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1955 hesitates/stalls on acceleration after idling

Started by craig-o, February 18, 2018, 11:46:38 PM

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craig-o

I hope this is a common symptom of a particular problem, but before I tear into the carb again, I thought I’d check for some carb wisdom.  The car is a stock/unmodified 1955 Series 62 CDV with the original Roschester 4 bbl carb.

Symptoms: after the vehicle is warmed up, in city driving, nearly always after idling smoothly at a stoplight for >30 seconds, when I take my foot off the brake and push on the accelerator, the car will hesitate, and often stall. It will always restart immediately. When cruising, it runs smoothly and accelerates without hesitation.

What I’ve done: I rebuilt the carb recently, including a new accelerator pump, and that seemed to fix the problem; for about the first 300 miles. But the symptoms have returned. 

If I idle at the stoplight in neutral, and blip the accelerator before dropping it into Drive, it takes off without hesitation.  I have a fairly new fuel pump, and I can confirm that the accelerator pump squirts fuel. Could it be the floats sinking and allowing fuel to overflow the fuel bowl? I have not verified the fuel pressure from the new(er) fuel pump. Would too high fuel pressure cause this symptom? What about a vacuum leak?
Craig Rodenberger
San Jose, CA
1955 Coupé deVille
1955 Jaguar XK140 OTS

The Tassie Devil(le)

G'day Craig,

If the fuel float was sinking and the carby was overflowing, the engine would start running very rich before it stalled due to flooding, it wouldn't start up as easily.

Possibly a vacuum leak at the Distributor, but you would need a Timing light to check that if you didn't want to undo the vacuum line.

A Distributor Vacuum Leak would cause the engine to run lean.

A not-so-good Accelerator Pump could cause it, but you say that is okay.

Sorry I cannot be more accurate, but hard over the internet.

Bruce. >:D
'72 Eldorado Convertible (LHD)
'70 Ranchero Squire (RHD)
'74 Chris Craft Gull Wing (SH)
'02 VX Series II Holden Commodore SS Sedan
(Past President Modified Chapter)

Past Cars of significance - to me
1935 Ford 3 Window Coupe
1936 Ford 5 Window Coupe
1937 Chevrolet Sports Coupe
1955 Chevrolet Convertible
1959 Ford Fairlane Ranch Wagon
1960 Cadillac CDV
1972 Cadillac Eldorado Coupe

Mike Josephic CLC #3877

#2
Hi Craig-o:

My first thought was the same as Bruce's -- accelerator
pump.  However, since you replaced that already we'll
go to the next thing.

What's your idle speed set at (RPM's) in drive?  If that's
too low she would tend to stall as yours does.  It should
be 400 RPM with tranny in Drive.  If it's already there,
try increasing it 50 RPM or so.  Measure that idle speed
with the car warmed up and OFF of the fast idle cam,
in Drive with handbrake set.

Also, again as Bruce stated, you may have a vacuum
leak.

Did you do anything else to the carb when you replaced
the accelerator pump?  Double check your work and see
if everything is connected back up as it should be.

Good luck and let us know how you're doing!

Mike
1955 Cadillac Eldorado
1973 Cadillac Eldorado
1995 Cadillac Seville
2004 Escalade
1997 GMC Suburban 4X4, 454 engine, 3/4 ton
custom built by Santa Fe in Evansville, IN
2011 Buick Lucerne CX
-------------------------------------
CLCMRC Museum Benefactor #38
Past: VP International Affiliates, Museum Board Director, President / Director Pittsburgh Region

walt chomosh #23510

Craig,
  I don't think this is your problem but let me tell you my experience with my 1955CDV with the Rochester 4GC carb. (by the way, I have a fresh spare that I even road tested....not for sale but I'll loan it if you want to troubleshoot)  One day I pulled out into the street and as I gassed the accelerator it fell flat on it's face. I noted that I could really nail it and all was well. I studied the service manual and it pointed to the power circuit. After pulling the carb and throughly cleaning EVERY passage,it ran great and all was well.(15yrs or so ago)
  Then one day a couple of years later I pulled up to a stop sign and it died. Naturally I drove straight home to solve the problem but never could find anything wrong! (I did write notes in my log book) So I continued to drive my Cadillac smiling and diggin the ride....until,one day years later,I pulled up to the SAME stop sign and it died again. Straight home for troubleshooting(I had forgotten about the previous incident....I have other toys to play with you know) and getting into my log book it came back to me. Turned out it was my throttle shaft leaking. I rebushed it and once again life was good. That was 5-6 yrs ago and she runs sweet since!....walt...tulsa,ok

