92 Mercury 100 stall at low speeds

58 Alumacraft

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My 92 Mercury is hard to start unless you give it quite a bit of throttle and is stalling at low RPM. Idle speed is around 850......any ideas what would cause this?
 

Dave1027

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Re: 92 Mercury 100 stall at low speeds

You might want to try opening up the idle mixtures a 1/4 turn. My '88 100 hp would cough (lean pop) and die at idle if I had my idle mixtures too lean.
 

58 Alumacraft

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Re: 92 Mercury 100 stall at low speeds

Dave, my idle screw were out 2 turns when I started. I turned them back to 1 1/2 (where they should be) and not much change.
 

Dave1027

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Re: 92 Mercury 100 stall at low speeds

Does you motor cough when it dies?
 

Dave1027

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Re: 92 Mercury 100 stall at low speeds

No cough, just dies.
Perhaps the idle rpm is too low? What rpm does it idle at? Should be 700 in gear. If it's lower than that you need to turn the idle timing a little more advanced.
 

58 Alumacraft

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Re: 92 Mercury 100 stall at low speeds

Idle speeds is around 850. I did a compression check also...........all four cylinders are 130 lbs
 
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Re: 92 Mercury 100 stall at low speeds

How are your plugs burning? Any pics?

I see the 100, 115 I-4 Mercs have issues on their coils. The ferrite cores are essentially glued together to touch at the top. That thin area to either side will crack/break.

Take your coils off, peel back the rubber protector and look at those cores. They have to be siliconed to the coil itself, and the top taped pieces are where they crack.

More often than not, the ferrite cores crack somewhere, and the motor will still run. Higher speeds are better, low RPM gets compromised. But too many cracked will effect low speed greatly. Especially on the 2+2 like yours. It's only idling on the top 2 cylinders anyway. Top 2 cracked ferrites and your motor will tell you about it.

Here's some pics of a healthy used one.




If this doesn't help, we'll need more information such as- does fuel added help or hurt? are you looking at a timing light and seeing erratic spark? timing? spark plug colors/pics?
 
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58 Alumacraft

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Re: 92 Mercury 100 stall at low speeds

Thanks Anchor Marine, It does run great at higher speeds......I'll check the coils. The plugs look to be a little on the lean side.....the porcelain below the electrode is more white than brown.
 
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Re: 92 Mercury 100 stall at low speeds

Thanks Anchor Marine, It does run great at higher speeds......I'll check the coils. The plugs look to be a little on the lean side.....the porcelain below the electrode is more white than brown.

If that's the case, I'd also take a large fuel sample. Pump your tank with your primer bulb in to a clear glass container (jar, old coffer pot) You'll be able to see the water seperation if it does have a water intrusion.
Becasue if they are lean, then it's not a coil issue, it's a lack of enough fuel for some reason. A mis-firing coil makes a plug darker to black/oily. This is becasue the right fuel would keep being delivered, but the ignition couldn't burn it.
 

58 Alumacraft

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Re: 92 Mercury 100 stall at low speeds

Good info, thanks. Findings: The top two coils look good, fuel test shows no sign of water in about a gallon glass jar.
 

58 Alumacraft

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Re: 92 Mercury 100 stall at low speeds

Not sure what else to do except take off the carbs and inspect/clean.
 

58 Alumacraft

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Re: 92 Mercury 100 stall at low speeds

Update, it turns out the stator tested bad...........replaced the stator (red mallory style) running good.
 
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