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  1. #1

    Question Mercury 90hp inline 6, carbs rebuilt - still no power under load

    Serial OA969038

    Engine has been in storage a long time, just bought it used a couple months ago.

    I've replaced the water pump impeller, rebuilt the fuel pump, replaced all fuel lines and filter, rebuilt all three carbs - including new jets, new floats, new needle/seats, and replaced the plugs with NGKs
    (same number as the ones that were in it when I got it - which still had the black paint overspray on them from the factory)

    The engine starts easy and runs well in neutral, not velvet smooth at all rpms, but I've not even adjusted the idle needles yet (2 turns out from bottom to start).

    In gear - it bogs, stumbles, surges, and just won't GO, it won't stall, but it just won't accelerate.

    I have a feeling it's ignition system related - but I'm not sure how to diagnose it. Plugs have been replaced more than once before rebuilding the carbs (found one cracked float and had some debris behind the seat on one carb)

    Overall the engine looks new under the cowling, wiring is in good shape, no burn marks evident in the coil packs, etc. Spark plug wires are in excellent shape.

    If this was a car (which I'm much more familiar with) - I'd be thinking the mechanical advance mechanism inside the distributor was stuck, keeping the advance at the idle spec....

    Pleas enlighten this car guy on the ways of the merc tower of power 2 stroke outboard ignition advance system!

  2. #2
    Join Date
    Nov 2001
    Location
    South Carolina
    Posts
    2,595
    You may have a bad high speed side of your stator.
    Put the boat in the water on the trailer.Hook up a timing light to #1 cyl. Start the engine and let it warm up. Shift into forward, prop on, and slowly give it throttle. Watch the timing light to see if the flashes get erratic.
    It would appear the stator may be bad.
    Also remove the air jets in the top of the float bowl covers and throw them away, leave the hole open. Let us know what happens.
    Don't try this on a hose, and you don't have to take the boat off the trailer.
    Never argue with an idiot. They drag you down to their level, then beat you with experience.

    3 X APBA Formula V Nat'l Champion
    APBA Formula V US-1
    It took me 29 years to become an overnight success.

  3. #3
    I'll give that a shot - it's on a pontoon that stays in the water on mooring whips...
    I'll have a friend help me to operate the boat while I operate the timing light.

    hm - stator - that sounds expensive and hard to fix... pull the flywheel first right?

  4. #4
    Join Date
    Nov 2001
    Location
    South Carolina
    Posts
    2,595
    Easy if you have a flywheel puller.
    Never argue with an idiot. They drag you down to their level, then beat you with experience.

    3 X APBA Formula V Nat'l Champion
    APBA Formula V US-1
    It took me 29 years to become an overnight success.

  5. #5
    who's got one I can rent?

  6. #6
    My guess is that your are too rich to start out with. If my memory is right, the low speed settings to start with is one turn out, not two.
    194264

    1988 concord magnum 22 200 hp black max
    16' marlin 135hp johnson v4
    tow vehicle 2001 dodge durrango r/t 360 magnum

  7. #7
    I thought I was following the advice of this board I got before I rebuilt the carbs a few weeks back - the idle is just fine - I will re set the mixture screws after removing the air bleed jets as suggested above..... but - that's not what's making it not pull a load worth a darn.....

  8. #8
    Join Date
    Aug 2002
    Location
    Sacandaga Lake!
    Posts
    1,013
    Quote Originally Posted by milner351 View Post
    I thought I was following the advice of this board I got before I rebuilt the carbs a few weeks back - the idle is just fine - I will re set the mixture screws after removing the air bleed jets as suggested above..... but - that's not what's making it not pull a load worth a darn.....
    The light idea sounds great to me and an easy way to tell how things are firing. As far as carb adjustment it is pretty critical on these. 2 turns out was a great start for mine. They were at 1 turn and it wouldn't plane. At 1.5 it wouldn't and 1.75 it seems to be just right on mine.

    The timing is also critical. Doing it on the lake was important on mine too. A spark tester or 6 of them is also good to have. They sound pretty good on 5 cylinders idling but won't plane too. I had the wire from the coil to the swithbox go bad on #2 last week. I wouldn't have found it without the spark testers. They are cheap too.

