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  1. #1
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    2.5 260 EFI - Stalls a lot when you put in gear

    Hi guys. Just picked up my first STV with a 2.5 260 EFI ss. 2.5 runs strong when I hit open water, awesome throttle response. My issue is getting to open water. There is a narrow bay and a series of channels I need to go through to get to open water. The 2.5 doesn't like waiting for open water. It stalls all the time going in and out of gear and running at slow speeds through the channel. Makes trying to maneuver in the tight bays a massive pain in the ass. It idles smooth in neutral without any issues. It has offshore mid and I run a 30 lightning on it. If I trim way up to keep exhaust above water it is a bit better but still stalls out a lot.

    Any thoughts? - If this normal for 2.5 and I just need to learn how to drive it that is good to know too haha

  2. #2
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    You seeing a lot of blue smoke? Maybe a little too much oil? How about a fresh set of plugs? The hi-po engines are not designed to idle for long periods of time. They are fuel and oil rich and have to be that way.

  3. #3
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    It could be too much oil, it was smoking a lot. i mixed at 30:1, i thought a little more oil was better than not enough. I can try a leaner mixture on the next tank. Plugs are new, only a couple of hours on them.

  4. #4
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    Always mix the ratio accurately. The proper ratio is 40:1 I believe. Check your owners manual to be sure. Setting it up for shifting in gear is a good way to avoid stress on the gearcase. Might help with the stalling out problem also.

  5. #5
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    No manual, just google. i saw posts for anything from 24:1 up to 40:1. Had this fear of blowing it up on my first run so started at 30:1 ahaha. I will mix next tank 40:1 and try it again. Yah, it will start in gear and I was doing that. Thanks for help btw

  6. #6
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    I just looked it up and from what I saw a 32:1 mix is correct.....So, just needs a lot of oil. And won't like to idle....

  7. #7
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    You need to clean the map sensor fitting on the horn.the one that the ecu Vacum hose connects to.should help your cause.

  8. #8
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    Could raise idle rpm to 1200 helps on mine in long idle situations most of the time I foot throttle to 1500 to keep them from slobbering poor bastard behind me

  9. #9
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    .. Get a New @ least Group 27 Battery. That Solve Your Problem

  10. #10
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    That barb on the horn feeding air signal to ECU being clogged has made many people pull their hair out , I use a propane torch after tygon removal soon as it gets heated blow through the barb with compressed air ... it could be your issue , it has a very fine air way and clogs frequently ...BTW 32:1 is the correct oil - fuel ratio
    Last edited by Jay Smith; 05-19-2019 at 06:58 PM.
    Jay @ JSRE

  11. #11
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    260 is as 260 does. With a stock ecu they weren't the most tractable motor without fine tuning.

  12. #12
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    Clean the barb on the horn.

    Check the rectifier.

    Adjust throttle opening and advance.

    I used to be able to idle a 260 in gear at 600-700 rpm.
    Markus' Performance Boating Links:
    www.toastedmarshmallow.com/performance

  13. #13
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    had same problem on my 260.
    check the barb as said before but if that doesn't fix it, it's your ecu.
    i went crazy trying to figure mine out. swapped several used ecus with about same result. seems the old merc ecus go rich at idle when they age. several times i had to disconnect the fuel pump just to get it started.
    changed to an ACU and the thing idled like a 4 stroke and no rich smoke. it lost a little on top end but it was worth it on a fishing boat.

  14. #14
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    Thanks for all the suggestions guys. Going to dig into it this week and hopefully have it straightened out for weekend.

  15. #15
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    You should be able to find instructions if you use the search functions.

    From what I remember, you close the butterfly, set advance to what the manual says, and adjust advance from there. From what I remember, the sensitive place is where the butterfly starts to open.
    Markus' Performance Boating Links:
    www.toastedmarshmallow.com/performance

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