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From: Mike Romain on 6 Dec 2008 10:10
Not being able to affect the mix or basically tune the carb is troubling
isn't it. When I see that, it usually implies a massive vacuum leak is
happening some place.

I also have seen strange things like that when the carb base plate got
put in upside down or with a torn gasket. Some base plates have notches
in them that direct the vacuum into the carb and when these go in wrong
or if the gasket goes in wrong, the carb's internal vacuum is messed up
which can make the carb not tunable.

Some carbs also like to just come loose at the base after a new install
and need the nuts re-torqued.

I think I would take a can of WD40 or carb cleaner and carefully spray
around the running carb's base and the intake manifold's gasket area to
see if I got an engine burp or miss. This would indicate a vacuum leak.

I would next pump the brakes like crazy when sitting at an idle to see
if that affected the engine. This would be to rule out a leaky power
brake unit.

Did your other carb just stop reacting to the inputs to the mixture
solenoid? Maybe the carb wasn't the trouble? Maybe the computer went
into limp mode because of something else gone bad like a leaky intake
manifold gasket or something?

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
'New' frame in the works for '08. Some Canadian Bush Trip and Build
Photos: http://mikeromainjeeptrips.shutterfly.com

Jack wrote:
>
> I have a brand new out of the box (not rebuilt) Holley 2280 replacement
> carburetor bolted onto a 1987 Dodge Dakota 3.9L V6 engine. The original
> was a Holley 6280, which is the feedback version of the 2280. The
> feedback solenoid for the 6280 is no longer available, so when mine went
> south, I opted for the 2280 as a replacement.
>
> I am getting snow white insulators on the plugs.
>
> I increased the main jets approximately 40%. No change.
>
> I backed out the idle mixture screws about 3/4 beyond lean best idle
> setting. No change.
>
> I raised the float level about 1/8 inch above specs. No change
>
> I decreased both the main air bleeds and the idle air bleeds by more
> than 50%. No change. Plug insulators are still snow white after all
> driving conditions.
>
> Manifold vacuum reads a perfect 19-20 inches Hg at warm idle. All lines
> pass a visual test and vacuum test.
>
> I checked the EGR system. It works perfectly. I have a vacuum meter
> hooked to the vacuum line that operates the EGR valve. It reads good.
> The temperature sensor that kicks in the vacuum soon after startup is
> working fine. Dashboard temp meter shows normal temp at all speeds and
> loads.
>
> Mileage on the freeway is great, over 21 mpg on a recent trip of 200
> miles. Mileage around town is so-so, 15 mpg tops (auto tranny). Truck
> has super heavy suspension with rack and big box of tools.
>
> Engine runs smooth and strong from dead stop to freeway speeds. No
> hesitation or flat spots anywhere. I have absolutely no driveability
> issues whatsoever.
>
> All ignition parts are new. Timing is dead on spec.
>
> How long should plugs be run before they turn toasty tan if
> stoichiometric is at 14.7 to 1?
>
> In another vehicle I have seen plugs turn from sooty under very rich
> conditions to toasty tan under correct conditions in a *very* short
> period of time, like minutes, not hours.
>
> Any suggestions as to what might be causing this plug condition?
>
> I am out of guesses. Absolutely nothing makes sense.
>
> Thanks,
> Jack
>
From: Don Stauffer on 6 Dec 2008 12:16
Jack wrote:
>
> I have a brand new out of the box (not rebuilt) Holley 2280 replacement
> carburetor bolted onto a 1987 Dodge Dakota 3.9L V6 engine. The original
> was a Holley 6280, which is the feedback version of the 2280. The
> feedback solenoid for the 6280 is no longer available, so when mine went
> south, I opted for the 2280 as a replacement.
>
> I am getting snow white insulators on the plugs.
>
> I increased the main jets approximately 40%. No change.
>
> I backed out the idle mixture screws about 3/4 beyond lean best idle
> setting. No change.
>
> I raised the float level about 1/8 inch above specs. No change
>
> I decreased both the main air bleeds and the idle air bleeds by more
> than 50%. No change. Plug insulators are still snow white after all
> driving conditions.
>
> Manifold vacuum reads a perfect 19-20 inches Hg at warm idle. All lines
> pass a visual test and vacuum test.
>
> I checked the EGR system. It works perfectly. I have a vacuum meter
> hooked to the vacuum line that operates the EGR valve. It reads good.
> The temperature sensor that kicks in the vacuum soon after startup is
> working fine. Dashboard temp meter shows normal temp at all speeds and
> loads.
>
> Mileage on the freeway is great, over 21 mpg on a recent trip of 200
> miles. Mileage around town is so-so, 15 mpg tops (auto tranny). Truck
> has super heavy suspension with rack and big box of tools.
>
> Engine runs smooth and strong from dead stop to freeway speeds. No
> hesitation or flat spots anywhere. I have absolutely no driveability
> issues whatsoever.
>
> All ignition parts are new. Timing is dead on spec.
>
> How long should plugs be run before they turn toasty tan if
> stoichiometric is at 14.7 to 1?
>
> In another vehicle I have seen plugs turn from sooty under very rich
> conditions to toasty tan under correct conditions in a *very* short
> period of time, like minutes, not hours.
>
> Any suggestions as to what might be causing this plug condition?
>
> I am out of guesses. Absolutely nothing makes sense.
>
> Thanks,
> Jack
>