  9. #9
    Spark testers I have - well, not 6 of them but - one or two.

    Another question I want to confirm with you who know --- firing order?
    I want to make sure the wires are all on right... .oh boy would I feel foolish if it's just a mismatched spark plug wire!

  10. #10
    Join Date
    Jul 2005
    Location
    Regina SK. Canada
    Posts
    496

    Firing order

    Should be imprinted on the water jacket beside the plugs.Glen

  11. #11
    Join Date
    Mar 2005
    Location
    Chestertown, NY
    Posts
    285
    wouldn't rule out the stator. get ur hands on a peak reading voltmeter. classic mercury tune-up.

  12. #12
    Join Date
    Aug 2002
    Location
    Sacandaga Lake!
    Posts
    1,013
    Quote Originally Posted by matty b View Post
    wouldn't rule out the stator. get ur hands on a peak reading voltmeter. classic mercury tune-up.
    I agree. Before taking anything apart do the easy tests. Like Jeff G said the timing light won't give a steady flash with an electrical problem. I haven't used the voltmeter method but I imagine that is good too. How do you hook that up to see if it is dropping under a load?
    Last edited by BigJohnson; 08-27-2009 at 06:56 AM.

  13. #13
    I will do the timing light test before I take anything apart.
    I'm assuming I can put the timing light on each spark plug wire as a test to see if all of the coil packs are working properly as well?

    Overall - everything under the cowling of this engine looks new - but - it is hard to see under the flywheel to inspect the stator.

    I will hunt on ebay for a flywheel puller.

    Do these inline 6 mercs have 1 1/2"-16 threads?

    http://cgi.ebay.com/ebaymotors/Flywh...=p4506.c0.m245
    Last edited by milner351; 08-27-2009 at 10:09 AM.

  14. #14
    Join Date
    Mar 2005
    Location
    Chestertown, NY
    Posts
    285
    Quote Originally Posted by BigJohnson View Post
    I agree. Before taking anything apart do the easy tests. Like Jeff G said the timing light won't give a steady flash with an electrical problem. I haven't used the voltmeter method but I imagine that is good too. How do you hook that up to see if it is dropping under a load?
    same as checking spark- hooked up on the trailer. i think there is a red and a blue wire coming from the stator. red is high speed and blue is low speed. not positive, but i think you are looking for around 200 volts.

  15. #15
    Sorry to let this hang out there so long. Been busy with a million other things.

    I swapped the stator out this year - and, after following the genuine merc service manual instructions for synchronizing the ignition / carbs - TWICE.........

    IT RUNS GREAT!

    Thanks so much for all the help. I got a flywheel puller from ebay which also came with a lifting ring. I used that to lift the engine up from the lowest mounting position (new b error on my part when initially putting the engine on the new transom) to the highest mounting point.

    At the lowest height, it plowed a ton of water - I still have the fuel tank and battery mounted to the top of the back of the pontoons - and everything was getting showered with spray - not good - so - with a chain hoist and the boathouse frame work - I got it moved to the highest mounting position on the transom and gave that a try...... cavitation at anything past 1/2 throttle.

    After looking at many other 'toons on our lake - I noticed most of them had the engine tilted quite a bit to create a more "bow down" tilt under power.
    So - I moved my lock pin on the transom mount forward a few holes and gave it a try - SUCCESS!

    WE HAVE WOT!

    now - to swap on the prop I got which several online calculators indicated would be appropriate for this 90hp inline mounted to a somewhat inappropriate barge - our '78 crest 25ft pontoon boat. It's a 14x13 3 blade - I'm not sure what 3 blade is on it now - but the PO of the outboard indicated it was on a small speed boat - so - likely a mismatch.



    NEW QUESTION:

    This is a manual tilt engine set up - no hydraulics. I can't get the transom reverse lock to unlock!!!

    I want to be able to tilt the lower unit up and out of the water when not in use.... currently - I can't figure out any way to get the lock to unlock and allow me to tilt the engine.

    Ideas?
    Last edited by milner351; 08-03-2010 at 10:37 AM.

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