.
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    I have never fouled a plug.The problem is a fouled plug if it has oil on it.Take the plug out and hook the plug wire on and turn it over to see if the plug fire's.If it doesnt change the plug and check before installing.If the new plug fire's I would unhook the oil reservoir and plug it.If the new plug dont fire you probally need a new powerpack.While youre in the middle of all this clean the carb's and reset the float.I fixed one a while back and the problem was his gas tank had a vent valve closed.May be something simple.Try to find it because power pack's are not cheap.
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    Quote Originally Posted by Slipped Cork View Post
    I have never fouled a plug.The problem is a fouled plug if it has oil on it.Take the plug out and hook the plug wire on and turn it over to see if the plug fire's.If it doesnt change the plug and check before installing.If the new plug fire's I would unhook the oil reservoir and plug it.If the new plug dont fire you probally need a new powerpack.While youre in the middle of all this clean the carb's and reset the float.I fixed one a while back and the problem was his gas tank had a vent valve closed.May be something simple.Try to find it because power pack's are not cheap.
    I have never had a carb apart. My fear is if I take it apart and screw something up, I end up spending a bunch of $$ on something that wasn' the problem to begin with. Is this something relatively simple to do? I am pretty mechanically inclined, but new to working on outboards. Also, if the plug fires when I take it out, does this mean I am getting too much oil due to the oil injection system?
    One thing I noticed...This evening I had the motor cover off and started it. I noticed some gas laying in the bottom of the motor. Not a bunch, but enough to get my attention, and I'm sure more than what should be there. Again, I am new at troubleshooting and working on motors, so if any of this seems obvious, remember, I'm a rookie.
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    Quote Originally Posted by Slipped Cork View Post
    I fixed one a while back and the problem was his gas tank had a vent valve closed.May be something simple.Try to find it because power pack's are not cheap.
    Where will I find the vent valve on the gas tank? Again.....rookie.
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    jaxsprat is offline Crappie.com 3K Star General * Crappie.com Supporter
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    Please, no offense but if U don't know where gas vent is/looks like please don't take apart carbs. just make sure gas vent is open & bulb should be fairly hard when motor is running, if thats OK take to mech as it can be pretty easy to mess up carbs & U won't find out if this was problem #1
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    Is it an inboard tank or a portable one?
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    grubby, it's an inboard tank.

    jaxsprat, no offense taken, believe me. If I knew what I was doing or even thought I did, the carb would already be cleaned if not but to eliminate that as a possible cause of the problem. So rest assured I don't plan on taking it apart. I am trying to cover all the simple things it could be before taking it to the shop. As for the fuel primer bulb, when the motor is running, or right after it dies, the bulb is not hard. I can pump it and make it firm again, but as it runs it softens. Man, it's a good thing everyone here knows we are talking about fuel bulbs.....LOL. Sorry. Anyway, what could that mean if the bulb isn't firm while running? Would it have any bearing on the fouled plug or the lack of power, dying. Obviously if the motor is getting air instead of gas it will die or not start. Could it be as simple as replacing the bulb?
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    If you never had a carb apart dont do this one.I guess I got a little techinal about this.I should have explained the float's have to be set to spec's.Most all onboard vent's cant be closed.If you have a portable tank like the one I fixed was a portable.They have a vent valve and if it's not open it wont run long.I would say if the plug fire's the oil may be the problem.As far as the gas in the bottom of the motor goe's the overflow will cause that along with numerous other thing's.I'll give some good advice now,take it to a mechanic.

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    I just had a pretty much identical problem with my 25 HP Merc. It would cut off on me at low speeds, would get bogged down after running a while, and finally got to where it would not run for more than a couple of minutes. Turned out that the motor was not cycling water and was not cooling properly and was causing the motor to seize up, which was an impeller problem. Get a repair manual for your motor ($20-$30) and it will guide you through how to get to the impeller. Check to see if it is worn or damaged at all. However, you really may want to consider saving up a little bit and have a mechanic take a look at the carb as well because they probably need a cleaning beyond what a spray carb cleaner can do. Also, if you take out the plugs to see if they generate a spark, which you should do, MAKE SURE you have the plug grounded against a metal part on the motor. If you don't it'll shock the daylights out of you (speaking from experience). Good luck.
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