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1982 tower of power timing questions

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  • 1982 tower of power timing questions

    Hey guys. I grabbed an old rotted cobra ski boat with a 115 merc on it last summer. long story short I used the boat once and then picked up a 92 Larson senza with a 70hp force on it. I ended up selling the force and swapped the merc onto the senza. When I first got the merc it hadn't been ran In a few years but got it to start fairly easy once i got it primed. It runs fairly well but I think it needs a bit of tuning. according to the previous owner the boat had sank at one point in its life and the motor had been rebuilt.

    Anyways before taking it out for the first time last weekend I put the motor on some muffs and dialed in the throttle/shift cables. when I was doing that I noticed the carbs weren't fully opening, and it was idling a bit higher then ideal (no tach). I adjusted the stop screws on the big shift arm on the side of the motor to fully open the carb and to lower the idle. From reading online about timing I think I may have lowered my static timing and advanced my dynamic by doing this? either way the boat ran pretty well it started and idled fairly easily. it feels a bit sluggish and I just don't think im getting everything out of it that I should. Hole shot in particular is pretty weak and it struggles to get up on a plane. top speed was about 42mph by myself and 36mph with some friends in a 17' 1300ish lbs boat on a tidal river with decent current.

    Now Ive read through this https://forums.iboats.com/forum/engi...-1988?t=168855 and ive watched some videos but most of what I find seems to be geared more towards the older motors with distributors. Before I start messing with all of this I just wanted some confirmation on if I have the right idea or not. I'm new to boats but not new to engines or mechanical work. the guide lists the throttle lever hitting a cam to engage the dynamic timing. I assume this is for the distributor models? I believe my timing is advanced by the cam in the middle of the big throttle linkage on the side of the motor and is internal?

    this is my understanding of the procedure:

    1. finding tdc for cylinder 1 is basically to just confirm the timing marks are where they should be and the flywheel (or whatever it is called) is in its proper orientation? if its not I would need to mark the flywheel or the housing adjacent to the sticker at 0 degrees with the piston at tdc?
    2.
    remove throttle cable and put linkage

    set throttle to idle turn throttle screws on carbs to fully closed (lightly seated) then set them 1-3/4 turns out
    3. pull spark plugs and in idle position and crank motor with timing light and aim for 3-4 degrees by adjusting the stop screw
    4. move linkage to full throttle position and crank motor and adjust stop screw to 20-21 degrees
    5. adjust the carburetor throttle linkage to allow full throttle movement with timing linkage

    Are the next 2 steps talking about the idle fuel mixture screw or is there a physical stop screw on the carbs?
    6. start the motor with the leg in water and warm it up to operating temp fine tune the idle to 800rpm, then slowly close the idle stop screw on the each carb until it starts to stumble then back out 1/2 turn
    7. put motor in gear and lower idle to 500-600rpm then readjust each carbs throttle stop screw until it stumbles and then back out 3/4 turn? is there a separate idle screw for in gear idle speed or how is that different then the last step? is it just the load on the motor that lowers the idle speed and you are just tuning it for that making the last step kinda pointless?

    Other then that when I was using the boat half way through the day it started constantly loosing prime. whenever I would turn it off id have to pump the ball to get it going again, and sometimes it would die after 30 seconds or so and need to be pumped a few times until the motor would stay running. Im also leaking fuel from one or more of the carbs. I think this is a sign of worn out floats and ill need to rebuild the carbs?

    can anyone just confirm my timing specs and that everything is proper before I start ripping into it? once I have the motor running half decent im going to look into changing out the prop. I have a portable tach showing up this weekend which will help give me an idea of where im sitting at. whats my ideal rpm with this? like 5500 at wot and 1 person in the boat?

    I also read something about the 90,115,125 and 150 all use the same motor? can you swap carbs or something to turn a 115 into a 150?
    Last edited by Mybiggles; May 17th, 2019, 08:42 PM.

  • #2
    The 90, 115, 125, 135, and 140 share the same Bore and Stroke, and therefore the same displacement. They are not the same, there are many difference between these engines and swapping carbs will not make a lower HP model into a Higher HP model.

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    • #3
      Timing on these motors rarely needs attention.----It is fixed at the factory for the life of the motor.-----Careful if you decide to adjust anything !!

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      • #4
        You can easily check timing. Remove spark plugs 2-6 and install them into their wires and ground them. Push the throttle open until the carbs are about to open, but still closed. Put a timing light on #1 cylinder and crank motor. Idle pickup timing should be between 0 and 9* ATDC.


