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Thread: Small ob jet missing at wot

  1. #1

    Default Small ob jet missing at wot

    2006 merc 25 efi 4 stroke jet aprox 150 hrs

    bought this motor this spring. Ran great first few times out. Next trip I was cruising and it died on me. Started it back up and it ran fine for 10+ miles. Took it on several trips after that ranging from 10-20 miles, ran great. Next trip was a talkeetna run and it ran fine for about 5 miles, then it started 'missing' at wot. If I backed off to half it would cruise decent, or if I came to an idle, I would be able to go wot for about 15 secs then it would do it again. I also notice after I pulled the hood of that the filter canister was only half full. I limped back home. I changed the spark plugs and put a lil water/fuel step on. I also took the fuel pump off and didn't notice anything with my eyes. Took it to lake and put a bottle of sea foam in with new gas and ran it wot for 30 min, ran great. Problem fixed! Went to rally today and it ran good for about 20 min and started doing it again. Same thing I I backed to half it would cruise. But it's not all there when I'm full throttle. It revs fine in nuetral, and when I do go to nuetral it will run for about 15 secs. It never completely dies on me but something isn't right.

    Im assuming it's the fuel pump, just acts like it isn't getting ennough fuel. The fuel line/primer gets tight when I disconnect from motor, with no leaks. I'm relying on this for my annual Yukon hunt. Before i go buy a pump and continue troubleshooting, does anybody else have any tricks to try? I'm almost positive it is something that is an 'easy' fix. Thanks for your
    time

  2. #2

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    Pumping the bulb while running does not help either..

  3. #3
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    Sounds like you've eliminated the possibility of water in the fuel. I'd take a look at the coils. When you run her wide open for a bit and it starts missing, see if there is a plug/cylinder that is cooler than the others. Coil failures can be pretty intermittent and only show their face under load/heat. Seen it before on the smaller Mercs.

  4. #4

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    Ok i will give that a shot. Why would it only do it ever so often if it was a coil? I mean I ran it full throttle for 30 min on big lake and it ran great. Ran great today for a good 20 min, then outta the blue..

  5. #5

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    You might check your fuel line over real good as you could have a fuel hose separating inside.when you let off it let enough fuel through to run.Mash on it along the full length it might feel soft where it is separating. Good Luck

  6. #6
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    Does the engine have a single coil or a coil for every cylinder? What every the case buy a new one or two and replace them. Do you have a shop manual?

  7. #7

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    Check your plug wires as well. I had a bad one that looked fine but had separated from the plug boot just enough that when things warmed up just enough it would start missing. Changed to new wires and it solved the problem.

  8. #8

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    It has a coil for every one. I'm hoping I may have found the prob. After a lot of googling I think it may be my primer bulb. I do remember stepping on it a while back and that may have messed up the check valves inside it. Last night I was lookin over my fuel lines, and as I was pumping my bulb, I could hear fluid going back to the tank. The bulb would it hard then I could hear gas trickling through it back to tank. Also the lil nipple that my hose
    connects to looks like it has a 'ball valve'. Maybe one of them anti siphoning valves I read about. I was pokin it with a screwdriver and couldn't get it to open...? Also read that these Atwood bulbs are junk, and if they aren't pointing vertically the check calves will not let fluid pass through them. I also need to get rid of my 'grey' fuel hose. As I don't think it is ethanol compliant. Gonna switch out the easy stuff and run a tank through her

  9. #9

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    If you are not taking the boat to the lower 48 you do not have to worry about ethanol as we do not have that up here.

  10. #10
    Member Frostbitten's Avatar
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    Quote Originally Posted by Big Bend View Post
    You might check your fuel line over real good as you could have a fuel hose separating inside.when you let off it let enough fuel through to run.Mash on it along the full length it might feel soft where it is separating. Good Luck
    This is the first thing I would look at as well. If it were me, I would change out the entire fuel line. It's a process of elimination.

    update...sorry, I just saw that you are already doing this. I'm thinking this will solve the problem. Good luck to ya!!

