Mercury Idle Stabalizer control

elbob54

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Nov 15, 2012
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Can Anyone out there discribe the working process of this control Stab? I don't understand How it effects the WOT timing. I've heard 2 different max advance settings 23 and 25 If this part is removed. I question how it's able to advance the timing when it's installed and functioning proper. Seems to me that once you have locked in the Max advance screw It's not going anywhere. With the Idle Stab installed max timing is set at 18. With it removed 23-25. How does the Idle Stab make up 5 to 7 degrees.??

The Motor is a 1986 Mercury 150 V6
V/R Bob
 

wired247

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Oct 8, 2011
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1,557
Re: Mercury Idle Stabalizer control

It doesnt make sense until you understand your motor has two separate coils in the stator that control the timing. They are staggered several degrees apart. The idle stabilizer shifts bias towards one or the other depending on RPM. At low RPM it shifts bias towards the higher advance coil to maintain a set RPM. At higher RPM over 5K or so it shifts the bias down to the lower coil to retard the timing in effect limiting the upper RPM level without the use of a hard rpm limiter. You can set the timing at 23 or 25 depending on what sort of gas you use and you might get a few hundred RPM on the high side even with the stabilizer attached. Without the stabilizer it just goes to your pre set advance setting of 23 or 25 and runs only on the high coil. It will run a little hotter in the chamber with the extra advance and might need slight re jetting to compensate for the extra spark lead at higher RPM if you run without the limiter.
 

Faztbullet

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Mar 2, 2008
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15,589
Re: Mercury Idle Stabalizer control

There are 2 types of modules...idle stabilizer and advance modules. A idle stabilizer such as your engine has ONLY works in the idle range rpm and if rpm starts to drop below 550 RPM it will advance timing up to 9? to keep engine from dieing. It does not advance timing at WOT rpm...so set your timing at 21? at cranking with it disconnected( so it doesnt advance at cranking RPM) which will give you 18? at WOT. The stabilizer works by varying the resistance to ground..
 

elbob54

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Nov 15, 2012
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Re: Mercury Idle Stabalizer control

The setting of 21 at cranking with Stab unhooked will give you 18 at WOT. So even if you re-connected the stab,18 will still be your WOT.

Stands to reason that if I set my timing at 25 cranking (Stab unhooked) I'd get 22 at WOT. 23 would be 20 at WOT? reguardless if I hooked the Stab back up?

Why would anyone set the timing at 23 or 25 (Stab hooked or unhooked) couldn't this be harmful to the engine?
 

Faztbullet

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Mar 2, 2008
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15,589
Re: Mercury Idle Stabalizer control

The setting of 21 at cranking with Stab unhooked will give you 18 at WOT. So even if you re-connected the stab,18 will still be your WOT.
Yep....
Stands to reason that if I set my timing at 25 cranking (Stab unhooked) I'd get 22 at WOT. 23 would be 20 at WOT? reguardless if I hooked the Stab back up?
That is correct as this ignition design will retard itself about 3? at WOT.
Why would anyone set the timing at 23 or 25 (Stab hooked or unhooked)
To get a little more hp and midrange grunt....works good on light boats under 1500lbs
Why would anyone set the timing at 23 or 25 (Stab hooked or unhooked) couldn't this be harmful to the engine?
Yes it could if precautions where not taken. You should have the 2 piece"hemi" head design chamber and these engine run a tad less timing due to the static pressure in cylinder when running. The max I would set your motor is 21? running(WOT).
 

jeff2c

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Feb 15, 2013
Messages
4
Re: Mercury Idle Stabalizer control

Faztbullet or someone else,

My 1986 v175 has the idle stabilizer Design 1. It is bad so I plan to do away with it. The service manual only describes that design as upping the timing if RPM hits 550 or below. I am also replacing the original switch boxes with CDI switch boxes. The Mercury service manual specifies 20 degrees BTDC WOT at cranking speed. Would you agree I should leave it at 20 BTDC WOT cranking speed rather than resetting it 23-25 per CDI's documentation? CDI documentation does not list different timings for different engines (seems odd). Thanks!

-Jeff
 

elbob54

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Nov 15, 2012
Messages
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Re: Mercury Idle Stabalizer control

I removed the stab control unit and did not advance the timing. Runs great! I would re-check the timing after you change switch boxes.
 

jeff2c

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Feb 15, 2013
Messages
4
Re: Mercury Idle Stabalizer control

I removed the stab control unit and did not advance the timing. Runs great! I would re-check the timing after you change switch boxes.
Thanks for the info. I think I will leave it alone since I believe the V175 design 1 idle stabilizer did not influence WOT spark advance.

I have seen Faztbullet recommend in other posts to set the timing on a V175 to 21 BTDC to split the difference as It was mentioned they came in 2.0 and 2.4 versions with different timings I guess.
 
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