Why does this '72 350 run so poorly when cold?

[Pete Phillips]

1972 LeSabre convertible, 350 cu. in. 2-barrel, a little over 60,000 miles. The engine sputters and runs on 4 or 5 cylinders following a cold start, and will barely run. Sounds like the carburetor is flooding it with fuel, as if the float is stuck, but I see no excessive fuel in the throat of the carburetor. The choke baffle is wide open all of the time, so it's not choking down, although that's also what it sounds like. No clouds of back smoke out the exhaust, though that's how it runs and that's what it sounds like. After trying to keep it running like this for 3 or4 minutes, all of a sudden, it settles down, runs like it should, and is ready to drive. Runs and drives perfectly the rest of the day. Then, the next morning, I go through this ordeal all over again.  What the devil could the problem be? It has confounded me for months and also confounded the two Buick restoration guys who work for me.

Photos to get attention.

Pete Phillips, BCA #7338

[EmTee]

15 minutes ago, Pete Phillips said:

Sounds like the carburetor is flooding it with fuel, as if the float is stuck...

 

16 minutes ago, Pete Phillips said:

The engine sputters and runs on 4 or 5 cylinders following a cold start, and will barely run. Sounds like

Maybe it's the opposite; too lean due to a vacuum leak (intake manifold or carburetor gasket).  When the manifold heats up the leak seals itself up.  Have you tried spraying some carb cleaner along the intake gaskets?  What happens if you choke it with the butterfly (or your hand) - does that help?

[JohnD1956]

I don't think the choke should be wide open when running at cold operating temp.  

[JohnD1956]

You may also want to verify your coil resistor wire for proper voltage. I know of an instance where thecresistor wire was only delivering 3 volts to the coil. 

[carbking]

QUOTE: "The choke baffle is wide open all of the time, so it's not choking down, although that's also what it sounds like." END QUOTE

 

This sounds like the problem; the choke plate SHOULD close for a cold start and effect the calibration for 4~5 minutes. The choke plate should slowly open as heat increases in the engine for 4~5 minutes. After than time the choke plate should be wide open.

 

Jon

Edited August 3, 2023 by carbking (see edit history)

[NTX5467]

Does this car perhaps have the "Max Trac" option, with a switch on the instrument cluster to turn it on and off?  Or were those a few model years before this?

 

Agree, on a cold start, the choke plate should not be full-open, but closed.  In our hot weather, perhaps not a hard-full-closed, but at least some closing initially.  At about 65 degrees F ambient (carb, engine, underhood air), the choke plate should JUST close consistently, then when the engine starts, the choke pull-off will pull it partially open so it does not choke too much.  Then the thermostat takes over as the intake manifold warms to open the choke plate the rest of the way to full-open.

 

If the choke plate is fully open at full-cold, see how much effort it takes to manually close it.  Perhaps the rod has disengaged from the thermostat itself or the coil spring has broken?

 

Just some thoughts,

NTX5467

[NC-car-guy]

2 minutes ago, NTX5467 said:

Does this car perhaps have the "Max Trac" option, with a switch on the instrument cluster to turn it on and off?  Or were those a few model years before this?

 

Agree, on a cold start, the choke plate should not be full-open, but closed.  In our hot weather, perhaps not a hard-full-closed, but at least some closing initially.  At about 65 degrees F ambient (carb, engine, underhood air), the choke plate should JUST close consistently, then when the engine starts, the choke pull-off will pull it partially open so it does not choke too much.  Then the thermostat takes over as the intake manifold warms to open the choke plate the rest of the way to full-open.

 

If the choke plate is fully open at full-cold, see how much effort it takes to manually close it.  Perhaps the rod has disengaged from the thermostat itself or the coil spring has broken?

 

Just some thoughts,

NTX5467

I disabled my max trac.  sounded like a problem waiting to happen.  But if it were the max trac, not sure how the temperature would affect that.

[NailheadBob]

Is the flap/valve stuck closed in the snorkel of air cleaner tube not allowing air to carburetor?

 

Bob

 

EDIT: OR flat/valve stuck open all the way to much air when cold engine

Edited August 3, 2023 by NailheadBob (see edit history)

[Pete Phillips]

Closing the choke baffle makes it run worse, and in this 90-105 degree weather, the choke is not needed when the engine is cold. Starts right up with a pump or two on the accelerator pedal after sitting overnight. I think it is something electrical that's temperature related. I went through the same ordeal this morning--sputter and sputter and acts like it is flooded with fuel, but it is not. Put it in gear and drove a couple of miles sputtering, and car would not go over 10-15 mph. For a split second it will get full power and try to accelerate, but only for a split second. As I approached my first destination, after two miles of this, it was as if someone flicked a switch and suddenly the car accelerated, got full power, and stopped the sputtering. Ran great for the rest of the morning. 

