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1991 OMC timing scale/general help needed

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  • 1991 OMC timing scale/general help needed

    Hello Everyone,

    I have a 1992 Sunbird Corsair 175 with a 3.0L OMC (GM I4) engine that I'm having some issues with.

    First a little background may be necessary. The boat has been sitting for the past 5-6 years, and required what would be typical of something that has been treated in a similar way. It was winterized, but not very effectively from what I've gathered.

    Here's what I've done so far, and why:

    Replaced Spark Plugs and all fluids - General tune-up

    Replaced Distributor, rotor, ignition module - Engine would crank/spark but not turn-over.

    Replaced Starter - Father-in-law burned it up.

    Replaced Impeller - General necessary maintenance.

    Replaced the carburetor with a Holley 500CFM 2BBL Marine Avenger - Engine would not run properly/at all.

    After doing all of this, and ensuring the carb was adjusted to the original specifications, the engine finally began running well enough for me to believe it was ready for a lake test. I was wrong.

    Once we got the boat in the water and got it started, it would backfire and stall as I gave it throttle to try and keep it running, unless I was able to immediately retard the throttle before the engine stalled out. If I did not give it some gas, it would die. If I gave it gas, it would backfire. A couple of times it would also spew gas out of the top of carburetor upon dying.

    Oddly enough, the engine seemed to stabilize to the point at which I was able to putt around in it a little bit, but when attempting to advance the throttle to full, the engine would either stall out at WOT, or it would not accelerate beyond a certain point well beneath WOT even though the throttle was placed there. For some reason it's only advancing to a certain point and then ceases to perform further...eventually, the engine died and so did the battery, and I wound up having to flag down another boat for a tow.

    Will this in mind, I figured the first step I would take due to the inconsistently consistent backfiring would be to ensure the engine is properly timed. Which leads me to my current problem. The Timing Scale on the engine is corroded to the point that the degrees/markings are no longer visible at all. They're completely gone.

    So, my question is, is there someone out there that has this engine that could snap a picture of the timing scale on their engine, or is there somewhere I could get a replacement scale so I can ensure the timing is accurate? I've tried googling to see if I could find a picture of the scale, but haven't had much luck finding anything that matched my engine exactly.

    I appreciate any help that you all can offer, and please be sure to let me know if I'm misguided in going after the timing first, or at any point in what i've done. I'm an aircraft engine mechanic by trade with little experience on boat engines, so I'm open to any and all suggestions of those more experienced than myself with these things.


  • #2
    start at the fuel tank and clean it after sitting, the inside of the tank will need to be cleaned

    timing is 6 BTDC

    the big notch valley is 0 degrees
    the first peak is 4 degrees, the valley is 6 degrees, the second peak is 8 degrees, the second valley is 10 degrees and the third peak is 12 degrees

    so align the line on the damper to the fist valley above the big notch
    Cheesehead boating the Gulf Coast of FLA 27.51° N, 82.53° W

    1988 Cruisers Rogue 2420 -VP 290 DP now powered by custom 468 - https://forums.iboats.com/forum/owner...988-rogue-2420

    Past Boats
    1970 Wooster Hellion - Merc 9.8
    2002 SeaRay 190BR - 5.0 - A1G2 - "Cheeseheads in Paradise"
    1984 Avanti 170DLI -3.0 stringer- "Ship Happens"

    What’s behind you doesn’t matter.Enzo Ferrari


    • #3

      Thanks for your reply!

      I'll give the fuel tank a good cleaning. It was emptied out before it was put up but I'm sure there's plenty of residual scum.

      The timing scale does not have notches of varying size. I'll upload a picture of it whenever I get a chance, and perhaps that will help clarify.

      Also, I do have the manual for the engine which states BTDC is supposed to be at 0. My main problem is having no reference markings for getting it timed.


      • #4
        Timing tape works well too for badly corroded timing marks, of course you have to find TDC first before placing down the tape . But I am willing to bet some good old eblow grease and sandpaper would clean up the marks nice and shiny.
        1977 Bellboy 18 footer / 175 HP OMC 302 / 83 Mechanical outdrive

        "The trouble with quotes on the internet is that it's difficult to determine whether or not they are genuine." - Abraham Lincoln


        • #5
          This is what I'm working with. Elbow grease is just going to disintegrate what's left I think.


          • #6
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            yup , that is pretty hammered .

            I thought you were talking about the scale on the harmonic balancer .
            1977 Bellboy 18 footer / 175 HP OMC 302 / 83 Mechanical outdrive

            "The trouble with quotes on the internet is that it's difficult to determine whether or not they are genuine." - Abraham Lincoln