The burned white insulators may be an indication of an overheating
problem. Lean mixture of course can cause heads and plugs to run hot,
but there are other causes of overheating in that area. Also, you might
try a cooler plug.
From: Jack on 6 Dec 2008 14:00
Mike Romain wrote:
> Not being able to affect the mix or basically tune the carb is troubling
> isn't it. When I see that, it usually implies a massive vacuum leak is
> happening some place.

All the symptoms seem to point in that direction, don't they?

I recently changed all the vacuum hoses, though, and did a thorough test
of each individual line and found no leaks, at least none that could be
characterized as 'massive'. Plus, vacuum reading at warm idle, at 700
rpm (spec) is steady at 19-20 inches Hg and there are absolutely no
driveability issues. I couldn't ask for better performance.

> I also have seen strange things like that when the carb base plate got
> put in upside down or with a torn gasket. Some base plates have notches
> in them that direct the vacuum into the carb and when these go in wrong
> or if the gasket goes in wrong, the carb's internal vacuum is messed up
> which can make the carb not tunable.

The thick *mounting gasket* for this carb is impossible to install
incorrectly. It's the same no matter which way you turn it. There is a 1
inch aluminum *spacer* that has and 'UP' arrow on it and it is pointing
up, if that is what you mean by 'base plate'.

> Some carbs also like to just come loose at the base after a new install
> and need the nuts re-torqued.
>
> I think I would take a can of WD40 or carb cleaner and carefully spray
> around the running carb's base and the intake manifold's gasket area to
> see if I got an engine burp or miss. This would indicate a vacuum leak.

All mounting bolts are tight and I used the purple Permatex high-tack
gasket sealant when mounting the carb. The intake manifold was remounted
by me about 30-40,000 miles ago when I re-did the valves. This white
spark plug condition did not arise until after I installed the new
non-feedback carb. It is basically the exact same body as the feedback
variety but with with minor modifications. The Holley 2280 is the carb
that Chrysler used for it's 318 engine from the early seventies until
carbs disappeared. The 3.9L engine in the 87 Dakota uses the 6280, which
is the feedback version. The mixture control solenoid is no longer
available and they wear out.

Chrysler refers to these carbs as "lean burn carburetors", so there may
be something in the design that causes a lean mix, But the only real
difference between this "lean burn" variety and the feedback variety
that came stock on this vehicle is the extra main jet controlled by the
mixture control solenoid, and the auxiliary idle air bleeds that are
also controlled by the mixture control solenoid.

>
> I would next pump the brakes like crazy when sitting at an idle to see
> if that affected the engine. This would be to rule out a leaky power
> brake unit.

I tested the brake booster by applying vacuum and observing vacuum
gauge. No leaks evident, but I will try your suggestion as it requires
almost no pain :--)

>
> Did your other carb just stop reacting to the inputs to the mixture
> solenoid?

The the mixture solenoid went bad. Small, molded rubber parts wore out
and residual magnetism caused it to get stuck in one position.


> Maybe the carb wasn't the trouble? Maybe the computer went
> into limp mode because of something else gone bad like a leaky intake
> manifold gasket or something?

Computer works fine. It's not in limp mode at all. Absolutely no
driveability issues with this carb. I got hold of the Chrysler breakout
box that reads the fault codes and tests the computer and solenoids for
this pre-OBD system. The problem was definitely with the mixture control
solenoid, no question about it. I monitored the signal from the computer
with a duty cycle meter and the signal was there even when the solenid
was stick and not responding to it. It would get stuck open or closed
and the the engine would stall when coming to a stop. The computer could
not see that it was stuck and continued to send the operating signal
based on input from the O2 sensor. I have been at this for years and I
have no doubt what caused the feedback carb to malfunction. It was
definitely the mixture control solenoid.