 

"Is the flap/valve stuck closed in the snorkel of air cleaner tube not allowing air to carburetor? "  Bob, good suggestion, but it does this with or without the air cleaner being in place on the carb.

 

No "Max Trac" accessory.

 

Pete Phillips, BCA #7338

 

Edited August 3, 2023 by Pete Phillips (see edit history)

[EmTee]

Change the condenser...

 

[NailheadBob]

As @EmTee said change condenser

look at and file ignition points also

 

did you touch ignition coil when acting up to see if is hot, and did you measure resistance on ignition coil

 

Bob

[MRJBUICK]

1 agree with NTX5467 that choke plate needs to be closed on initial startup and as he said the choke pulloff and coil will do the rest

dont let the ambient air temp fool you, the motor needs a rich mixture upon starting, this has to do not only with the air fuel mixture but atomization of the fuel in the intake manifold with the warmer mani temp as it warms up. with the plate open you are also not on the high idle cam which is needed because of what you are experiencing. ask any one who has a race car with no choke what their car runs like till warm. and yes once warm and the engine likes it it will suddenly run great. fix the choke first but as EmTee said try the condenser if it still runs bad those things are notorious pains lol

[NTX5467]

Thanks for the additional information and clarifications, Pete.  Agreed, minimal choke involvement with our current temperature range.  The flapper in the snorkel changes the SOURCE of the air going to the carb, not restricting it.  When closed, the source is from the heat stove baffling on the exhaust manifold for cold starts.  Perhaps the vac motor of that item is ruptured and results in a vac leak until the thermostat in the air cleaner cuts vac to it?  Unplugging and capping the vac source to that thermostat would decrease one heat-related issue, for diagnostic purposes.

 

Possible electric issues might be checked by swapping in a known good ignition coil, ballast resistor, and condenser.  Not new, but from a used distributor/engine, etc.?

 

Just some thoughts,

NTX5467

[Frank DuVal]

5 hours ago, NailheadBob said:

Is the flap/valve stuck closed in the snorkel of air cleaner tube not allowing air to carburetor?

Air still gets to the carburetor, it just takes a trip by the exhaust manifold first.

 

What's that old saying, 90% of carburetor problems are ignition?

 

The little gem of a fact is the engine suddenly ran good then went back to running bad. What is the ignition system, points/condenser or electronic something?

 

When reading the + coil terminal voltage, use an old analog meter if you do it with the engine running. Best to read it engine off and points closed.

 

 

Edited August 3, 2023 by Frank DuVal (see edit history)

[Pete Phillips]

FIXED IT!!!

Em Tee was right! The condenser was a piece of crap, new four months ago, and that's about the time I started having problems with this '72 LeSabre. I found a new old stock one for 1957-1960 Buicks in my parts stash, removed the "new" one yesterday afternoon, installed this new old stock, made in USA one, and the car started instantly this morning and ran perfectly. And I might point out, with the choke baffle wide open. You people who don't live in this Texas heat in August don't realize that a choke is completely unnecessary in this 100+ degree heat we have.

 

Lesson learned: 80% of all new condensers that you buy these days are made in China pieces of junk and just need to be thrown out!

 

Thanks to all for the various suggestions.

 

[NailheadBob]

Great news Pete, glad it is fixed

 

In the future if I have a car issue I will call @EmTee and @Frank DuVal first

 

Bob

[EmTee]

Glad you found it and that it was a simple fix.  Not so glad that it was yet another crappy condenser.  Hopefully the new old one will last a long time.  Converting over to Pertronix is starting to look better and better...  In the meantime I carry a 'known good' spare in the glove box. 

[Frank DuVal]

👍👏👍

 

Funny in a way, years ago (30ish) I bought the low cost made not in US points and condensers and used them in Corvairs with NO issue. It seems in the "low cost as only criteria" world a working part is not the goal of manufacturing......😟

Edited August 4, 2023 by Frank DuVal (see edit history)

[Pete Phillips]

And it was a major brand that was junk: Standard Automotive Products.

Pete Phillips

[rocketraider]

Exactly why I dig thru swap meets and elsewhere to find old stock ignition parts, any reputable brand. Stuff made before 1990 if at all possible. That's about time I noticed quality really going downhill.