Dieseling

[tschmitt]

Want to get some feedback to see if my thinking on dieseling is correct. Since dieseling happens when the key is off, thus no fire/spark, it cannot be related to timing of a engine but really has to do with fuel getting into the combustion chambers and igniting. This can be in correlation to having a fuel leak in the carburetor (possible plugs leaking on a Quadrajet) or having the throttle plates too far open during idle thus exposing the transfer slots too much. Solution would be to work to get the transfer slots to an ideal range (0.035-0.040 for a Quadrajet?). This can be achieved by increasing the idle bypass air to allow the throttle plates to be closed further thus reducing the amount of transfer slots exposed. I am somewhere on the right track for providing a solution to dieseling when using a Quadrajet?

[Kenth]

Bottom plugs leaking is a 1968 and earlier "feature". 1969-on this issue was cured by Rochester/Carter.

But the cause of dieseling or run-on at shut-off is more of a too much opened throttle blades causing "nozzle drip".
The remedy for this can be more idle bypass air in conjunction with larger idle tube restrictions.

But, i have found that more often than not the remedy is using ignition vacuum advance at idle speed.
This will by itself locate the throttle blades in a lower position.
It was not for nothing manufacturers started using "anti-dieseling" solenoids when they started using retarded ignition (ported source) at idle speeds to lower certain emissions by heating the cylinder heads with help from the retarded ignition.

[tschmitt]

Bottom plugs leaking is a 1968 and earlier "feature". 1969-on this issue was cured by Rochester/Carter.

But the cause of dieseling or run-on at shut-off is more of a too much opened throttle blades causing "nozzle drip".
The remedy for this can be more idle bypass air in conjunction with larger idle tube restrictions.

But, i have found that more often than not the remedy is using ignition vacuum advance at idle speed.
This will by itself locate the throttle blades in a lower position.
It was not for nothing manufacturers started using "anti-dieseling" solenoids when they started using retarded ignition (ported source) at idle speeds to lower certain emissions by heating the cylinder heads with help from the retarded ignition.

That's interesting. I have just recently learned about the idle stop solenoids used back then and how they work.

[77cruiser]

If you can increase the timing &t. close the throttle plates a bit.

[quadrajam]

A tight quench distance helps a lot too.

QJ