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1981 70 hp timing issues

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  • 1981 70 hp timing issues

    Finally got her out on the water and timmed it. Acted kinda funny, but basically to bore the long story.... first Just a quick view on how engine ran before, Motors never ran bad. Does seem like low end torque is low under 3000 rmps but thought that was normal. Timimg advance is 19 degrees. Timing initially read at 12 degrees. Bump it up 3. Ran at 15 degrees. Bumped it up 2 more turned, stayed the same. Bumped it up one turn, now reading just under 16. Maybe 15.75 degrees.

    Off my first reading, the timimg should be 18 if one turn consistantly equals on degrees. But its reading just under 16 and hadn't really changed much after 3 turns... not really sure what's going on.. maybe some water got on coils and cause it to do that?... is it a part that's going bad...?

    Going to try the jim Reeves method and see that reading I get. Somethings not adding up. Had good compression when checked 2 years ago.. could check it again, not sure if that would make a difference. Following as the OMC manual says besides using a test prop..

    Did it run better, maybe... hard to say. It did plane very fast and at full cruise within 7 seconds. Prob on Plane in 5 or less. So maybe improvement, but i also linked and sync. 1900 to 2000lb loaded boat with 17 stainless prop.

  • #2
    Your #s make no sense at all. I ran that motor on a 16' boat and a 15" pitch was a good all around prop. A 17 was for lighter loads. With a 17" pitch on a 650# boat that motor it 5-5200 rpm. A 1900-2000# boat would be a struggle for that motor with that prop.

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    • #3
      Originally posted by flyingscott View Post
      Your #s make no sense at all. I ran that motor on a 16' boat and a 15" pitch was a good all around prop. A 17 was for lighter loads. With a 17" pitch on a 650# boat that motor it 5-5200 rpm. A 1900-2000# boat would be a struggle for that motor with that prop.
      Well it's a stainless 17 not sure how that effects it. Boat is 800 to 900 lbs dry. Plus 400lb(2 persons) fuel is about 100 lbs. Batteries 180lbs plus tackle, seats anchor and kicker motor. Maybe couple hundred. Hard to say. Over 1700lbs for sure

      Rpms at 5400. Is a trihaul

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      • #4
        You have to be very careful if you start adjusting the timing on these motors.-----Basically you set maximum advance.----Idle timing looks after itself.------Idle ---" pick-up " timing is where throttle plates open.-----Maximum timing advance is set at the factory and rarely needs adjustment !!!

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        • #5
          Opps, I forgot the weight of the outboard. Which is 2-230 lbs. So I believe my original estimation is about right

          Boat is a 17 foot fiberglass tri haul with 80 inch beam

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          • #6
            Originally posted by racerone View Post
            You have to be very careful if you start adjusting the timing on these motors.-----Basically you set maximum advance.----Idle timing looks after itself.------Idle ---" pick-up " timing is where throttle plates open.-----Maximum timing advance is set at the factory and rarely needs adjustment !!!
            The person that had this before me deffinetly had his fingers it it. Stuffs been all over that wasnt right. Regardless I was trying to get wot timing as the manual said, but without a test prop. I understand how the theory works well. Didnt try to keep cranking it up for that very reason.

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            • #7
              Doing alot of forum searching, I found that sometimes some timimg lights dont work well.. I was using a digital snap on light with tach. Maybe that caused some problems with it being an oddball. In a post someone mentions a snap on light and it jumping around for some reason.. idk. Just tryna think of everything

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              • #8
                Any timing light will work. The problem people have is they let the pick-up drop and it picks up the cylinder under it. I would double check.your tach.

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                • #9
                  Originally posted by flyingscott View Post
                  Any timing light will work. The problem people have is they let the pick-up drop and it picks up the cylinder under it. I would double check.your tach.
                  Hmm. I'll have to do that. I had it right at idle via multitool. Maybe it changes at wide open..

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                  • #10
                    Checked tach and is working correctly.

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                    • #11
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                      Did a compression test just to check. Start at cly. 1 reads 142 139 140. Anyone know what the issue might be? Thanks

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