Mercury idle spark timing too high?

Discussion in 'Outboard Maintenance' started by Dillusion, Dec 12, 2012.

  1. Dillusion

    Dillusion devilray snob

    How important is having the correct spark timing on an outboard?

    My Merc 25 2-stroke with mechanical spark adjustment should be set to the 25 notch at 3500rpm and the 6 notch at idle. But currently- my idle spark at at notch 11.

    I hooked up a timing light to the motor and got that result. Adjusting the idle spark screw does nothing. 'Advancing' it by screwing in only raised it a few notches before not doing anything, and 'retarding' it by unscrewing the screw does absolutely nothing to the point where I can unscrew it to where it's not even touching the idle spark arm anymore.

    My carb is tuned correctly as per factory settings (1.25-1.75 turns out on air/fuel mixture screw) and idle screw is 'just touching' the idle plate with one additional turn in.

    My throttle linkages are also properly adjusted at 5.5 and 5.25 inches.

    The other linkage connecting to the spark arm is the timing link, which is NOT adjustable.

    Schematic for reference:

    The engine is currently running just fine at these stock settings, idling around 800rpm and fast idling around 1500 rpm.

    When I turn the throttle from 'start' into FWD or RVRSE the gears to do 'slam' and there is a smooth transition with just a nice light click when the gears engage.

    The only problem I can identify, is the little area where the idle spark adjustment screw contacts the idle spark arm is worn down and the plastic has an indentation in it.

    I ordered a new spark arm just in case.

    The engine works fine on the stand, but this issue is getting to me. Any additional ideas?

    I am using a cheap $35 timing these read badly like a cheap compression tester?
  2. cutrunner

    cutrunner Cert. Yamaha technician

    You need to be doing this under a load.

    Btw ive seen people use 35$ timing lights to tune 7 second cars just fine.

  3. Dillusion

    Dillusion devilray snob

    I was doing it with the LU submerged in a tank just as the manual says.
  4. HaMm3r

    HaMm3r Well-Known Member

    Sounds about like mine, although I've never put a timing light on it. In gear, I idle around 690 rpm and in neutral about 780 once the engine is warmed up. There's a light "thunk" when I put it in gear, but it's not enough for me to worry about.

    I'll be interested in the responses you get though.
  5. Dillusion

    Dillusion devilray snob

    It seems to be a trade off between the amount of times my idle RPM screw is turned and where my idle spark sits, but I can't get it to where it is 'as per the manual' at a spark of 6. Even if I screw the spark all the way out until it's not touching the spark arm, and turn in the idle speed screw 4-5 turnes, the spark is still at 11.

    Could be bad coils? powerpack? stator magnets? lol

    Not hearing a 'thunk' or 'grinding clunk' when changing into gear is a good thing, it means the gears arent smacking together and you arent at too high of an RPM.
  6. Creek Runner

    Creek Runner Well-Known Member


    ;DThis is funny, did your manual tell you that! Even though you were a smart --- to me, I'll help you out a little.

    No your coils, power pack, or stator isn't bad, and to answer your 1st questions it's very important to have the correct timing as incorrect timing can cause Pre-ignition and -detonation which both will cause a catastrophic internal failure .

    Now since you're so good at reading you should be able to figure it out with the manual.
  7. Dillusion

    Dillusion devilray snob

    I was being a smart ---, it was just the second time you quoted one of my posts after we decided my response was not the solution ;). I have thick skin so I didn't really care, I offered my rebuttle with a screenshot and a little spice :-*.

    I cannot fix it with just the manual. I have read it front to back and I cannot solve the issue. Thats why I'm asking.
  8. AfterHours2

    AfterHours2 Stripper in my own Mind!

    Somebody get this guy a new Shadowcast ASAP! I know how you feel man. You just want everything to par so when the boat arrives no time on the water is lost. Between Cut and Creek, they should get you straightened out. Best of luck....
  9. Brett

    Brett > PRO STAFF <

    Setting the timing is part of the Timing/Sychronizing/Adjusting procedures in the shop manual.
    After setting up the linkages per the manual, initial adjustment of the timing is completed using
    the trigger link rod. Have to snap one end of the link rod sockets off the ball mount, then turn
    the rod to lengthen or shorten overall length to obtain desired settings. Final timing settings
    are done with the maximum timing screw and idle timing screws.