Caddy Wizard

I seem to recall that in the 1955 Service Man bulletins there is a mention of this very condition and it being solved by fine tuning the idle mixture.  As you may know, there are three primary modes of operation for the carb.  First is with the throttle closed -- idle circuits dominate and there is little contribution from the mains.  At the other extreme, the throttle is fully or fairly open, mains dominate and the idle circuits are all but passive.  In the middle is the transition from idle to open throttle.  If the idle circuit is running a little too lean, the engine might still idle reasonably smoothly (although it might run a bit warm).  But the lack of contribution from the idle circuits to the transition during part throttle can cause the engine to be too lean when you are calling for acceleration, leading to stalling. 

Something like that.  I'd suggest you scour the Service Man bulletins for a tech tip like this...
Art Gardner


1955 S60 Fleetwood sedan (now under resto -- has been in paint shop since June 2022!)
1955 S62 Coupe (future show car? 2/3 done)
1958 Eldo Seville (2/3 done)

jaxops

Quote from: Art Gardner  CLC 23021 on February 19, 2018, 06:32:56 PM
I seem to recall that in the 1955 Service Man bulletins there is a mention of this very condition and it being solved by fine tuning the idle mixture. I'd suggest you scour the Service Man bulletins for a tech tip like this...
Art is right.  Here is a copy of the Thoro-Check Manual as a tuneup guide to hit all possible points (pardon the tuneup pun).
1970 Buick Electra Convertible
1956 Cadillac Series 75 Limousine
1949 Cadillac Series 75 Imperial Limousine
1979 Lincoln Continental
AACA, Cadillac-LaSalle Club #24591, ASWOA

Caddy Wizard

Quote from: Art Gardner  CLC 23021 on February 19, 2018, 06:32:56 PM
I seem to recall that in the 1955 Service Man bulletins there is a mention of this very condition and it being solved by fine tuning the idle mixture.  As you may know, there are three primary modes of operation for the carb.  First is with the throttle closed -- idle circuits dominate and there is little contribution from the mains.  At the other extreme, the throttle is fully or fairly open, mains dominate and the idle circuits are all but passive.  In the middle is the transition from idle to open throttle.  If the idle circuit is running a little too lean, the engine might still idle reasonably smoothly (although it might run a bit warm).  But the lack of contribution from the idle circuits to the transition during part throttle can cause the engine to be too lean when you are calling for acceleration, leading to stalling. 

Something like that.  I'd suggest you scour the Service Man bulletins for a tech tip like this...


I must be getting old -- the Service Man bulletin says that in early cars the problem might be the accelerator pump, the power valve, and the primary cluster.  They recommended replacement with a mid-year improved version of these parts. 

Still, check the idle adjustments carefully.  Try enriching the idle mixture just a tad and see if it helps.
Art Gardner


1955 S60 Fleetwood sedan (now under resto -- has been in paint shop since June 2022!)
1955 S62 Coupe (future show car? 2/3 done)
1958 Eldo Seville (2/3 done)

Lexi

#7
For what its worth, when I had my '56 Rochester rebuilt 2 or 3 years ago, the rebuilder almost installed the wrong accelerator pump. He claimed that even though the rebuild kit was accurate, the pump was not as there was a change which necessitated the installation of one that was slightly larger in diameter, as I recall him saying. He said he almost missed it, and believe he added that it affected only early carbs that year. I mention this as it seems to address your issue and perhaps is something to consider. Perhaps there was a similar problem with the 1955 model year, which Art also alluded to. Clay/Lexi

craig-o

Thanks for all the ideas.  I also connected with my non-Cadillac, but old car enthusiast friends and got some similar responses.

I will definitely check the vacuum lines - and will probably replace them all, as the last time I did this was around 2000/2001.  There are no obvious big leaks, but who knows, and vacuum line is pretty cheap.

The metal tag is still on the carb, and I used that number when ordering a rebuild kit from Mike's Carburetor Parts, so hopefully the accelerator pump is the right one.  (As an aside, the serial number for the carb corresponds to a Packard Clipper from 1955, but the base has the exhaust passage that I understand Cadillac specified to address an icing issue, so I'm not sure if this is the original or a replacement Rochester 4GC).  As I said, it ran smoothly without this problem for about 300+ miles over a few months, so not sure why this would pop up later if the accelerator pump was too small.

