86 OMC engine stumble

Joined
Oct 8, 2016
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I have an 86 OMC 4.3 stringer.
When running across the water I can make the engine miss/stumble when I use the trim switch or engine exhaust switch.
Trying to identify the most likely cause.
Thanks!
 

southkogs

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Welcome aboard:

New-you-boat, or did it just start doing this? Is the alternator puttin' out enough electricity?
 
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Oct 8, 2016
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I've had the boat for many years.
Did a complete rebuild of upholstery and tune up. Just started doing this this season .
I have a multi meter just wasn't sure where to start.
 

southkogs

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I would start with having the alternator tested. Not sure on an '86, but on my older 70s model the voltage regulator was a separate unit ... might have that looked at as well.
 

Scott Danforth

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Clean the battery terminals and cables. Youre provably getting a voltage drop when you use the trim
 
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Oct 8, 2016
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Sorry for the delay but just started back on the boat.
Battery tested bad so I replaced.
Tested in water and still stumble when using trim switch.
As far as I can tell, this set up doesn't have a resistor but does have a resistor wire.
Batt = 12.47 volts
Coil + to batt + (with points closed) = 7.28 v
Coil + to coil - = 4.32 v

The Clymer manual states " no more than 3.2 v drop" at coil to battery.

I guess the next step would be to have the alt tested but a test not running shows low voltage.
Could the voltage regulator be the cause?
There are only 2 wires on the + side of the coil.
1 from the starter and I believe the other is from the voltage regulator (difficult to get to)

Trying to address most probable with multimeter before tracing wires.
Thanks
 

Bondo

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Battery tested bad so I replaced.

Ayuh,..... Welcome Aboard,.... Did you sand to shiny metal Clean the new battery terminals,..??
How 'bout the connectors to the battery,..??
How 'bout the other ends of the battery cables,..??

My guess is, ya got a Bad ground path, causin' yer issues,.....

Btw,... If yer distributor has points, the voltages are correct,...
 
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Oct 8, 2016
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Yes replaced cable connectors to battery post and sanded/checked other ends to ground/starter.

Shouldn't the coil to battery test yield approx 9-9.5 v?
 

Maclin

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May 27, 2007
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6,761
Did you do anything just prior to when this began? Meaning the tuneup you mentioned, or the upholstery refurb? Just wondering if wiring was accidentally disturbed or similar. Like maybe coil was replaced, is wiring correct. If has tachometer connected to coil minus may try unhooking that temporarily.

I think 12v or 9v at the coil + from engine ground depending on if points open or closed. The 9v would indicate some sort of ballast resistance is in play, that is ok if the coil is marked as external resistance..
 
Joined
Oct 8, 2016
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Don't know of anything that's changed.
Coil is wired correct, dwell set with meter.
2 purple wires to + side of coil . One from starter and one from voltage regulator.
The tach is fluctuating which is the grey wire to - side of coil.
Is there a way to simulate the problem with multimeter on coil to measure the voltage drop?
Could the alternator and regulator. Be weak on losing output under additional load?
Trying to identify any more testing that may isolate problem area
 
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Oct 8, 2016
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When I compare the alt wires to the manual they are different.
All of the alt in the manual show a 2 wire system, yellow to regulator and orange to wiring harness connector.
My alt has 3 wires orange,purple and red.
I believe the purple and red are excitation and sensing.

I saw a previous post that says the purple and red switch at the splice at the alt.
Mine currently match at splice.
Can anyone please confirm?
The boat is listed as an 85 but I don't see the 4.3 in the manual until 86 and I think the 3 wire alt was on cobras around 88.

Thanks for the help.
 
Joined
Oct 8, 2016
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14
Checked timing.
2 degrees ATDC.
Set 4 degrees BTDC ( prem fuel).
Immediate improvement in performance.
Switched alt wires at splice. Tach no longer fluctuates.
Running great.

I must have connected alt incorrectly when cleaning after refurb.
Mis-matching red/purple wires at splice is not in my Seloc manual but I saw a diagram on another post on this forum.

Thanks for the help
 
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