    According to my manual, idle is 6° btdc and at 3500 rpm should be 25° btdc.

    Note: on the electronic spark advance models, at low rpms, idle may auto adjust to 11° btdc
  10. Dillusion

    Dillusion devilray snob

    Mine is a mechanical spark advance which has two screws, the directions you quoted above are for electronic spark models.

    The mechanical spark advance models do not have an adjustable trigger link rod, as shown in photo on 2C-8.

    I have two mechanical adjustment screws, one on the fuel pump and under under the flywheel.

    I have the manual and that wording is from section 2C...

    Problem is, I have done all that. My linkages are adjusted, my carb mixture screw is 1.5 out and my idle rpm screw is jus touching + 1 turn in.

    I'm assuming that the mechanical spark advance models will auto adjust to 11 as well? What's the point of the manual saying 6 degrees +-1 then?
  11. Brett

    Brett > PRO STAFF <

    Nope, only the electronic controlled auto advances.
    Sounds like one off the linkages/rods is slightly off.
    The timing/synchronization has to be completed exactly as per the manual.
    Not sure if you've got a worn nylon follower or connector that's allowing the change.

    plus or minus means "close enough for government work."
    It's not a race engine so a degree off doesn't hurt.
  12. Dillusion

    Dillusion devilray snob

    Here's a photo of what I'm talking about. Where the idle spark screw touches the spark arm, it's worn down allot in the plastic:

    Under the screw (you cant see well) it's so worn down it's alomost like it's chipped off.


    And heres a photo of both my spark screws for an idea of how they are currently set:

  13. Dillusion

    Dillusion devilray snob

    Manual states:

    Shift Link Rod -- Adjust to length of 5-1/2 in. (13.9 cm) - DONE
    Throttle Link Rod -- Adjust to length of 5-1/4 in. (13.3 cm) - DONE

    Problem still persists...
  14. Dillusion

    Dillusion devilray snob

    No, I have not touched that one. That is the maximum timing screw for when at 3500RPM or more...?
  15. Brett

    Brett > PRO STAFF <

    Not sure what you've got going on. Sounds like you've done things per the manual.
    Wondering about the what's taking place between the stator plate and the throttle linkages.
  16. Dillusion

    Dillusion devilray snob

    I have the engine running pretty smoothly... it speeds up and returns to idle without dieing. it will idle in a tank or on a hose for 15-25 minutes without dieing as well.

    This spark problem is just annoying me, because if my spark is high that means I have something else turned too low-

    I am experienced a 'clang' or 'knock' sound around my stator area with every revolution.

    Any idea? Related?
  17. Brett

    Brett > PRO STAFF <

    Clang or knock is not a sound I want to hear from an outboard.
    Something is out of position, possibly on the stator plate.
    If one of the components is making contact with the underside of the flywheel
    there's a good chance of breakage occurring, leading to a short in the electrical system.
  18. Dillusion

    Dillusion devilray snob

    Sorry it's not on every revolution, it's more of a 'click' sound and it's once every few seconds.

    So I guess the flywheel cover is coming off tonight...

    EDIT: On page 2A-7 of the manual,it states this:

    The spark timing is changed (advanced/retarded) by rotating the trigger coil, which
    changes the trigger coil position in relation to the magnets in the center hub of the flywheel.

    Could something be loose/off in the stator area?
  19. Swamp

    Swamp I Love!

    Different engine, but I had a charging coil screw back out on a 25 Johnson.  In hind site it had been "hitting" for a while.  It finally "caught" while it was at idle and I was getting rid of some "personal bilge water".  Rotated the ignition plate 90* and chewed up the fly wheel some.  While fixable (lucky), I was done for the day.  I was in Coot Bay and it was a long tow back in.  Stupid on my part.  So yes, something can be "off" I'd yank that fly wheel immediately if for nothing but having peace of mind.
  20. Dillusion

    Dillusion devilray snob

    Ok, I will definately check for that also.

    Since the timing coil can affect the spark timing, I'm thinking the previous owner didnt install it correctly and it's in a position where the mechanical idle spark timing screw somehow does nothing to change it.

    Last night I messed with it some more, and it seems that backing out the idle screw to retard timing does NOT retard the timings, only makes the engine RPM lower and die out.