As for the idle mixture, a friend forwarded me an article published online (http://www.thecarburetorshop.com/Troubleshooting.htm), which described my exact symptoms, and had the same recommendation as the Service Man bulletin referenced (transition from the idle circuit, and described a condition called "puddling" which causes non-atomized gasoline to enter the intake manifold in this transition).  Thanks, Art!  I will pull out the dwell/tach meter and timing light and check idle speed and reset the idle and air mixture.

Lastly, a friend also suggested a condenser.  The last time I replaced mine was probably ~2001, and ~2,500 miles ago.  He had a similar experience with a Jaguar E-Type, although being a 4-speed manual, his symptoms were slightly different.  He also referenced an occasional cruising-speed miss, which, now that I think of it, I may have experienced as well, but it was so minor and intermittent, I just attributed it to poor road surface.  He finally solved his problem with a new Pertronix distributor; which I'm considering.  I've heard of, and experienced, recent poor replacement condensers with some other cars, so I may try a couple of sources and just buy a few.  Anyone have a recommendation on where they consistently get new, reliable condensers?

Walt, thanks for the offer, but I'll see what I can find before I take you up on your offer of a loaner.
Craig Rodenberger
San Jose, CA
1955 Coupé deVille
1955 Jaguar XK140 OTS

Jeff Rosansky CLC #28373

#9
Quote from: craig-o on February 20, 2018, 03:53:19 PM
The metal tag is still on the carb, and I used that number when ordering a rebuild kit from Mike's Carburetor Parts, so hopefully the accelerator pump is the right one.

I actually did the same thing with Mike's Carbs. Just because the tag is on there doesn't mean it is the right one. My tag was actually not the correct one for the carb I had.  I probably sent him 15 or 20 pictures of my carb. I used a micrometer on the accelerator pump and sent him a picture with the mic on it to avoid confusion. My carb was in bad shape (on the manifold with no gasket, only orange rtv. He was very helpful.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille

tripwire

Craig,
Don't change more than one thing at a time, otherwise you won't know what fixes your problem. 

Also, there has been a ton of bad condensers out there lately so test it before installing it.
Driving now:
2013 CTS4 Performance Coupe
1940 LaSalle 5229 C4D

A few I used to drive:
1976 Cadillac Ambulance
1969 Cadillac Hearse, Superior Body
1966 Buick Wildcat Hearse
1957 Ford Thunderbird x 3, 1 E code, 2 D code
1956 Oldsmobile Rocket 88 Sedan
1949 Mercury Convertible
1949 Mercury Coupe, Mild Custom
1936 Buick Special Sedan

CRAIG LEWIS

I had a similar isssue with my 53. Drove me nuts. evantually found it was the gasket between the manifold and the carb replaced it with correct one and all was fine from there.

Good Luck
Craig-L

Lexi

Good point. Sometimes wrong parts in kits or parts made incorrectly. A buddy damaged his '56 Cad engine when his improperly cut carb base gasket caused his throttle to stick wide open upon a cold start. That was on a dual quad Carter set up. Not the first time I have heard of this. Clay/LExi

Caddy Wizard

Art Gardner


1955 S60 Fleetwood sedan (now under resto -- has been in paint shop since June 2022!)
1955 S62 Coupe (future show car? 2/3 done)
1958 Eldo Seville (2/3 done)

Jay Friedman

Quote from: craig-o on February 20, 2018, 03:53:19 PM
I've heard of, and experienced, recent poor replacement condensers with some other cars, so I may try a couple of sources and just buy a few.  Anyone have a recommendation on where they consistently get new, reliable condensers?

A Washburn's Wisdom article in the Self Starter some months ago dealt with unreliable new condensers.  You can check with John Washburn, whose email address is in the CLC directory. 

The article recommended a condenser from the Madison Tractor Company for my '49.  I bought one and so far it has been working perfectly.
1949 Cadillac 6107 Club Coupe
1932 Ford V8 Phaeton (restored, not a rod).  Sold
Decatur, Georgia
CLC # 3210, since 1984
"If it won't work, get a bigger hammer."

craig-o

Update:
I thought I'd start off simple, so I replaced the condenser with an AC Delco that was purchased at my local parts supplier - they say it has a 1-year warranty, and will be replaced if I find it defective.  Unfortunately the weather did not cooperate, and I haven't been able to take her out for a test drive.  I don't know how to test a condenser off the car, so although I can confirm that it does start and run, I haven't been able to repeat the conditions.  Also unfortunately, I am travelling on business this week, and won't get another chance to pull her out of the garage until this weekend.

