Spark plugs indicate lean mix on carbureted V6

Jack wrote:
>
> jim wrote:
> >
> > Jack wrote:
> >> Here is what I have concluded from input from posters here and from
> >> available info on the net and in various publications, including the
> >> shop manual for the 87 Dakota and the book entitled "Holley Carburetors
> >> and Manifolds" by Mike Urich & Bill Fisher, and from my own tests and
> >> observations.
> >>
> >> 1. For more than one reason, a white plug insulator does not necessarily
> >> indicate combustion temperatures over 2200F degrees or stoichiometric
> >> mix far outside the ideal of 14.7:1.
> >>
> >> 2. There are no vacuum leaks in the system.
> >>
> >> 3. I was finally able to induce a rich mixture by obstructing the air
> >> bleeds, so the carb is tunable.
> >
> > I expect this showed up as some shade of gray on the spark plugs? (black
> > would be the shade indicating extremely rich)
>
> It was a very, very dark shade of grey on the plug insulator, almost
> moist-looking. I had plugged the main air bleeds with small sewing
> needles and the larger idle air bleeds with a large paper clip. I had
> originally done this with the engine warm, first the mains, and then a
> high speed run and a quick shut down and pullover. I checked a plug and
> it was still white. I then plugged the idles and ran the same test and
> the plug was white. But after a complete overnight cool-down, the engine
> ran rough at startup. After a couple of blocks of slow driving I pulled
> over and pulled a plug. That's, when I saw the typical evidence of a
> rich mix. I want to try this again with the engine warmed up just to
> make sure that it is only a cold condition situation. Perhaps after
> warmup there is not so much of a need for full air bleed openings to
> deliver a good air/fuel ratio.
>
> >> 4. Coolant temperature, as indicated by the dashboard temperature gauge
> >> and the hand-on-radiator-hose test is normal.
> >>
> >> 5. Three inputs control the spark advance feature of the computer:
> >> coolant temperature, engine rpm and available manifold vacuum. I hooked
> >> up a timing light and observed the difference in the spark advance at
> >> cold start, partial warmup and full warmup for a given rpm. The spark
> >> advance increased as the coolant temperature rose. I also observed the
> >> spark advance increase with rpms for any given coolant temperature.
> >> Spark advance also responded to vacuum input to the vacuum transducer on
> >> the computer. Based on this observation, I am concluding that the spark
> >> advance feature of the computer is not non-functional. Based on
> >> performance and mileage I get I am concluding that it functions pretty well.
> >>
> >> 6. The idle contact wire does not affect spark advance, only air fuel
> >> mixture capabilities, which this carb does not have so it doesn't matter
> >> if it is properly routed (it was).
> >>
> >> I will use the present condition as a baseline. The floats are about
> >> 3/32 to 1/8 inch high and the jets are slightly oversized from stock.
> >> Before making any further mods, I will keep track of mileage and take
> >> the truck for a dry run at a smog check place.
> >
> >
> > Holley carbs often have a vacuum operated power piston. Lean condition
> > usually show up as surging with a vacuum power piston type carb. If it has a
> > mechanical linked power circuit then it is harder to tell. Usually if the
> > fuel metering is mechanical linked it is adjustable.
>
> Indeed, the power piston is vacuum operated on this model. But there is
> no surging. In fact, there are no driveability issues whatsoever. The
> *only* indication that the fuel mix might be lean are the white
> insulators on the plugs. I have great freeway mileage, 21.4 mpg on a
> recent 200 mile trip with a heavy lumber rack and a fully loaded 2x2x4
> foot tool box. This is with the original 3-speed automatic, no
> overdrive, that came on the first Dakotas. There are no flat spots and
> no hesitation whatsoever.

What happens is when the main metering is lean is as you accelerate from a
stop and that will cause a drop in vacuum sufficient to open the powervalve.
then as you get going the vacuum comes up and the valve closes that causes
the engine to go lean which produces less power and a drop in vacuum which
causes the valve to open again and then you get a surge of power and then
the vacuum comes up and the valve closes again and so on.



>
> As others in the thread have pointed out, alcohol in the gas may have a
> tendency to clean the plugs.

No you need something in the fuel to produce the tan color. Modern gasoline
is like white gas they used to sell in hardware stores for Coleman stoves.
Also, if the engine burns a little oil it will produce some tan on the spark
plugs. The alcohol replaces other components that boosted octane and may
have contributed some color on the plugs.
Add some Marvel Mystery oil to you gas tank - that should help with giving
your plugs some color.





> This prompted me to find out what the
> percentage of alcohol is in the gasoline in my area. It is 6% ethanol.
> So I am not going to worry so much about plug color for the present. I
> will reset the float to specs, leave in the larger jets and see what
> kind of reading I get on my next smog test. Based on that I will either
> replace the stock jets or put in a still larger size.

Probably you need to go the other way. Lean it out until you actually get
some indication it is running lean.

