Distributor Vacuum Advance Problem

I have an 87 Wrangler 4.2L I6 258 man. trans with the Carter BBD carb.
I recently replaced the exhaust manifold and replaced both the intake
and exhaust manifold gaskets. I also rebuilt the carb. even though it
was working fine, figured at 19 yrs old it was time. Upon completion I
noticed the engine would shudder ( a very low grumbling/coughing type
noise) at idle and during acceleration. And no it isn't the idler
tubes. This is all happening while in neutral, and far less noticeable
when driving under load.

I first thought I had an air leak in the intake manifold, which I
might. I also thought maybe I messed up the carb. rebuild, which again
is highly possible. However, when I disconnected and plugged the
vacuum advance at the distribtor to check the timing I noticed it was
idling and running smooth and consistent under acceleration again. So
this leads me to believe this is a distributor issue.

What does that dashpot/diaphram at the base of the distributor do
anyway? Are the plugs misfiring? Am I getting too much or too little
vacuum at the distr? The distr. cap, plugs and wires are all fairly
new, several years old but only have 1000 miles or so on them. The car
also has really bad knock and ping problems. Anyone have any ideas
what is causing this, your help will be greatly appreciated.
Thanks in advance,
Kevin

The advance plate and sleeve need regular lubrication. To do this you
remove the rotor and soak the pad below it in the tube with 10W30 oil.
You then manually work the plate to get the oil back in it.

The pot there should hold a vacuum when you suck on it.

If the computer sees a bad sensor somewhere, it will put the timing into
'limp home mode' and it will run like a bag of dirt.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Kevin wrote:
>
> I have an 87 Wrangler 4.2L I6 258 man. trans with the Carter BBD carb.
> I recently replaced the exhaust manifold and replaced both the intake
> and exhaust manifold gaskets. I also rebuilt the carb. even though it
> was working fine, figured at 19 yrs old it was time. Upon completion I
> noticed the engine would shudder ( a very low grumbling/coughing type
> noise) at idle and during acceleration. And no it isn't the idler
> tubes. This is all happening while in neutral, and far less noticeable
> when driving under load.
>
> I first thought I had an air leak in the intake manifold, which I
> might. I also thought maybe I messed up the carb. rebuild, which again
> is highly possible. However, when I disconnected and plugged the
> vacuum advance at the distribtor to check the timing I noticed it was
> idling and running smooth and consistent under acceleration again. So
> this leads me to believe this is a distributor issue.
>
> What does that dashpot/diaphram at the base of the distributor do
> anyway? Are the plugs misfiring? Am I getting too much or too little
> vacuum at the distr? The distr. cap, plugs and wires are all fairly
> new, several years old but only have 1000 miles or so on them. The car
> also has really bad knock and ping problems. Anyone have any ideas
> what is causing this, your help will be greatly appreciated.
> Thanks in advance,
> Kevin

Kevin wrote:
> What does that dashpot/diaphram at the base of the distributor do
> anyway? Are the plugs misfiring? Am I getting too much or too little
> vacuum at the distr? The distr. cap, plugs and wires are all fairly
> new, several years old but only have 1000 miles or so on them. The car
> also has really bad knock and ping problems. Anyone have any ideas
> what is causing this

Check for lean fuel mixture, get an air/fuel guage and tune the carb
with it.

Check for worn cam and lifters, if you find you can't advance the timing
much without knock, and it starts knocking with revs above 2k plug the
advance and run it... if you still get knock at higher RPM's; retard the
timing until it just idles smoothly (right before the retard causes
rough idle) if at that point you still can't totally eliminate the knock
when under load or revving higher than 2,000 RPM's then I'd bet on it
needing a new Cam and timing set.

I'm betting you had the same knock and ping problems before AND after
the carb rebuild and new gaskets right? Which caused you to do the work
in the first place. I bet it also starts horribly rough in winter but
much better in warmer months.

--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Air fuel gauge to tune the carb?????

ROTFLMAO! Man there isn't any 'fancy' way to tune that carb. If you
need a computer to tell you how to fix them you are screwed and should
not go anywhere near them.

For starts, his carb is not 'tunable', he has a computer running it.
The idle mix screws are supposed to be blocked with a plug. If it was
not put back exactly the same as before, it will run like a bag of dirt.

Now if he has the computer disabled, then it is a different story and he
should have stated this.

The computer also runs the timing and controls the advance
electronically. There is a mechanical and vacuum advance as well.

If any of the sensors have failed, it dumps the advance down for 'limp
home' mode. I suppose he could take a hammer and hit the manifold a
couple times to see if the engine stumbles. This would verify the
computer is still functioning with the knock sensor at least.

