63 _ Engine dies at idle after warm up

[Timothy B.]

Re: 63 _ Engine dies at idle after warm up

Check the archives for a procedure to check for vacuum leak at the intake manifold and head interface. Could the carburetor be dirty inside, try to think about what changed. No symptoms with this carburetor before the tear down?

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

No carburetor problems before.

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

Is there a condition or conditions that could exist in the carburetor itself that would cause the dwindling vacuum with temperature?

[Timothy B.]

Re: 63 _ Engine dies at idle after warm up

Steve,

Best I can think of, no except the base gasket. Are you saying at IDLE speed when the engine is cold there is 11-12" vacuum then when warm at idle speed there is only 8" vacuum.

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

The base gasket is in place. Correct, vacuum falls off with increase in temperature. Something is obviously (or at least apparently) opening up with temperature.

[Stuart F.]

Re: 63 _ Engine dies at idle after warm up

What intake manifold do you have? (Year and material, exhaust crossover or not, heat riser or not, etc.)

Stu Fox

[Mike T.]

Re: 63 _ Engine dies at idle after warm up

I wonder if the heat riser is actually opening once the engine is up to temp? Relatively easy to check.

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

It is GM aluminum ( A similar one on Ebay has PN 3890490 and says 66-67). No heat riser. Cross-over restrictors in intake gaskets.

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

Update_ This thread has drifted to one titled LT1 cam idleSpurred by Tim's comment about a larger PCV valve, I removed the valve and connected a hose from the carburetor to the vent. In this configuration it will idle at 900 with the primary plates set as described and timing (B-28 can attached) at 30 deg. Eureka! That is the good news (the really good news!). The old news is that it still dies after idling for 15 to 20 mins. But, after it died, I removed the hose from the carburetor and restarted the engine. It ran for 10 mins with out dying; previously, it would die in 1-2 minutes after restart. As a further experiment, while it was still running I reconnected the hose, and as soon as I got the tip of the hose on the fitting, the engine immediately died. I repeated this a couple of times (start with no hose, connect hose, die) with the same result each time.

The previous hypothesis was that the engine is dying at idle from a too-lean condition caused by a vacuum leak that begins after warm up. But now it appears that it is dying from lack-of-air after warm up. Any theories about what could cause that? While you ponder that, I'm going to restart with the hose disconnected and see how long it will run. (It ran for 25 minutes without dying before I killed it. Then it started right up on half a crank)

[Duke W.]

Re: 63 _ Engine dies at idle after warm up

Spurred by Tim's comment about a larger PCV valve, I removed the valve and connected a hose from the carburetor to the vent.

It's not clear to me what you did, and I don't know the configuration of the PCV system.


Using a production '63 L-76 as a reference, perhaps you can describe the system and how you modified it this way, in the direction of flow beginning with the fresh air inlet:

air filter - inlet on oil fill tube - crankcase - exit at rear of block - valve - carb



Duke

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

The rear vent beside the distributor (draft tube ?) is connected by hose to the air cleaner. The PCV valve is connected inline between the PCV fitting on the front of the carburetor and the fitting on the oil fill tube by two hose pieces. When it would not idle in this configuration, I removed the valve and hose pieces and replaced them with a single hose. It will idle in this configuration before warm up, but after warm up it will die. When it dies after warm up, I can remove the hose, and in this configuration (carburetor PCV fitting open to the atmosphere) it will start and run without dying. (Longest test 25 minutes, after which I turned off the ignition and killed it; then on restart, it started immediately)

Steve

[Joe C.]

Re: 63 _ Engine dies at idle after warm up

The rear vent beside the distributor (draft tube ?) is connected by hose to the air cleaner. The PCV valve is connected inline between the PCV fitting on the front of the carburetor and the fitting on the oil fill tube by two hose pieces. When it would not idle in this configuration, I removed the valve and hose pieces and replaced them with a single hose. It will idle in this configuration before warm up, but after warm up it will die. When it dies after warm up, I can remove the hose, and in this configuration (carburetor PCV fitting open to the atmosphere) it will start and run without dying. (Longest test 25 minutes, after which I turned off the ignition and killed it; then on restart, it started immediately)

Steve

What you did was create a huge vacuum leak. This will dramatically increase idle speed and cause the mixture to go lean at all times. This is not related to your problem. Install a properly sized PCV valve such as an AC CV726.

You talk about vacuum decreasing when the engine heats up. Decrease in vacuum is proportional to engine speed decrease. It is not a vacuum dropoff that is your problem, but it is an idle speed decrease, which causes the vacuum to drop before it stalls.

There is a problem either with your carburetor, your advance weights, your vac advance diaphragm, or a combination of all three.

[Duke W.]

Re: 63 _ Engine dies at idle after warm up

The rear vent beside the distributor (draft tube ?) is connected by hose to the air cleaner. The PCV valve is connected inline between the PCV fitting on the front of the carburetor and the fitting on the oil fill tube by two hose pieces. When it would not idle in this configuration, I removed the valve and hose pieces and replaced them with a single hose. It will idle in this configuration before warm up, but after warm up it will die. When it dies after warm up, I can remove the hose, and in this configuration (carburetor PCV fitting open to the atmosphere) it will start and run without dying. (Longest test 25 minutes, after which I turned off the ignition and killed it; then on restart, it started immediately)

Steve

That's not the standard '63 PCV configuration, but maybe something similar to later in the sixties. One thought that I had: Could the PCV valve be installed backwards?

Duke

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

I understand that now. The fact that adding air (by disconnecting the hose) prevents the stall and maintains the idle, seems to indicate that the trigger for the stumble andeventual stall is a significant reduction in air, which points to thecarburetor.Someone previously suggestedthat I check the operation of the vacuum advance unit after warm up (I haven’t donethat yet); but if the unit is causing a loss of advance after warm up, I don’tsee why adding air to the system would offset that.Imay be a candidate for an A/F ratio kit.

[Steve D.]

Re: 63 _ Engine dies at idle after warm up

I double checked that to make sure it was oriented correctly.