I promise that I will post follow-up.

Thanks again for all the help/suggestions.
Craig Rodenberger
San Jose, CA
1955 Coupé deVille
1955 Jaguar XK140 OTS

tripwire

Here's how to test a condenser:

1.) Remove the condenser from the engine (or at least disconnect the lead wire). Note the small metal connector located on the end of the condenser. This connector is the "hot" or power connection. The metal case of the condenser is the grounding point. Discharge the condenser by shorting the lead wire to the case.

2.) Switch the meter to the ohms position. Place the red lead into the "ohm" connector on the meter. Insert the black lead into the "com" or common connector on the meter. Set the resistance range to the highest available setting (if it is selectable). Connect the test leads together and zero the meter. If the meter won't zero replace the battery. (Yes, an ohm meter has a battery).

3.) Touch the red lead to the hot connector on the condenser. Place the black lead to the metal case on the condenser. The meter's needle should jump slightly to the right (toward 0-ohms), then should drop back to the left towards infinite resistance). Hold the leads in place for 15 to 20 seconds. This action places charge in the condenser. If the test shows any reading other than infinity, the condenser is leaking and needs to be replaced.

4.) Remove the leads and reverse the placement to the condenser. Move the red lead from the hot connector to the metal case, and move the black lead from the metal case to the hot connector. At the moment where both leads are touching the correct points, the meter should jump towards the right. The second time the needle may move twice as far, as this action discharges the condenser. Holding the leads in contact should again result in movement of the needle back toward infinite resistance.

5.) Movement of the meter's needle indicates the condenser is good. If no movement was indicated on the meter in any circumstance, the condenser is bad and must be replaced. Retest the condenser several times for a consistent reading.
Driving now:
2013 CTS4 Performance Coupe
1940 LaSalle 5229 C4D

A few I used to drive:
1976 Cadillac Ambulance
1969 Cadillac Hearse, Superior Body
1966 Buick Wildcat Hearse
1957 Ford Thunderbird x 3, 1 E code, 2 D code
1956 Oldsmobile Rocket 88 Sedan
1949 Mercury Convertible
1949 Mercury Coupe, Mild Custom
1936 Buick Special Sedan

craig-o

Thanks for the informative write-up, Wes.  I'll test the old one this weekend and see what I find.

Just curious to hear your thoughts on this from an academic standpoint.  It seems like these tests will result only in a pass/fail, since I'm just looking for needle movement, and not quantifying the result; is that correct?  As stated, this issue was intermittent, and idling was generally good.  Wouldn't you expect the old condenser to most likely give a positive result, if in practical experience, this miss was only once in every several thousand cycles?

Craig Rodenberger
San Jose, CA
1955 Coupé deVille
1955 Jaguar XK140 OTS

J. Gomez

Craig,

Test the condenser with Wes method (with an analog voltmeter) is just a pass or fail, it is not intended to show if the capacitance is within the posted range. To test the capacitance you will need a meter that is capable to test capacitance either a digital voltmeter or a capacitance meter only.

If by any chance you have the condenser and points all in one unit installed “trash them” go with the individual set.

Just for curiosity is you distributor vacuum advance working properly and does the distributor plate moves freely while operating or releasing the vacuum?

One thing from your notes that strikes my curiousity is;

Quote from: craig-o on February 18, 2018, 11:46:38 PM
If I idle at the stoplight in neutral, and blip the accelerator before dropping it into Drive, it takes off without hesitation.

When you blip the accelerator increasing the RPM slightly before putting it into drive there is no hesitation. That does not sound like electrical (points/condenser) issue to me,  ??? but other experts here can chime in.

Have you try to revving the engine slightly in gear when fully stop and see if the same condition persists?
J. Gomez
CLC #23082

Jeff Rosansky CLC #28373

#19
I replaced my coil over the weekend. Idled well. Backed out of the driveway just fine. Put in drive and hit the gas and it bucked horribly. Put the old coil in and it ran fine. Put another new coil in and had the same problem. Put the old coil back in and drove it tonite just fine.
So, check your coil.
Jeff
Jeff Rosansky
CLC #28373
1970 Coupe DeVille (Big Red)
1955 Series 62 (Baby Blue)
Dad's new 1979 Coupe DeVille