LeBaron Idle hesitation

1980 LeBaron, 318 auto, lean burn removed by previous owner. At idle the
engine seems to miss a beat every few seconds. Timing is set to 5 BTC, per
sticker. Port on carb that was for OSAC, seems to have no vacuum, at any
RPM, so I attached the vacuum advance on the dist to a spare port at the
base of the Carter carb (same place as on my 75 dodge truck). Measured
timing at 23 degrees at idle (vacuum line attached). If I retard the timing
to TDC (from 75 dodge manual) virtually no more missing, but also no more
power. Have oiled the felt in the dist, no change. Can't find any vacuum
leaks.
I can't figure out whats wrong here, car runs fine and has good power when
off idle. About 14,000 Km on this engine.

 

What's wrong is that you've now got the vacuum advance connected to
un-ported vacuum. Put it back on the port that originally had OSAC- you
should see vacuum on that port ONLY with the throttle opened somewhat.

Set the timing as follows:

DISCONNECT the vacuum advance line. Set base idle timing to whatever the
sticker says (usually TDC or 5 BTDC for a 318) at about 700 rpm (or
whatever the sticker says0. Then hook up the vacuum advance. THEN set
the idle speed.

 

Thanks for the post Steve

I reattached the vacuum line to the OSAC port. no vacuum up to 2500 RPM, as
measured with a vacuum guage.
Set RPM per label, 730 RPM, Set timing per label, 12 BTC.
No idle problem, and thats good, pickup is a little better. Dist timing
doesn't change till about 1300RPM then only about 8-10 degrees.
Never see anything from the ported vacuum outlet.
Is a carb rebuild in order at this point?

 

It may be a plugged ported vacuum passage. I'm not sure a total carb
rebuild is in order. Try flushing out the fitting with a spray can of
carb cleaner. If you can see the cleaner squirting in the throat of the
carb, the passage is open. Is the vacuum advance can diaphragm intact?
Test it by applying vacuum to the hose (suck on it, if you're not afraid
of the taste of gas fumes, use a hand vacuum pump otherwise ;-) and see
if it HOLDS vacuum. It might be leaking and still be able to apply
advance when hooked to straight manifold vacuum. The ported vacuum
signal is usually weaker and might not be able to "keep up" with a leaky
diaphragm.

 

Could be that. Could also be an incorrect carb gasket (between body
castings or between the throttle body and the manifold) blocking off the
passage that's suppose to supply vacuum to the spark advance port. Could
also be one of the many boneheaded "engineering changes" (hacks) one finds
in "remanufactured" carburetors. Bowl vents crudely disabled, linkages
crudely rerouted, passages plugged off with ball bearings driven in, etc.

DS

 

I know for a FACT that using the wrong carb base-to-manifold gasket with
a 2-bbl Carter (this is an 80s LeBaron, after all) will block ONE of the
vacuum ports. The problem is that I've been away from 2-bbl carbs so
long now that I can't remember for sure if its the manifold vacuum port
(I think it is) or the throttle vacuum port. But my vague recollection
is that the throttle (ported) vacuum nipple on those carbs is just
connected via a straight passage into a slot in the venturi wall right
above the throttle blades- no gasket. But still, incorrect gaskets are a
good thing to check.

There's always THAT possibility too, but I didn't really want to jump
straight there from the get-go :-/

 

Plugged it is.
Tried carb cleaner, no go.
Tried compressed air, no go.
Tried a 26 AWG wire, dead end about 1 1/4 inches in (I know, never stick
sharp objects in carb passages, it was copper, it was soft).

The opening is supposed to be above the throttle plate, according to the
manaul.
And yes, this is a rebuilt from "Auto-Line" (was on car when I got it).
Thinking of taking the carb apart and checking for wrong gasket, as
suggested.
The manaul's, cross section drawing doesn't show where this passage actually
is supposed to go. I'll check the venturi just above the throttle plate as
mentioned in the post.

Thanks for all the help.

 

What fun. Now you get to try and figure out where the obstruction is and
how to clear it!

Urg. Good luck to you.

Good plan. Get a good quality carburetor kit (e.g. Standard Hygrade).

Which manual are you using?

 

Just had another thought, and Dan you'll have to supply more info here.
I've lost track of whether this was originally a computer-controlled
feedback carb car or not. I know that its now running a standard
distributor so its at least had the ignition converted. My question is,
did the feedback carbs have the standard ported vacuum outlet? Or was it
blocked and only manifold vacuum sent to the transducer mounted on the
computer? Could this be a carb intended for use in a feedback system?

My brain hurts- peopl in my family have owned several of those cars, but
its been so long ago now that I just don't remember details like that. I
do remember the issue of a Carter 2-bbl needing a different base gasket
than an otherwise identical application Holley (the Holley gasket blocks
a port on the Carter carb)... but not the more subtle differences of
feedback vs non-feedback versions of the carb.

 

An '80? Pretty sure (but not 100%) that Feedback with O2 sensor didn't
start til '81.

Ooh, good question. Generally, the carbs that did not have a distributor
vacuum source on the inside -- didn't have a distributor vacuum nipple on
the outside!

There are some experiences so hellish that the human brain blots them out
in a desperate attempt to maintain sanity ;-)

 

No, O2 sensor.
The current installed carb has no wires coming out of it for computer
controls.
Factory service manual is from 1975, but all the wiring and hose locations,
appear to be the same as whats in the car (less the missing lean burn
system). If this carb was intended for a lean burn system, then I would
think this port would be blocked. By the way, this vehicle was serviced
only by a Chrysler dealer. I saw the paper work for it. They actually
rebuilt (or contracted out) the engine rebuild about 10,000 miles ago. They
would have been the ones that dumped the lean burn system.
There are two externally blocked manifold vacuum ports (and yes they are
functional). If I attach the dist to one of these ports the advance jumps
up to 23 degrees.
I have a spare carb for my 360, will it work on this 318, I guess
specifically, is the manifold bolt pattern the same.



