RE: IML: 71 carb problem

[David Whitney <hazegreen66@xxxxxxxxx>]

With a freshly rebuilt carb and electronic ignition you have eliminated many of the possibilites.

 

I concur with Robin that vacuum is the place to start.  Initial advance (at correct low idle RPM) is the timing that gives you the most vacuum.  When you mash on the accelerator pedal, you are changing the advance two ways -- first the vacuum advance, second the distributor's built-in mechanical advance.

 

Make sure you do not have a vacuum leak anywhere.  That will keep you busy for a little while.  Now you are in the right neighborhood to correct the problem, if it persists.  Next make sure the vacuum advance is working properly.  It is, by the way, adjustable, but for normal Imperial use that should not be necessary.

 

Oh, one more thing -- do the "aurora borealis" test.  In near-total darkness (not your enclosed garage, you'll get carbon monoxide poisoning), use a spray bottle to mist the engine compartment with water.  Look for arcing and sparking and correct as necessary. 

 

Finally, having done all those good things that should have been done regardless of what your symptoms are, you will arrive at the root of the problem to the best of my ability to diagnose via e-mail:  One of two things is happening -- first, the distributor's mechanical advance is not working properly; second, the distributor itself is not spinning properly on its shaft.  Since the car seems to work fine with gradual acceleration, I would concentrate on the mechanical advance.

 

Please do not skip directly to the distributor problem without doing the vacuum and electrical tests first.

 

Happy motoring,

 

David

Robin Giesbrecht <robings@xxxxxxxxxxx> wrote:

I will tell you what I would do. Whether you want to follow is your choice
but:

Put a vacuum gauge on it and see what manifold vacuum it pulls. It should be
close to 20. Set the timing to get max vacuum. If you cannot get 15 then
there is a vacuum problem which must be sorted out. If vacuum is good and
timing has been set to achieve max vacuum take it out and load the
engine(uphill at about 50 mph in third) and see if it pings. If it does back
off the timing till the pinging stops.That is where you want to be with
timing. If it is an AVS carb is the air valve for the secondaries free? Just
move it to the open position and let it close by spring pressure. Should be
smooth movement and should be fully closed at idle. Has anyone played with
the adjustment for the secondary air valve spring? This is a very easy
adjustment and critical for any wide open throttle performance. If the
adjustment is off for any reason the car will run like crap or not at all
when you open the secondaries.Thermoquad has a very similar arrangement.
Super tuning and Modifying Carter Carbs by Car Tech is a pretty good book
for reference.

