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Cold start

Started by 2danreed, September 08, 2019, 03:25:07 PM

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2danreed

Question regarding cold start on a stock 1964 429 engine. When I first start the car it fires right up, but after a few seconds the RPMs drop off and the car runs a bit rough. Slowly, the RPMs will rise after a couple minutes and smooths out once warmed up, then you can tap the pedal and kick the RPMs down to proper warmed-up idle speed. It just seems that something isn't right that the engine idles so slow and chugs, chugs prior to getting to the fast idle speed for warm up. Is there an issue with the choke?

Dan 
Dan Reed

Big Fins

It sounds like the choke pull off isn't opening the choke enough after the initial start to run the engine properly.

When you try with the air cleaner off, what do you see? The problem here is you only get maybe 1 or 2 tries a day to get it set right.
Current:
1976 Eldorado Convertible in Crystal Blue FireMist with white interior and top. (Misty Blue)
1969 Fleetwood Brougham in Chalice Gold FireMist with matching interior and top. (The Old Man) SOLD!

Past and much missed:
1977 Brougham de Elegance
1976 Eldorado Convertible
1972 Fleetwood Brougham
1971 Sedan de Ville
1970 de Ville Convertible
1969 Sedan de Ville
1959 Sedan deVille

Scot Minesinger

The way I'm thinking these cars are started (I have a Q-jet), is similar to 67-79 is you depress the gas pedal when cold once and crank.  It starts and goes into fast idle.  After 30 seconds to a minute you tap the gas pedal to drop it down out of that really fast idle to shift into gear.  At this point the car is cold and operating on a faster than warm up idle and the choke thermostat drops it into normal warmed up idle.

The way you start up procedure reads is that you are waiting until the car is warmed up to tap the gas pedal to drop it out of fast idle.

In any event as a first invetigation, check all the vacuum actuated devices as one may be ruptured and confirm you know all vacuum hoses are good.
Fairfax Station, VA  22039 (Washington DC Sub)
1970 Cadillac DeVille Convertible
1970 Cadillac Sedan DeVille
1970 four door Convertible w/Cadillac Warranty

2danreed

Thanks Big Fins and Scot.  The way it should work is that you pump the pedal once then turn the key and the engine should fire-up and run at fast idle - after a minute you should be able to tap the pedal and have the engine RPMs slow to normal warmed-up idle speed.

The exception here is once I turn the key and the engine fires up the RPMs quickly drop off and the engine runs too slow. As the engine warms the idle will gradually increase to an eventual fast idle speed, but it takes a few minutes to get there. Only once the engine is running at that fast idle can I then tap the pedal and have the RPMs drop to normal driveable range.

So in short, what I'm trying to diagnose is the fact my engine (at cold start) won't begin running at the fast idle speed like it should. To your point Big Fins, I haven't pulled the air cleaner off to see what's happening when I first start the engine, and to tell you the truth I don't quite know what I should be looking for.
Dan Reed

"Cadillac Kid" Greg Surfas 15364

I would check the choke setting and operation.Be sure all the choke linkage is free and the fast idle cam is free to turn on the shaft.  As you will find in the FSM, the cold idle speed is sett off the cam on the choke side of the carb. It does not take much of an adjustment to a working choke to bring it to proper operation.
Greg Surfas
Cadillac Kid-Greg Surfas
Director Modified Chapter CLC
CLC #15364
66 Coupe deVille (now gone to the UK)
72 Eldo Cpe  (now cruising the sands in Quatar)
73 Coupe deVille
75 Coupe deElegance
76 Coupe deVille
79 Coupe de ville with "Paris" (pick up) option and 472 motor
514 inch motor now in '73-

Daryl Chesterman

Dan, it sounds like the engine is running rich on cold startup, and this is indicated by the initial fast idle speed slowing down and the engine running rough.  If you were to observe the exhaust when this is happening, you would probably see black smoke coming from the exhaust pipes.  The first thing I would do is check the initial setting for the choke cover index.  You don't indicate whether you have a Rochester, or Carter Carburetor, but the Factory Service Manual will give you the specification for your carburetor as to what this setting should be.  If it is correctly set, the next thing I would do is have someone help you start the car while you observe what the choke butterfly is doing (after removing the whole air cleaner housing).  Set the choke by depressing the accelerator pedal once, have your helper start the engine, and observe what the choke butterfly does when the engine starts--it should open approximately 1/4 to 5/16 inch.  If it does not open that much, and the engine starts "chugging", manually open the butterfly a little and see if the engine speeds up and smooths out.  If it does speed up and runs smoother, you know what is causing your problem.  The fix for the problem will be determined by which carburetor you have and what the Factory Service Manual says about the adjustment for the choke pull off.  As Greg said, the linkage needs to operate freely.

Daryl Chesterman

2danreed

Thanks for the info Daryl and Greg. I just pulled the radiator to get it re-cored so once that is back at the end of the week I'll be able to dig into this issue again. And just FYI, my car has the Carter carburetor.

Dan
Dan Reed

Halcyondays

I certainly do not wish to insult you by telling you something you know, but be careful when starting a carburetor equipped car with the air cleaner off.  Although unlikely, there is the possibility of a backfire.  I once saw a backfire occur to a guy who was leaning over the fender looking at the choke action.  He was pretty close and lost his eyebrows.  Fortunately he wore glasses so his eyes were fine.  Sure was scary though.
Frank Mudge
Sedro Woolley, WA

1940 C 7567 CCP
1967 Impala SS CCP