dwell verses feeler guage merc 140 hp

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

MBAKER

Petty Officer 1st Class
Joined
Jun 9, 2008
Messages
275
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.....
 

xxxflhrci

Chief Petty Officer
Joined
Jun 14, 2008
Messages
637
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."
 

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

ziggy

Admiral
Joined
Jun 30, 2004
Messages
7,473
Re: dwell verses feeler guage merc 140 hp

don't forget to set the timing again after ya adj. the points. dwell effects timing.....
 

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

Fishermark

Vice Admiral
Joined
Oct 19, 2003
Messages
5,617
Re: dwell verses feeler guage merc 140 hp

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.
 

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

Maclin

Admiral
Joined
May 27, 2007
Messages
6,761
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.
 

Don S

Honorary Moderator Emeritus
Joined
Aug 31, 2004
Messages
62,321
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.
 

djvan

Chief Petty Officer
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May 3, 2003
Messages
411
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>
 

Don S

Honorary Moderator Emeritus
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Messages
62,321
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>


Did that cure the problem?
 

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

bruceb58

Supreme Mariner
Joined
Mar 5, 2006
Messages
30,454
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.
 

djvan

Chief Petty Officer
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May 3, 2003
Messages
411
Re: dwell verses feeler guage merc 140 hp

Reset timing after dwell change.

DougV>
 

djvan

Chief Petty Officer
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May 3, 2003
Messages
411
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>
 

freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
126
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
 

djvan

Chief Petty Officer
Joined
May 3, 2003
Messages
411
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>
 

freak007

Petty Officer 2nd Class
Joined
Jul 19, 2008
Messages
126
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
 
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