-jim


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jim wrote:
>
> Jack wrote:
>> jim wrote:
>>> Jack wrote:
>>>> Here is what I have concluded from input from posters here and from
>>>> available info on the net and in various publications, including the
>>>> shop manual for the 87 Dakota and the book entitled "Holley Carburetors
>>>> and Manifolds" by Mike Urich & Bill Fisher, and from my own tests and
>>>> observations.
>>>>
>>>> 1. For more than one reason, a white plug insulator does not necessarily
>>>> indicate combustion temperatures over 2200F degrees or stoichiometric
>>>> mix far outside the ideal of 14.7:1.
>>>>
>>>> 2. There are no vacuum leaks in the system.
>>>>
>>>> 3. I was finally able to induce a rich mixture by obstructing the air
>>>> bleeds, so the carb is tunable.
>>> I expect this showed up as some shade of gray on the spark plugs? (black
>>> would be the shade indicating extremely rich)
>> It was a very, very dark shade of grey on the plug insulator, almost
>> moist-looking. I had plugged the main air bleeds with small sewing
>> needles and the larger idle air bleeds with a large paper clip. I had
>> originally done this with the engine warm, first the mains, and then a
>> high speed run and a quick shut down and pullover. I checked a plug and
>> it was still white. I then plugged the idles and ran the same test and
>> the plug was white. But after a complete overnight cool-down, the engine
>> ran rough at startup. After a couple of blocks of slow driving I pulled
>> over and pulled a plug. That's, when I saw the typical evidence of a
>> rich mix. I want to try this again with the engine warmed up just to
>> make sure that it is only a cold condition situation. Perhaps after
>> warmup there is not so much of a need for full air bleed openings to
>> deliver a good air/fuel ratio.
>>
>>>> 4. Coolant temperature, as indicated by the dashboard temperature gauge
>>>> and the hand-on-radiator-hose test is normal.
>>>>
>>>> 5. Three inputs control the spark advance feature of the computer:
>>>> coolant temperature, engine rpm and available manifold vacuum. I hooked
>>>> up a timing light and observed the difference in the spark advance at
>>>> cold start, partial warmup and full warmup for a given rpm. The spark
>>>> advance increased as the coolant temperature rose. I also observed the
>>>> spark advance increase with rpms for any given coolant temperature.
>>>> Spark advance also responded to vacuum input to the vacuum transducer on
>>>> the computer. Based on this observation, I am concluding that the spark
>>>> advance feature of the computer is not non-functional. Based on
>>>> performance and mileage I get I am concluding that it functions pretty well.
>>>>
>>>> 6. The idle contact wire does not affect spark advance, only air fuel
>>>> mixture capabilities, which this carb does not have so it doesn't matter
>>>> if it is properly routed (it was).
>>>>
>>>> I will use the present condition as a baseline. The floats are about
>>>> 3/32 to 1/8 inch high and the jets are slightly oversized from stock.
>>>> Before making any further mods, I will keep track of mileage and take
>>>> the truck for a dry run at a smog check place.
>>>
>>> Holley carbs often have a vacuum operated power piston. Lean condition
>>> usually show up as surging with a vacuum power piston type carb. If it has a
>>> mechanical linked power circuit then it is harder to tell. Usually if the
>>> fuel metering is mechanical linked it is adjustable.
>> Indeed, the power piston is vacuum operated on this model. But there is
>> no surging. In fact, there are no driveability issues whatsoever. The
>> *only* indication that the fuel mix might be lean are the white
>> insulators on the plugs. I have great freeway mileage, 21.4 mpg on a
>> recent 200 mile trip with a heavy lumber rack and a fully loaded 2x2x4
>> foot tool box. This is with the original 3-speed automatic, no
>> overdrive, that came on the first Dakotas. There are no flat spots and
>> no hesitation whatsoever.
>
> What happens is when the main metering is lean is as you accelerate from a
> stop and that will cause a drop in vacuum sufficient to open the powervalve.
> then as you get going the vacuum comes up and the valve closes that causes
> the engine to go lean which produces less power and a drop in vacuum which
> causes the valve to open again and then you get a surge of power and then
> the vacuum comes up and the valve closes again and so on.
>
>
>
>> As others in the thread have pointed out, alcohol in the gas may have a
>> tendency to clean the plugs.
>
> No you need something in the fuel to produce the tan color. Modern gasoline
> is like white gas they used to sell in hardware stores for Coleman stoves.
> Also, if the engine burns a little oil it will produce some tan on the spark
> plugs. The alcohol replaces other components that boosted octane and may
> have contributed some color on the plugs.
> Add some Marvel Mystery oil to you gas tank - that should help with giving
> your plugs some color.

LOL! As much as I love the smell of MM Oil, I don't think it is worth
the money just to get colorful spark plugs.