Robin Giesbrecht
72 Imperial


>From: Bruce Stubblefield
>Reply-To: mailing-list@xxxxxxxxxxxxxxxx
>To: mailing-list@xxxxxxxxxxxxxxxx
>Subject: IML: 71 carb problem
>Date: Tue, 6 Sep 2005 09:18:23 -0700 (PDT)
>
>Hello list,
> The mighty 71 four-door (440) refuses to bend to
>repair attempts. The shop and I have spent a lot of
>time on this, but no soap. The mechanic I'm using is
>an older guy who is quite familiar with old
>carburetted cars. Though clearly not a brilliant
>diagnostician, he's solved a number of other problems
>on the car.
> The symptoms: From a standing start or from
>coasting at 0 to about 5 mph, flooring the accelerator
>results in "backfire" popping out the top of the carb,
>stalling or almost stalling. A slower, more gradual
>acceleration does not show this problem. Also, car
>surges or bucks intermittently on hard acceleration
>from a stop under a load, as in accelerating up a
>normal freeway onramp leading to an elevated road.
> In the last month or so, new plugs, spark plug
>wires and electronic distributor (mopar performance)
>have all been fitted. Scopes both in shop and onboard
>show normal electrical performance. Timing is
>perhaps 5 or 8 degrees retarded. Aside from this
>problem, runs fine on 87 octane regular. I also
>frequently run 91 octane premium.
> Carb (Carter, not a thermoquad) was just rebuilt,
>with a new accelerator pump done twice, with no
>improvement. The shop found a service bulletin in an
>old 69-72 Mitchells book which described a similar
>problem and gave a solution of re-boring some holes in
>the carb and changing some of the metering needles.
>Carb shop did this per the service bulletin, to no
>effect. Mufflers and resonators are new.
> Has anyone solved a problem like this? Do I
>have to buy a modern carb?
>
>Many thanks, all you geniuses.
>
>Bruce S
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> > From: "jsadowski"
> > Subject: Re: IML: Stowing jack in a '59.
> > Date: Mon, 5 Sep 2005 15:44:03 -0700
> > Reply-To: mailing-list@xxxxxxxxxxxxxxxx
> > This part should be an easy find from one of the
> > used parts vendors listed,
> > since it was used for so many years.
> > John
> > ----- Original Message -----
> > From: "Daniel M Wing"
> > To: ;
> >
> > Sent: Monday, September 05, 2005 9:52 AM
> > Subject: IML: Stowing jack in a '59.
> >
> >
> > > Hi,
> > >
> > > I remember my 1969 Dodge Coronet (and earlier
> > cars) had a coil spring
> > > that
> > > attached to a loop in the floor and to the tab on
> > the jack that fits into
> > > the
> > > bumper.
> > >
> > > To stow the jack, you lower the jack on the
> > notched post so that the
> > > spring will
> > > reach when you set the jack in place. Then you
> > jack it up until there is
> > > enough tension on the spring to hold the jack
> > secure.
> > >
> > > To remove, just reverse the jack and jack it down
> > until the spring comes
> > > loose.
> > >
> > > The spring is a separate part used only for
> > holding the jack in place.
> > >
> > > Dan Wing
> > > Marcy, NY USA
> > >
> > > imp1983@xxxxxxxx
> > >
> > > From: "jsadowski"
> > > Subject: Re: IML: Bumper Jack Stowage in Trunk -
> > 59 Imperial
> > > Date: Sat, 3 Sep 2005 20:14:34 -0700
> > > Reply-To: mailing-list@xxxxxxxxxxxxxxxx
> > > There is a spring that attaches in a loop in the
> > floor & the other end
> > > attaches at the part of the jack that raises. I
> > believe these are all the
> > >
> > > same at least back to 59 & through 66.
> > > John
> > > ----- Original Message -----
> > > From:
> > > To:
> > > Sent: Saturday, September 03, 2005 2:57 PM
> > > Subject: Re: IML: Bumper Jack Stowage in Trunk -
> > 59 Imperial
> > >
> > >
> > >> The tensions spring is a separate piece.
> > >>
> > >> Paul W.
> > >>
> > >> In an email dated 3/9/2005 8:08:07 pm GMT
> > Daylight time, Charles Hansen
> > >
> > >> writes:
> > >>
> > >>>The restoration of my '59 Imperial is nearing
> > completion and I'm trying
> > >
> > >
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> > From: Billimp68@xxxxxxx
> > Date: Mon, 5 Sep 2005 18:56:44 EDT
> > Subject: Re: IML: Your New 68 LeBaron
> > Reply-To: mailing-list@xxxxxxxxxxxxxxxx
> >
> > -------------------------------1125961004
> > Content-Type: text/plain; charset="US-ASCII"
> > Content-Transfer-Encoding: 7bit
> >
> > Mark,
> >
> > How about a run down on your new 68 Le Baron, you
> > know, mileage, colors, in
> > and out, options, etc, etc.
> >
> > Bill/Imp, 68's
> >
> > -------------------------------1125961004
> > Content-Type: text/html; charset="US-ASCII"
> > Content-Transfer-Encoding: quoted-printable
> >
> >
> >
> > > > content=3D"text/html; charset=3DUS-ASCII">
> > > > name=3DGENERATOR>
> > > > COLOR: #000000; FONT-FAMILY:=20=
> > Arial"=20
> > bottomMargin=3D7 leftMargin=3D7 topMargin=3D7
> > rightMargin=3D7>> > e_document=20
> > face=3DArial color=3D#000000 size=3D2>
> >

> > size=3D3>Mark,

> >

> > size=3D3> 

> >

How about a run down on
> > your new 68 Le Baron, yo=
> > u=20
> > know, mileage, colors, in and out, options, etc,
> > etc.

> >

> > size=3D3> 

> >

Bill/Imp,=20
> > 68's

> >
> > -------------------------------1125961004--
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> >
> > From: Crestonave@xxxxxxx
> > Date: Mon, 5 Sep 2005 19:16:39 EDT
> > Subject: IML: wire wheels
> > Reply-To: mailing-list@xxxxxxxxxxxxxxxx
> >
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>
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Happy motoring,

David

'91 K-Imperial driver
'66 Crown Coupe project
'66 LeBaron dual air and every option known to man

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