I guess I will have have to bite the bullet and yank the new carb, break
it down, check it out and reinstall it <groan>.

>
> Mike
> 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> 'New' frame in the works for '08. Some Canadian Bush Trip and Build
> Photos: http://mikeromainjeeptrips.shutterfly.com
>
> Jack wrote:
>> I have a brand new out of the box (not rebuilt) Holley 2280 replacement
>> carburetor bolted onto a 1987 Dodge Dakota 3.9L V6 engine. The original
>> was a Holley 6280, which is the feedback version of the 2280. The
>> feedback solenoid for the 6280 is no longer available, so when mine went
>> south, I opted for the 2280 as a replacement.
>>
>> I am getting snow white insulators on the plugs.
>>
>> I increased the main jets approximately 40%. No change.
>>
>> I backed out the idle mixture screws about 3/4 beyond lean best idle
>> setting. No change.
>>
>> I raised the float level about 1/8 inch above specs. No change
>>
>> I decreased both the main air bleeds and the idle air bleeds by more
>> than 50%. No change. Plug insulators are still snow white after all
>> driving conditions.
>>
>> Manifold vacuum reads a perfect 19-20 inches Hg at warm idle. All lines
>> pass a visual test and vacuum test.
>>
>> I checked the EGR system. It works perfectly. I have a vacuum meter
>> hooked to the vacuum line that operates the EGR valve. It reads good.
>> The temperature sensor that kicks in the vacuum soon after startup is
>> working fine. Dashboard temp meter shows normal temp at all speeds and
>> loads.
>>
>> Mileage on the freeway is great, over 21 mpg on a recent trip of 200
>> miles. Mileage around town is so-so, 15 mpg tops (auto tranny). Truck
>> has super heavy suspension with rack and big box of tools.
>>
>> Engine runs smooth and strong from dead stop to freeway speeds. No
>> hesitation or flat spots anywhere. I have absolutely no driveability
>> issues whatsoever.
>>
>> All ignition parts are new. Timing is dead on spec.
>>
>> How long should plugs be run before they turn toasty tan if
>> stoichiometric is at 14.7 to 1?
>>
>> In another vehicle I have seen plugs turn from sooty under very rich
>> conditions to toasty tan under correct conditions in a *very* short
>> period of time, like minutes, not hours.
>>
>> Any suggestions as to what might be causing this plug condition?
>>
>> I am out of guesses. Absolutely nothing makes sense.
>>
>> Thanks,
>> Jack
>>


--
"Sometimes we have Nyquil for dinner." -Dot Goddard
From: Mike Romain on 6 Dec 2008 17:08
Jack wrote:

> Chrysler refers to these carbs as "lean burn carburetors", so there may
> be something in the design that causes a lean mix, But the only real
> difference between this "lean burn" variety and the feedback variety
> that came stock on this vehicle is the extra main jet controlled by the
> mixture control solenoid, and the auxiliary idle air bleeds that are
> also controlled by the mixture control solenoid.

Isn't the intake different on the lean burn carb also? Or maybe the EGR
or even the cam is different? On my Jeep there are 5 flavors of EGR
that can be used according to other emission components. I had one lean
burn once and remember something odd about it, beside it not being able
to get out of it's own way.

Mike

From: Kevin on 6 Dec 2008 18:08
Mike Romain <romainm(a)sympatico.ca> wrote in news:493af7ae$0$26770
$9a6e19ea(a)unlimited.newshosting.com:

> Jack wrote:
>
>> Chrysler refers to these carbs as "lean burn carburetors", so there
may
>> be something in the design that causes a lean mix, But the only real
>> difference between this "lean burn" variety and the feedback variety
>> that came stock on this vehicle is the extra main jet controlled by
the
>> mixture control solenoid, and the auxiliary idle air bleeds that are
>> also controlled by the mixture control solenoid.
>
> Isn't the intake different on the lean burn carb also? Or maybe the
EGR
> or even the cam is different? On my Jeep there are 5 flavors of EGR
> that can be used according to other emission components. I had one
lean
> burn once and remember something odd about it, beside it not being
able
> to get out of it's own way.
>
> Mike
>
>

I would be the only one here to believe it was fine and dandy all
along. the new carb was ok, unless you have another indicator other than
the plugs it is lean, I doubt it is. white plugs unless bubbled are
common with todays gas. get a airfuel ratio check if you must, but I bet
it was ok before you started messing with it. KB

--
THUNDERSNAKE #9

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