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Dieseling is a result of excessive cylinder head temperatures. The exhaust valves may be running hot and when you shut the engine down they act like glow plugs. Running too lean is the usual cause and that can be fixed with some carb tuning. Since it sounds like this problem arose after going back to a mechanical pump, I'd suggest that your float level has dropped due to lower fuel pressure. Reading your spark plugs will tell you quite a bit and I suggest doing that first. If you see grey or white on the plug instead of a tan/orange your engine is running too lean. If they are tan to dark brown, I suggest you read further.
Sometimes it's carbon buildup in the chambers that's the culprit. This is often caused by ring or valve guide oil leakage into the chambers. This can sometimes be corrected by using the Water Injection Cleaning Method.
For a short period of time, pouring a small but steady stream of water into the carb while running the engine at 2500 RPM will increase the cylinder pressures significantly and often breaks carbon deposits loose. You don't drown the engine, but as you pour out a 12-16 ounce bottle, the RPM should drop about 500 or so. The duration of the pour should be short. There is a risk of damage to the rings and valves if you pour too much water too fast so you have to find the balance between pour rate and duration. Listen to the engine as it will tell you when you are pouring too much too fast as it will begin to shudder.
1977 Cherokee Chief - The Blair Jeep Project III
A collection of parts flying in close formation
Pulled a plug. No dark coloring and no white. Just a small area of orange/light tan. I backed the idle off a bit more and drove it just now. After setting timing with a vac gauge, the engine was nice and warm. 3 shut downs with no dieseling. Hope to be good to go. Thanks all
84 Grand Waggy-Radio Flyer (Garnet Red/3M Ebony Metallic woodgrain, with honey interior) AMC 360 2004 4.8LS/Advance Adapter/727/242 D44/AMC20 Serehill tailgate and headlight harnesses Ongoing thread-viewtopic.php?t=11897
If idle mixture isn't correct your idle screw will have to be too far open and will cause dieseling. Not enough base timing can cause too. Throttle plates shouldn't be very far open at all. Causes carb to run off of main circuit instead of idle circuit. If you're on a higher altitude youll need 15degrees base timing.