        Now advance throttle fully and crank motor. Max spark advance should be 21* BTDC.

        If you need to adjust it, I would invest in a service manual. All timing and idle speed and throttle stop adjustments are on the throttle arm.

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        • #5
          Originally posted by Chris1956 View Post
          You can easily check timing. Remove spark plugs 2-6 and install them into their wires and ground them. Push the throttle open until the carbs are about to open, but still closed. Put a timing light on #1 cylinder and crank motor. Idle pickup timing should be between 0 and 9* ATDC.


          Now advance throttle fully and crank motor. Max spark advance should be 21* BTDC.

          If you need to adjust it, I would invest in a service manual. All timing and idle speed and throttle stop adjustments are on the throttle arm.
          a service manual is a good idea but im not sure where I can find one locally. im gonna try and have a go at it today. ive been reading a lot online, I just wish I could find more information on what screws do what. my understanding is the 2 adjustment screws on the big throttle arm are the low and high speed timing adjustments? ive kind of read conflicting information about the idle speed adjustment. some things say its only set by the idle timing adjustment and other things talk about an adjustment on the carbs throttle arms?

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          • #6
            On two stroke outboards the idle speed is set by retardation of the spark. The carbs are closed, or they should be. They will remain closed for quite a bit of the initial throttle linkage movement. At a specific timing point(primary pickup) the carbs will open slightly, and after the timing is fully advanced, they will open fully. The lower screw on the big throttle arm is the idle speed stop screw. The upper screw is to stop linkage travel once the carbs are fully open, to keep the carbs from being pushed past fully open, or damage to the linkages by more pressure from the control box. Max Timing is set on by a screw on the linkage nearby the Pickup Timing Screw. The only adjustments on the carb(s) regarding low speed are the idle mixture needle. Adjustment of them can affect idle speed, which then needs to be reset. Adjustment of the idle speed requires the Throttle cable be free, as the required preload on it will need adjusting once the idle speed is adjusted. Too little preload and idle speed will be inconsistent, too much and the control box gets difficult to shift in and out of gear.
            As mentioned a Service Manual, preferable a factory one, for your engine will lay out the exact procedure for checking/adjusting your engine. Generic Manuals can often be found at Public Libraries, some are poor to fair, others aren't even good for lining bird cages.
            As racer said, the settings shouldn't need adjusting for the life of the engine. They need checking when the carbs are removed and replaced, and adjustments are rarely if ever needed. My 1984 115 wasn't touched for over 15 yrs
            Last edited by jimmbo; May 18th, 2019, 10:44 AM.

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            • #7
              I lifted the motor almost 3" so the anti aeration plate is about 1.5" above the bottom of the hull (was about 1.5" below before). the motor is also on a cmc hydraulic trim mount which pushes it 6" off the transom. I brought the boat on the river again today and top speed was about the same. it did however get on plane much easier then it did before. I think the motor is a bit high now as trimming up, or cornering causes ventilation. I'll have to redrill my mounting plate, but im gonna try and lower it about .5-.75" which should be about perfect

              when I adjusted the throttle the other day I guess I just opened up the throttle stop to allow the carbs to fully open which was what I thought I was doing at the time. When I lowered the idle I did so with the idle speed stop screw. I eventually thought (wrongly) these screws were what controlled idle and max timing points. So if you are saying at idle the throttles should be closed and its only adjusted by the base timing spec, shouldn't loosening the idle speed stop screw not affect idle speed then? would this not be an indication that my base timing is set incorrectly? if I back the idle speed stop screw all the way out the motor will drop so low it will die, which from my understanding means its base timing is too low?

              I looked at the throttles and linkages and everything today and I think I wrapped my head around everything. above the carbs on like the top corner of the motor there is a max and minimum screw and then there is like a shaft that goes towards the rear of the motor. these are the timing adjustment screws correct?

              I know timing is a set and forget kinda thing but the previous owner told me the boat had sank at one point in its life and the motor had been rebuilt. based on the throttle stop screw being incorrectly set im kind of thinking the timing may have been set incorrectly as well, or at the very least is worth taking a look at to confirm its correct.

              beyond that my carbs are leaking gasoline pretty badly. Does anyone know part numbers for wmk 28 carb rebuild kits?

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              • #8
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                There is no Base Timing. There is a Max Timing and a Pick up(where the carbs are just about to open a wee bit) timing spec. Retarding the timing to whatever it needs to be, is what sets the idle speed. There is no set spec for timing at idle and it will vary depending on the load.

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