I just finished a marathon web search relating to reading plugs. It was
a real eye opener. The subtleties involved are more than I realized and
the info that I grew up with doesn't always apply today. Most of the
sites are related to racing. Here are a couple that I thought were
extremely informative, especially for the photos:

Reading Spark Plugs
http://www.dragstuff.com/techarticle...ead-plugs.html

Plug Reading - Gas Engines - 4 Stroke
http://www.4secondsflat.com/Spark_plug_reading.html

Spark Plugs
http://www.dansmc.com/spark_plugs/sp...s_catalog.html

>> This prompted me to find out what the
>> percentage of alcohol is in the gasoline in my area. It is 6% ethanol.
>> So I am not going to worry so much about plug color for the present. I
>> will reset the float to specs, leave in the larger jets and see what
>> kind of reading I get on my next smog test. Based on that I will either
>> replace the stock jets or put in a still larger size.
>
> Probably you need to go the other way. Lean it out until you actually get
> some indication it is running lean.
>
> -jim

How might that indication present itself? Plug condition? Rise in
coolant temperature? Something else that doesn't cost money in a shop to
determine?

jim wrote:

> No you need something in the fuel to produce the tan color. Modern gasoline
> is like white gas they used to sell in hardware stores for Coleman stoves.
>

Actually, its nothing AT ALL like "white gas" that they used to sell for
coleman stoves. "White gas" was pure gasoline with no detergent or
antiknock additives which would foul and clog the gas-generator in
lanterns or stoves. Modern fuels may not have lead or manganese anymore,
but they have a whole witches brew of anti-knock and detergent
additives, oxygenates, and vapor-pressure modifiers.

Steve wrote:
>
> jim wrote:
>
> > No you need something in the fuel to produce the tan color. Modern gasoline
> > is like white gas they used to sell in hardware stores for Coleman stoves.
> >
>
> Actually, its nothing AT ALL like "white gas" that they used to sell for
> coleman stoves. "White gas" was pure gasoline with no detergent or
> antiknock additives which would foul and clog the gas-generator in
> lanterns or stoves. Modern fuels may not have lead or manganese anymore,
> but they have a whole witches brew of anti-knock and detergent
> additives, oxygenates, and vapor-pressure modifiers.

White gas is not pure gasoline. White gas or camp stove gas is almost pure
Naphtha.
Nevertheless, pump gas is like white gas with respect to the discussion
that was on going, which you snipped. The discussion was about why gasoline
burns without leaving color on the plugs. He made the point that ethanol
cleans the spark plugs. I was suggesting a better way to look at it is the
ethanol replaced the stuff that makes the spark plugs tan.

But now that you brought it up much of the gas sold in many parts of the
country is nothing but the refinery fractions plus ethanol. From what I have
read many refineries are meeting the required standard for regular mogas
without adding anything other than ethanol to the refined petroleum.

-jim

| Plug insulators are still snow white after all
| driving conditions.
What brand are these plugs ? NGK's insulators ( bigger & so
remain hotter ) can stay clean better than Champion / Denso.
Your plugs' heat range sounds correct.
http://www.ngksparkplugs.com.my/engl...21&Itemi d=64

| Any suggestions as to what might be causing this plug condition?
I believe insulators cannot get soot in dry air ; I used to drive in
0ºC dry air using Champion N9Y plugs, & once for 4 hr when
thermostat had overstretched & could not close so carb & engine
were too cold ( weak & coughing ) in 15ºC dry air, no soot @ all.
Now in 27-32ºC humid air, I have a soot problem to mitigate.

| Absolutely nothing makes sense.
Why worry w-o a problem ? Are you in dry air ? If exhaust has
a O2 sensor, 1 can connect a voltmeter & see if mix is lean.

jim wrote:

> Nevertheless, pump gas is like white gas with respect to the discussion
> that was on going, which you snipped. The discussion was about why gasoline
> burns without leaving color on the plugs.


Which is tantamount to saying that acetone is like water because both
are clear liquids...

>From what I have
>read many refineries are meeting the required standard for regular mogas
>without adding anything other than ethanol to the refined petroleum.

I seriously doubt that, although I suppose its possible to barely meet
the minimum standards that way since ethanol does have both limited
anti-knock and very good detergent properties.

Steve wrote:
>
> jim wrote:
>
> > Nevertheless, pump gas is like white gas with respect to the discussion
> > that was on going, which you snipped. The discussion was about why gasoline
> > burns without leaving color on the plugs.
>
> Which is tantamount to saying that acetone is like water because both
> are clear liquids...

> >From what I have
> >read many refineries are meeting the required standard for regular mogas
> >without adding anything other than ethanol to the refined petroleum.
>
> I seriously doubt that, although I suppose its possible to barely meet
> the minimum standards that way since ethanol does have both limited
> anti-knock and very good detergent properties.

They only need to start with 83 octane straight gas then add 10% ethanol to
meet the anti-knock standards. And ethanol is the only oxygenate additive that
is now in use. In regard to "barely meeting standards" - the term used by
refineries to describe doing anything else is "giveaway".

-jim

jinn wrote:

>>
>> I seriously doubt that, although I suppose its possible to barely meet
>> the minimum standards that way since ethanol does have both limited
>> anti-knock and very good detergent properties.
>
> They only need to start with 83 octane straight gas then add 10% ethanol to
> meet the anti-knock standards. And ethanol is the only oxygenate additive that
> is now in use. In regard to "barely meeting standards" - the term used by
> refineries to describe doing anything else is "giveaway".

For octane, yes. For vapor pressure, detergent function, long-term
storage stability, etc.... there are many shades of grey.