I have searched through the forum to find information on potential causes dieseling, and I am still a little unsure what is really going to solve this.
I am running a 38/38 DGES, Bosch blue coil (no ballast resistor), Pertronix, NGK BPR6ES plugs, distributor with vacuum module, timing was set to 25 degrees advance at 2700 RPM (per underhod sticker) with the vacuum line disconnected and plugged, and 91 octane Chevron gas.
The car used to always diesel when I shut it off, and I attributed this to the carb not having an idle shut off solenoid + "some other issue"
I just did a fresh rebuild, and the only things that have changed are a 292 cam, 9.5:1 pistons, 0.040 overbore. With the timing set statically at the first mark before TDC I did the 20 min. 2000 RPM cam break in run, and upon shutting down I got the old familiar dieseling.
So we have Fuel+Air+Ignition happening when the key is shut off. Fuel and air are coming from the carb, so the question becomes, where is the ignition coming from? Hot plugs? Fuel combusting under compression? I believe I have the right heat range plugs and sufficient fuel octane.
Many of the posts I have read point at timing as the major culprit - but what I don't understand is how this effects things once the ignition is cut off? Can anyone explain?
I found one post pointing at Chevron gas - any validity to this?
I thought about the option of an idle shut off solenoid, but then I am not sure if the 38/38 can run them and if this would just be masking some other issue?
I also got some advise to lower the idle speed, and perhaps even the floats in the carb. I still need to do a once over on everything, set the timing while the car is running, and readjust the idle speed before I take the new engine out for its first drive. I just have a bad feeling that this is still going to be an issue. I could always just keep letting the clutch out after I shut it off to prevent tohe engine from turning, but if there is some issue going on that can be fixed, I would prefer to fix it.
Brian
'72 2002