Very Strange Problem

[Jon S]

 I took the 1958 out for a ride today and it performed perfectly to the point you cannot even feel the engine idling.   I parked the car for a few minutes and picked my son up for a ride and it continued to perform perfectly.   We returned and I turned it off and left it for about an hour before I restarted it for my trip home.   About a half a mile from his house it stalled at a red light but re-started and I didn't think too much about it although it's never stalled before.

From that restart on it stalled at every red light and was shaking very roughly before it stalled.   I pulled over and set the idle screw up and also turned the air horn out a turn and a half to keep the idle higher.   I limped home by giving it gas and brake at the same time coming to a stop.  At home I checked for vacuum leaks and found nothing and also removed the idle air screws and squirted Gumout in both passageways and reinstalled the screws.  I started it in Park and it ran smoothly for about three minutes with the choke wide-open and then started shaking and eventually died.

If I throttle the gas it will keep running but if I let go of the accelerator linkage it shakes and dies Like it is starving for gasoline or a vacuum leak. Fuel filter is clear and if I rev the engine it takes the gas fine.

I'm thinking there may be something in the carburetor from the gasoline causing a problem but then why would it run for five minutes before it starts shaking with the choke wide open the whole time?   Before I pull the carburetor apart, I am looking for some advice.

Any ideas?

["Cadillac Kid" Greg Surfas 15364]

Jon
First things I would check would be the vacuum advance and the timing/dwell.
Greg Surfas

[Clewisiii]

I had this same issue with a car.  It had somehow skipped timing. All the way home it was gas and brake on each light. Then it bent all the valves on one side and seized.

[Jon S]

Vacuum advance is working fine and timing is fine as well as Dwell.

[35-709]

Needle sticking shut in it's seat not allowing fuel to enter the float chamber(s)?  When it happens, tap the side of the carb  with a screw driver handle or small plastic headed hammer and see if that helps.

[Jon S]

What I did notice of interest is that when it stalls there is a flume of white smoke in the primary side of the carburetor which I'm assuming is gas vapor but I've never seen that before. Sounds like too much gas/flooding?

[signart]

I would start it and let it run, with breather off. Have your flashlight handy, as soon as it dies, peer down the carb and work the throttle. You need to determine if there is fuel in the bowl and getting a good stream before taking things apart and making adjustments.

[35-709]

What I did notice of interest is that when it stalls there is a flume of white smoke in the primary side of the carburetor which I'm assuming is gas vapor but I've never seen that before. Sounds like too much gas/flooding?

Could be, I was following your first thought that it was starving for fuel.  Could still be the needle and seat, but in this case the needle would not be sealing and allowing too much fuel in.  Could also be the floats sticking, again a light tap on the carburetor's side should produce some sort of better results if the floats are sticking.

[cadillactim]

Sounds like too much fuel or too much air throwing off the fuel/air mixture. Does a higher RPM keep the engine running smoothly? If so check for too much fuel. Maybe the needle is not seating allowing fuel to continue to enter the carb. With it running rough place cup your hand gently place it over the carb. If the engine smooths out you likely have a vacuum leak.

Tim

[bcroe]

Stuff a Wide Band OX sensor in the exhaust and instantly learn
if it is running lean.  Cheap enough in modern times, I have these
permanently installed 2 cars.  Also a fuel pressure gauge.

good luck, Bruce Roe

[Jon S]

Sounds like too much fuel or too much air throwing off the fuel/air mixture. Does a higher RPM keep the engine running smoothly? If so check for too much fuel. Maybe the needle is not seating allowing fuel to continue to enter the carb. With it running rough place cup your hand gently place it over the carb. If the engine smooths out you likely have a vacuum leak.

Tim

I'm beginning to think it's a stuck/binding float.  While running, closing choke slightly slows engine down and makes it want to stall, so that should rule out vacuum leak. Will check the floats and needle/seat tomorrow

[Roger Zimmermann]

Interesting issue. How can a device perform perfectly for some time and suddenly not? I'm wondering what you will find. I doubt that the timing can change during a drive (or after the drive with your son), but something in the carb can be wrong for whatever reason.

[James Landi]

Yes, yes, if the float is getting stuck, it may well be doing so on "the way up and on the way down"  thus both starving and flooding the engine... same problem could be much more arcane-- at the needle valve where a small "hairlike" piece of metal is lodged in the seat.  I've had that happen as a consequence of  checking the final filter screen on that fragile potmetal carburetor body that mates with the brass screen retainer.  In my case, the piece of metal was a tiny "eye lash" of metal wedged in the needle valve seat.  Hope this helps, James

[fishnjim]

Mileage?
I'd check the fuel pump and it's push rod.   They're notorious and will stick. 
I eventually changed to electric FP when I could not get new mechanical ones to last or work.   Same thing, wouldn't idle, stall out at the lights - before and after rebuild.   I had three different carb set-ups and rebuilt/dyno tested, so it's probably not the carb as it seems to be responding with screw adjustments.
I agree with Bruce, monitoring the exhaust is a good way to tell if things are functioning and to adjust the carb.   
And I keep gauges; fuel P, vacuum, voltage, and tach on these era cars.  Helps diagnose quicker.   "onboard diagnostics" of the day...
If it stalls out and "puffs" back through the carb, that's "normal", you're seeing unburnt fuel mix in the manifold being pushed out by piston through an open intake valve.  aka coughing.

[Jon S]

Well I took the carburetor apart and found nothing wrong but changed the needle and seat and accelerator pump and now it runs and seems fine. Go figure.

[35-709]

   I figure needle and seat, no surprise.

[Big Fins]

When I read the original post, that is what I thought too, but then others were trying to get you to rebuild the entire engine, so I gave up on the thread.

[Lexi]

Well I took the carburetor apart and found nothing wrong but changed the needle and seat and accelerator pump and now it runs seems fine. Go figure.

Well done Jon! Clay/Lexi

[walt chomosh #23510]

Jon,
  I had the exact same issue with my 55! In my case, the rear throttle shaft had wear which led me to installing a shaft bushing. (I sent the carb to daytona and had it back the same week!) An interesting point was that my car stalled at a stop sign which resulted in my bring it home and checking EVERYTHING (almost), only to find NOTHING. All was well until approx 2-3 years later it did the same thing at the same stop sign! (this is a car thats drive often!)  This time I looked at the throttle shafts and noted the secondary had "play". That's what led me to the pros and I was very pleased with their work.....walt...tulsa,ok