  11. #11

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    Quote Originally Posted by Big Bend View Post
    If you are not taking the boat to the lower 48 you do not have to worry about ethanol as we do not have that up here.
    Ya I knew that of course...

  12. #12

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    Well changing the line from tank to motor did nothing+ a new bulb. It ran good for about 5 min, then same symptoms. Same thing, the fuel canister under the hood is mt, and after I pump it up I can cruise for a couple hundred yards. Ordered a fuel pump as the canister being mt makes me think it isn't obviously getting enough fuel. Pumping the bulb while running seemed to help a little...why can't toys just always run like they are supposed to. This crap has got me worried as I can't get to my moose area w/o this lil booger

  13. #13
    Member Frostbitten's Avatar
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    Quote Originally Posted by hunt/trapak88 View Post
    Well changing the line from tank to motor did nothing+ a new bulb. It ran good for about 5 min, then same symptoms. Same thing, the fuel canister under the hood is mt, and after I pump it up I can cruise for a couple hundred yards. Ordered a fuel pump as the canister being mt makes me think it isn't obviously getting enough fuel. Pumping the bulb while running seemed to help a little...why can't toys just always run like they are supposed to. This crap has got me worried as I can't get to my moose area w/o this lil booger
    Does your fuel line have the standard Merc quick connect fittings at the fuel tank and/or motor? There are o-rings in those things that have a tendency to wear out over time and allow air into the line which could explain what's going on. Been there before.

  14. #14
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    Do you have a timing light......... if so check each one of the coils to see if one of them is not firing. A scope would be better but I don't think you have one of them.

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    You seem like a smart guy, so I'm sure you already checked this, but I'll mention it for the sake of simplicity

    Have you checked to make sure the gas can is venting properly? Ask me how I know this...ha ha

  16. #16

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    Quote Originally Posted by dkwarthog View Post
    You seem like a smart guy, so I'm sure you already checked this, but I'll mention it for the sake of simplicity

    Have you checked to make sure the gas can is venting properly? Ask me how I know this...ha ha
    Not as smart as the dang motor. My cap does not have a vent on it, so I've been backing it off leavin it just tight enough to where the fuel won't spill out the cap. Today I had it backed off and just sitting on top.

  17. #17

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    Quote Originally Posted by Frostbitten View Post
    Does your fuel line have the standard Merc quick connect fittings at the fuel tank and/or motor? There are o-rings in those things that have a tendency to wear out over time and allow air into the line which could explain what's going on. Been there before.
    I put a new fittin on the tank and the hose goin to tank before my test today. The fittin on hose goin to motor is the 'spendy' one..I got tired of the 'cheapys' after disconnecting them just a few times the o ring would be shot. What really has me puzzled is that it will randomly run for 30 + mins fine. Like the other day I ran wot for 30 and ran fine. It does make sense that it would be the pump sice my canister goes mt after running for a few mins correct...??

  18. #18

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    I do not have the timing light to check the coils, but will go get what I need while I'm waiting on fuel
    pump. So what is this vst I've been reading about? Is it just a pump the low psi fuel pump feeds then feeds the injectors? I'm grasping at straws here. Kinda wanna take it to a shop as I go to work on Friday and will need it when I return from work..

  19. #19
    Member Frostbitten's Avatar
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    Quote Originally Posted by hunt/trapak88 View Post
    I put a new fittin on the tank and the hose goin to tank before my test today. The fittin on hose goin to motor is the 'spendy' one..I got tired of the 'cheapys' after disconnecting them just a few times the o ring would be shot. What really has me puzzled is that it will randomly run for 30 + mins fine. Like the other day I ran wot for 30 and ran fine. It does make sense that it would be the pump sice my canister goes mt after running for a few mins correct...??
    I agree, you've already ruled out some of the easiest to fix stuff. Unless there is a problem with the fuel pick-up tube in your tank, I'd be looking at the fuel pump.

  20. #20

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    Quote Originally Posted by Frostbitten View Post
    I agree, you've already ruled out some of the easiest to fix stuff. Unless there is a problem with the fuel pick-up tube in your tank, I'd be looking at the fuel pump.
    Took the pick up out and the screen was free, and could blow through it.

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