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  1. #1
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    Default 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. #2
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    Default 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.....

  3. #3
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    Default 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."

  4. #4
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    Default 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>

  5. #5
    Admiral ziggy's Avatar
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    Default 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'
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  6. #6
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    Default 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>

  7. #7
    Rear Admiral Fishermark's Avatar
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    Default Re: dwell verses feeler guage merc 140 hp

    Quote 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.

  8. #8
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    Default 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>

  9. #9
    Rear Admiral Maclin's Avatar
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    Default 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.

  10. #10
    Honorary Moderator Emeritus Don S's Avatar
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    Default 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.


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  11. #11
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    Default 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>

  12. #12
    Honorary Moderator Emeritus Don S's Avatar
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    Default Re: dwell verses feeler guage merc 140 hp

    Quote 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.


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  13. #13
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    Default 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>

  14. #14
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    Default 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>

  15. #15
    Supreme Mariner bruceb58's Avatar
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    Default 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.
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  16. #16
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    Default Re: dwell verses feeler guage merc 140 hp

    Reset timing after dwell change.

    DougV>

  17. #17
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    Default Re: dwell verses feeler guage merc 140 hp

    -------------------------------UPDATE -------------------------------

    With gap set at .026 runs great, but still misses after trimming up for max speed. (I think that just a few rpms more when doing this causes the previous symptoms)


    I reset the gap to .024 (that makes the dwell 34 deg.) I am still within specs for the dwell. Will sea trial later today. Hopefully if I am on the "edge" of a miss, when it starts to miss at WOT I'll know to check/replace the points.

    Speaking of points the set I bought has a lifetime guarantee on them. Anybody heard of that? I thought it was odd, asked the counter guy if they had to fail to get a replacement set and he said just bring them in when you think you need new ones and they'll give me some no quetions asked.

    The lifetime points were $22.00 (that's all they had in stock).

    I am quite sure this is going to alleviate my miss.

    I retimed after messing with the gap/dwell.

    Thanks for all the input from all of you knowledgable people.

    I check this site at least once a day sometimes 2 or 3 times.

    I think I would go through withdrawals if I could not.


    Thanks again and happy boating.

    DougV>

  18. #18
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    Default Re: dwell verses feeler guage merc 140 hp

    Adjustments to dwell or timing will effect idle... adjustments to idle will effect timing and vise versa...

    1) Set the point gap using feeler gauges (.022in or .5mm), this will get you close enough to start the engine...

    2) Start the engine and set the dwell using a dwell meter (28-34*)... allow the engine to warm to operating temp

    3) Set the idle speed with the engine idling, in gear IN THE WATER (650-700 RPM)

    4) Set the timing with the engine idling, in gear IN THE WATER (6* BTDC)

    5) Re-set the idle speed with the engine idling, in gear IN THE WATER

    6) Re-set the timing with the engine idling, in gear IN THE WATER

    7) If you made an adjustment during step 6, continue to adjust idle speed and timing until both are in spec



    If you do not have easy access to a lake, you can do 1-4 out of the water, hooked to the muffs... but the final idle adjustment will need to be done on the water...


    If all your adjustments are in spec, and you still have a miss start checking other things...

    Plugs (clean? properly gapped to .035in or .9mm )
    Wires
    Timing advance
    Coil (check primary and secondary resistance, secondary continuity, and the resistor wire)
    Condenser
    Point spring tension

    If everything above checks out good, you may want to check your charging system... too much or too little power to your ignition system and it will not function properly

  19. #19
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    Default Re: dwell verses feeler guage merc 140 hp

    I set all the stuff in the water before.

    But today I did it on the muffs.

    My book says 4 deg BTDC, Should be 6? (would the water make a diff on this?) I wouldn't think so. Maybe?

    About #2 I can only check dwell while running. I am forced to check, then adjust points and restart, then check it again or set it while cranking with the plugs out. (no window in the dizzy cap)

    Good point about the point spring tension, I suspect even though they are new they may need a little bend to give more tension.

    Appreciate the info.

    Heading to the lake in about an hour.

    Will see about the miss.

    DougV>

  20. #20
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    Default Re: dwell verses feeler guage merc 140 hp

    your initial timing should be 6* BTDC with your engine idling at 650-700 RPM... that is per Mercruiser manual #10

  21. #21
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    Default Re: dwell verses feeler guage merc 140 hp

    ok

    DougV>

  22. #22
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    Default Re: dwell verses feeler guage merc 140 hp

    I have a 86 4 banger also. The point is a 22 year old motor might not be setup to run as a brand new motor. Parts wear just a little i would think.

    In my own inexpert opinion each motor is different, right after they leave the factory. No 2 will run the same.

    Get yours to run as best as you can.

    Go out and enjoy it. Good luck

  23. #23
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    Default Re: dwell verses feeler guage merc 140 hp

    Just got back.

    All is good.

    I am very happy with it's performance.

    I know a 140 has never been known as a powerhouse but pretty much all we do is cruise to "our" island and the occasional tubing.

    Like chiefalen says it is a 22 year old boat, but we like it just fine.

    DougV>

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