There is about a 15 degree difference in the base timing when the
computer is working and not working. With the computer in the loop, you
have to use the emissions sticker way to set the timing. I believe that
is a set at 1600 rpm with the vacuum line off so the mechanical advance
is full, not at idle like you do with no computer.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Simon Juncal wrote:
>
> Kevin wrote:
> > What does that dashpot/diaphram at the base of the distributor do
> > anyway? Are the plugs misfiring? Am I getting too much or too little
> > vacuum at the distr? The distr. cap, plugs and wires are all fairly
> > new, several years old but only have 1000 miles or so on them. The car
> > also has really bad knock and ping problems. Anyone have any ideas
> > what is causing this
>
> Check for lean fuel mixture, get an air/fuel guage and tune the carb
> with it.
>
> Check for worn cam and lifters, if you find you can't advance the timing
> much without knock, and it starts knocking with revs above 2k plug the
> advance and run it... if you still get knock at higher RPM's; retard the
> timing until it just idles smoothly (right before the retard causes
> rough idle) if at that point you still can't totally eliminate the knock
> when under load or revving higher than 2,000 RPM's then I'd bet on it
> needing a new Cam and timing set.
>
> I'm betting you had the same knock and ping problems before AND after
> the carb rebuild and new gaskets right? Which caused you to do the work
> in the first place. I bet it also starts horribly rough in winter but
> much better in warmer months.
>
> --
> Simon
> "I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Mike Romain wrote:
> Air fuel gauge to tune the carb?????

Don't be afraid of technology Mike, lean combustion and rich combustion
are measurable no matter if there's a carb providing the fuel or FI. Why
in the hell do you think his Exhaust manifold has an O2 sensor in it?

Anyone who's rebuilt a Carter BBD and left the POS controlled by the
computer (or more accuately the 19 year old poorly working early
emissions system) probably deserves the headaches they are sure to suffer.

--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Simon Juncal wrote:
>
> Mike Romain wrote:
> > Air fuel gauge to tune the carb?????
>
> Don't be afraid of technology Mike, lean combustion and rich combustion
> are measurable no matter if there's a carb providing the fuel or FI. Why
> in the hell do you think his Exhaust manifold has an O2 sensor in it?
>
> Anyone who's rebuilt a Carter BBD and left the POS controlled by the
> computer (or more accuately the 19 year old poorly working early
> emissions system) probably deserves the headaches they are sure to suffer.
>
> --
> Simon
> "I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Just gotta love this new breed of auto 'technicians'. LOL!

If they don't have a computer to tell them what is wrong they are
totally screwed.

It is just a 2 bbl carb there Simon, nothing to be afraid of and as I
mentioned if you need a computer to tell you what's up, you shouldn't be
anywhere near that BBD.

Mike
86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
88 Cherokee 235 BFG AT's
Canadian Off Road Trips Photos: Non members can still view!
Jan/06 http://www.imagestation.com/album/pi...?id=2115147590
(More Off Road album links at bottom of the view page)

Mike Romain wrote:
> Just gotta love this new breed of auto 'technicians'. LOL!
>
> If they don't have a computer to tell them what is wrong they are
> totally screwed.

This from a guy who see nothing wrong with needing to rebuild his carb
every year or so. I'm glad you are an expert on the carter BBD you'd
need to be to get decent performance out of it, me I have better things
to do than devote my life to the minutia of getting a piece of **** carb
to work well for short peroids of time between rebuilds, but you knock
yourself out.

By the way you forgot to answer to why there's an 02 sensor attached to
a carbureted jeep if it can't be used to tune a carb.

> It is just a 2 bbl carb there Simon, nothing to be afraid of

Absolutely right, just junk to be tossed aside in favor of better
designed, more flexible, more robust, more dependable, more precisely
controlled fuel injection.


--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Remember Mike's constantly out four wheeling, in an environment
most cars would fail. And you do know your fuel system wouldn't survive
a trip across Mexico. Yhy Daimler put the fuel filter inside the tank
I'll never guess, unless it's part of the demise of the Jeep name.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

Simon Juncal wrote:
>
> This from a guy who see nothing wrong with needing to rebuild his carb
> every year or so.
><snip>

L.W.(Bill) Hughes III wrote:
> Remember Mike's constantly out four wheeling, in an environment
> most cars would fail. And you do know your fuel system wouldn't survive
> a trip across Mexico. Yhy Daimler put the fuel filter inside the tank
> I'll never guess, unless it's part of the demise of the Jeep name.

My fuel filter is any 3/8th or smaller in/out in line filter off of just
about any GM or Ford vehicle made after 1986 (ie. throttle body
injection to present day MPI). My fuel system was not made by DC.

In my world, kooky make-believe challenges like going through freakin
mexico take a back seat to reliability, fuel economy, power, off-chamber
functioning, ability to adapt to major changes in altitudes etc.

In other words things that matter and are usefull every day are more
important to me than far fetched hypothetical BS

--
Simon
"I may be wrong, but I'm not uncertain." -- Robert A. Heinlein

Lucky you.
How many times have you changed your fuel filter, once every twenty
five thousand miles, as the book calls for? Your filter is hidden under
a shield along the frame rail. That is any fuel filter that will hold a
hundred pounds pressure.
This hypothetical BS is real if you live in San Diego.
God Bless America, Bill O|||||||O
http://www.billhughes.com/

Simon Juncal wrote:
>
> My fuel filter is any 3/8th or smaller in/out in line filter off of just
> about any GM or Ford vehicle made after 1986 (ie. throttle body
> injection to present day MPI). My fuel system was not made by DC.
>
> In my world, kooky make-believe challenges like going through freakin
> mexico take a back seat to reliability, fuel economy, power, off-chamber
> functioning, ability to adapt to major changes in altitudes etc.
>
> In other words things that matter and are usefull every day are more
> important to me than far fetched hypothetical BS