The engine dieseling (or running-on) when shut off is an indication of carbon buildup in the cylinders. That is a result of poor combustion, either from bad timing or mixture or both. It can also cause pinging. While the engine is running, the carbon buildup gets hot enough to act like a glow-plug and ignite mixture without the aid of a spark plug.  Once you get the engine running smoothly try to de-carbon the combustion chambers. there are an assortment of products and methods.

Old school: Depending on your distributor or electronic ignition system, initial timing should be set with vacuum advance disconnected (if you have it). With the vacuum advance reconnected, it should only be operational on idle/fast idle and be off when the throttle is open. Initial timing is set at a specified rpm. Mechanical advance increases with rpm to a specified maximum.
Your initial timing at idle should be somewhere in the range 8 to 12 BTDC (no vac advance), which should be the same as static timing (engine off). Mechanical advance (depending on the dizzy) should add advance proportionally for a combined total at around 5000 rpm of 28 deg to maybe 34 deg.

Generally speaking, set your timing to 28 degrees max advance without any vacuum advance hooked up. You'll need a timing light with adjustable dial or to mark your flywheel for 28 degrees so it light lights up in your timing hole at about 3500rpm.

for fueling, buy yourself a wideband air / fuel gauge, weld a bung in your exhaust or just stick it in the tailpipe (if you have no exhaust leaks) and set it with that.

If you want to pay someone else to do it for you, take it to Sonoma Raceway and Joe Huffaker's shop
https://www.facebook.com/huffakereng/

1380 built motor that has a couple of issues that I need help figuring out.

1 timing all the advanced lots of fuel and it screams but fuel smell all over the place.
2 lean it out to stop dumping so much fuel and it pings really bad
3 retard timing and fuel smell goes away and so does the pinging but the car diesel's when shut of . With this setting also very little low end and not nearly as powerful.

Anyone local who can help with a good carb/timing tune?