There are two externally blocked manifold ports (and yes they are
functional)

 

OK, just dismantled the carb.
The OSAC orifice goes down to the bottom plate that has the throttle plates
in it. It passes through the gasket, into a small (about 1/8 x 3/16 x 1/4
deep) cavitty. The cavity has no exit. Nothing is blocked, there just
isn't an exit from this cavity. Even the gasket is solid around the hole.
Almost like the factory forgot to drill the hole into the venturi.

So, seeing as blocked is the normal condition, I figure a 1/16 th drill bit
might solve my problem. Worse case, I can always block it again.

Any ideas on a hole size for this port??

 

Eeek. Get a correct-year FSM. So many little details changed in the
vacuum system, carburetor, etc. that using a '75 book is *almost* worse
than using a Chilton, Haynes or no book at all.

Your 1980 car could very easily have been set up for manifold vacuum spark
advance right from the factory. It is a common but mistaken belief that
the spark advance port was always above the throttle plate at its idle
position.

Yes, the bolt pattern is the same.

 

The "moat" around the throttle bores, yes. That means this carb was set up
for manifold vacuum spark advance, *not* ported.

It's not supposed to. Vacuum is supplied to the moat via notches in the
carb-to-manifold gasket. The correct gasket looks like this:
http://partimages.genpt.com/partimages/182425.jpg


DS

 

Maybe I'm miss understanding you, but, the cavity is spearate from what I
would think a "moat" looks like. The cavity does not extend down to the
"carb to manifold" gasket (as you pictured, and thanks for that picture by
the way). It simple dead ends in the aluminum casting. Without physically
drilling a hole in aluminum, there is no exit. There certainly are several
other cavitys that sort of surround the the trottle bores. This cavity is
not open to any of them. This one definitly dead ends.

If I attach the vacuum advance to one of the manifold ports, the timing
jumps up to about 23 degrees. Then the engine "misses" about every few
seconds.

I'm wondering why, a carb would have a dead ended port tube, onto which you
could attach a dist vacuum line, were by the way, the dist was attached to
when I got the car.

Because this is a rebuild, I'm guessing that they got the throttle plate
sections mixed up, and installed one that was supposed to be for a non
ported carb.

So now the question is, what am I supposed to have?

Thanks for the help, I'm learning lots about carbs, all of a sudden.

 

AH, gotchya. Sorry, you were probably talking about a mating face between
the fuel bowl/venturi casting and the throttle body casting.

Tells us this carb is equipped with a throttle body originally set up for
no-vacuum-advance operation, as found on vehicles originally equipped
with ESA (Chrysler's Electronic Spark Advance). And that, in turn, tells
us a really old and yucky story about "remanufactured" carburetors. :-(

Mixed-and-matched carburetor castings. "Remanufactured".

Well, "supposed to"? You've already gone to a vacuum advance distributor,
so you need a carb that'll operate such a distributor correctly. One like
this: http://tinyurl.com/cz37u (Note this is a _rebuilt_ carburetor...a
single original unit carefully disassembled, cleaned, repaired,
recalibrated and reassembled. NOT an abusively-cleaned, "re-engineered",
thrown-together piece of junk "remanufactured" job).

 

Well, in this case it was a "yes and no."

Yes, every time I opened the hood on that gray shoebox of an 83 Gran
Fury, the mere sight of the sphagetti bowl of vacuum hoses caused me a
bout of acid reflux mixed with nausea.

On the other hand, the damn thing just ran, and ran, and ran, and ran,
and ran, and ran, and ran. Right up to over 200,000 miles, and no one
ever had to get deeper into the carb than changing the air filter. And
for that I'm eternally grateful, because I'm sure my language would have
turned the air 3 shades of blue if I'd been the one having to fiddle
with it... ;-) I learned the Holley vs. Carter base gasket difference
on a buddy's '84 pickup, but that was a non-computer non-feedback
application even as late as 84.

 

Well, I'm going to agree with Dan and say that an '80 was probably not a
feedback carb. But even if it WAS a computer-controlled application,
they did still have a vacuum advance signal that was fed to a transducer
mounted on the control computer. I just can't remember if that
transducer received the same (ported) vaccuum signal as a conventional
distributor, or if it received manifold vacuum. Theoretically, the
computer could use either one so long as the software "knows" what its
looking at.

In general, carbs do swap between a 318 and 360 if they have the same
number of barrels. Just watch out for the base gasket difference if
one's a Carter and the other's a Holley. Also the air-cleaner throat
opening may be a different size. Some 2-bbls used a larger air horn-
maybe even the same size as a 4-bbl, but I think there was an
intermediate size as well.

 

I think you hit the nail on the head

My experience is that 318s set up for manifold vacuum advance run like
cr*p. You have to close the throttle so much to get a decent low-speed
idle that they're idling on just a whiff of air/fuel, so the idle is
rough and torque-less (the AC engaging will drag it down enormously, for
example.) Also the off-idle response is *terrible* because the minute
you open the throttle a crack, the manifold vacuum staggers, the advance
disappears, and there's a huge transient until everything settles down
in a higher air-flow/less advance state. Which is pretty much the
symptom you described at the start of this thread. So even if the car
was "intended" for manifold advance, I'd take the opportunity to convert
it over to ported advance so that it'll actually run well.

 

Would have been manifold vacuum.
Doubt it had a feedback carburetor unless (possibly) it was
California spec.