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dwell verses feeler guage merc 140 hp

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  • dwell verses feeler guage merc 140 hp

    Hi all,

    First of all I'm dealing with a 1986 mercruiser 3.0 140 hp. Alpha one gen one. Delco distributor.

    I just got done installing new points, condenser, cap wires etc.

    I set the points to .022 as per manual.

    I then set the dwell at around 32 deg. as per manual. (28-34)

    I noticed when I set the dwell I really opened the points up alot. I didn't recheck the gap but was wondering if this is OK?

    My gut says yes but it just seems odd.

    My boat seems to have a slight miss at WOT.

    I was playing with the timing and the idle speed on the lake today until the starter went kaput. So tommorrow a new starter will be here and installed.

    It seemed to run good but the starter was dragging so I retarded the timing to get back to shore, that's when the starter took a dump. (it's been dragging a little for a while but I thought maybe battery issues)

    I removed the starter and bench tested, it is hit and miss so I ordered a new one.

    My thought is maybe because the gap is so wide the points are "floating" at higher rpms. Wide open is reading about 4200 on the boats tach.

    DougV>


  • #2
    Re: dwell verses feeler guage merc 140 hp

    im sure others will jump in, but i feel the dwell reading is far more accurate than feeler guages. I would use feeler guages to get close or in a pinch but always prefer to stick a dwell meter on it.

    Id check the wires and plugs for your miss at WOT.

    Condensers can do funny things too.....

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    • #3
      Re: dwell verses feeler guage merc 140 hp

      A dwell meter is definitely the better way to go. Last year, I swapped the original, believe it or not, points in my 1985 3.0. It took me many attempts at using a feeler gauge to get the boat to run "just right."

      Comment



      • #4
        Re: dwell verses feeler guage merc 140 hp

        Thaks for the quick reply MBaker,

        New wires and pugs with the tuneup. (not to say that couldn't be the problem)

        I also replaced the old prestolite distributor with a "new" (to me) delco. The bushings are tight and the advance weights/springs are free.


        DougV>

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        • #5
          Re: dwell verses feeler guage merc 140 hp

          don't forget to set the timing again after ya adj. the points. dwell effects timing.....
          'Lime Time'
          1975 AristoCraft Nineteen
          Mercruiser 165hp (chevy 250 L6), MC-1 drive

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          • #6
            Re: dwell verses feeler guage merc 140 hp

            I set the gap (on the bench before installing new/used distributor)

            Installed and "clocked" distributor.

            Lastly, timed and reset idle speed. (idle speed has needed attention for a while now)

            DougV>

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            • #7
              Re: dwell verses feeler guage merc 140 hp

              Originally posted by djvan View Post

              Lastly, timed and reset idle speed. (idle speed has needed attention for a while now)

              DougV>

              If you mean that you set the idle speed and THEN set the time... then that's correct. If you really did set the timing and THEN the idle speed... then that's not correct. You need to have the dwell correct and the idle speed correct, then the timing.

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              • #8
                Re: dwell verses feeler guage merc 140 hp

                Maybe my dwell meter is junk. Haven't used it in so long I had to blow the cobwebs out of it.

                I set the gap, then the dwell, then the idle speed, then the timing.

                But I had to re set the idle speed after timing, the engine labored some and I had to raise the idle speed to specs.

                After raising the speed I rechecked and set the timing to 4 degrees BTDC.

                Using boat tach (I know not very accurate but that's all I've got, as the tach part of my dwell meter is missing the pickup lead that goes around the plug wire).

                DougV>

                Comment



                • #9
                  Re: dwell verses feeler guage merc 140 hp

                  For future searchers...

                  Setting the points gap is just that, setting the gap. It is a starting point only, it is not an accurate measurement of the actual dwell angle or percentage achieved. Dwell angle or percentage tells you exactly what the coil "sees" and reacts to as it builds then delivers the spark charge thru the secondary circuit. Using a dwell meter is the only way to be sure the ignition contact points are set correctly.

                  If you are just setting the gap and not checking the dwell afterwards then any mechanical deflections or deviations are not being accounted for and the actual dwell may not be in tolerance. That definitely affects how much spark is delivered. You must also check distributor timing with a points setup, changing the gap will move the timing around enough to need it checked or adjusted.

                  One incentive for checking and setting/resetting the points gap using a dwell meter is this: If the dwell can be set to exactly what it was the last time the timing was checked/adjusted then the timing will most likely not need to be adjusted this time. This does assume the distributor is in reasonably good mechanical condition.
                  1991 HydroSwift 2200 Cuddy Volvo Penta 570/DP
                  1980 Glastron SSV167 90HP Mariner

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                  • #10
                    Re: dwell verses feeler guage merc 140 hp

                    When you checked the dwell, did you read the correct scale on your dwell meter? There are seperate scales for 4,6, & 8 cylinder engines.
                    After setting the timing, you can set the basic timing, which has to be done at the proper idle rpm or the weights inside will advance the timing for the higher rpm.
                    Don S.

                    sigpic

                    Please, no PM's (Private Messages) regarding boat/engine problems.
                    That is what the forums are for.
                    Only forum/moderator issues will be answered in PM's.

                    Comment



                    • #11
                      Re: dwell verses feeler guage merc 140 hp

                      yeah I used the 4 cyl scale.

                      Rechecked and adjusted the timing after the idle was re set.

                      Thanks for all the responses.

                      DougV>

                      Comment



                      • #12
                        Re: dwell verses feeler guage merc 140 hp

                        Originally posted by djvan View Post
                        yeah I used the 4 cyl scale.

                        Rechecked and adjusted the timing after the idle was re set.

                        Thanks for all the responses.

                        DougV>

                        Did that cure the problem?
                        Don S.

                        sigpic

                        Please, no PM's (Private Messages) regarding boat/engine problems.
                        That is what the forums are for.
                        Only forum/moderator issues will be answered in PM's.

                        Comment



                        • #13
                          Re: dwell verses feeler guage merc 140 hp

                          Just when I thought i was close to the best a 140hp will do. The starter konked out. It is 7.23 am right now. My new starter is at the parts store but they don't open til 8.00. So I should know in a few hours. If it still misses I think I will put the old wires back on to test the bad wire theory. It didn't miss before I replaced the distributor, wires, point etc.

                          DougV>

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                          • #14
                            Re: dwell verses feeler guage merc 140 hp

                            UPDATE

                            Just got back from a sea trial.

                            Starter works great (hard to believe how sick the old one sounded) funny how when you replace a bad part you can't believe how you didn't notice how bad things were until the new part is installed.


                            Could not get the miss out of it right away, I switched each plug wire with a known good one, cahnged each plug individually with another new one.

                            I wound up closing the points gap some. After setting dwell I checked the gap and had .030 book calls for .022 to start. I split the difference @ .026, didn't have dwell meter with me to recheck, will do that later,(it looks as though it is going to be a beautiful day so guess where I'm headed?)

                            I may borrow somebody elses dwell meter and compare to mine.

                            Maybe that's the problem.



                            Thanks for all the help.

                            As usual this site and its many knowledgeable members have come to the rescue again.

                            DougV>

                            Comment



                            • #15
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                              Re: dwell verses feeler guage merc 140 hp

                              By changing the dwell you essentially changed the timing. I am assuming you didn't check the timing after you changed the dwell again.
                              1998 Wellcraft Eclipse 24 Cuddy
                              Volvo Penta Duo-Prop 7.4L "LK"

                              2006 Sun Tracker Party Barge 21
                              Mercury 90 4-Stroke FI
                              "Common sense is not very common"
                              "Failing to prepare is preparing to fail." -- John Wooden

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