Sir dave and sir dan,, just to prove to you guys that i follow all uour advices, here i tossed my $40 timing gun in the garbage bin, since you said that its not needed and its useless.

Thanks to everyone for the advice. I will see what I can figure out. 
Have a great weekend everyone!
Michelle

I was having the same problem.  My carb wasn't tuned correctly (too rich).  Believe it or not, I learned how to tune my carb from watching Wheeler Dealers.  Mr China was working on a Volvo pv544 with duel SU's and did a great job of explaining how to tune the carb in a very simple way.  I found the video on Youtube, but that section was cut out.  Maybe someone in the forum has a link to a video they trust.
Hopefully I'm not being a troll, I'm just saying what worked for me. Good luck.

I've started here under a different name when you were still suckling your mommy's t*t.

TROLL

i wonder who this "saggy" guy is...he only has 16 posts and yet he acts like he owns the forum. seeesh!

Barabas !!

What Dan said.

TROLL

How hot  a head gasket can take??  if there are red hot thing inside the combustion chamber, the engine gasket shouldve been fried long time ago if that's the case. 

And also, you will experience misfire if there is spark other than the spark coming from the plug. 

"Dieseling" is the result of combustion chamber heat triggering combustion without ignition spark. The heat could be due to hot carbon buildup, incorrect mixture and/or timing causing a hot engine, or a high compression engine not being provided with a high enough octane fuel. 

You have a 1275 - is it a high compression engine?

My Mini used to do the same thing and an old timer showed me this trick.  It works.  As soon as you turn the engine off press the gas pedal to the floor.  The burst of fresh air makes the diesel stop.  

+1.
(Ignore the drivel from 'specialist'.)

The minis on the 1990's onwards has the Anti-run on feature, i wonder how it works, what does it do?we can probably simulate it and re-design to make it work on the older minis. I Wonder how that device look like???. Are these available online?  My mini runs on  like crazy too, i need this device.

There are several old threads on this topic, a few within the past year.

To paraphrase some of the contributing factors and fixes listed in those threads....
Decarbonize the head, run premium fuel, retard the ignition timing, run colder spark plugs, stomp the throttle wide open as you turn the key off, with the car in gear slip your foot off the clutch as you turn the key off.

You can spend a lot of time and effort trying to make the root cause of the problem go away.  Instead, I just anticipate my car's engine wants to run-on and stall the engine every time I turn the key off.

Run premium gas, check idle speed is not too high. 

The troll is back.........

The phenomenon is called "dieseling" , i call it a phenomenon because up to this very moment no one has ever discovered the real cause or causes of it, all were just speculations. The only time you can tell the definite cause is when you actually experience to be inside the combustion chamber and actually see it with your two eyes what's happening inside there,which to me is very impossible.,but for now, you will here people saying, oh it's caused by lean mixture, oh it's caused by carbon deposits, oh it's caused by bad ignition timing, oh you need to do valve adjustments blah blah blah...let's analyze, a run on is actually moving of pistons and crankshafts inside the engine, what causes that is burning of gas inside the comb chamber caused by gas and spark.  NOW, it's easier to think that gas can still be present even when you turn off the key, but what is impossible to happen is the spark after you turn off the engine,,,,big question,,,where is the spark coming from??? you think it's carbon build up?? nope, if the inside of the chamber becomes so hot to the point that it becomes red hot, ever wonder what will happen to the head gasket?? it will fry even in the first dieseling, so ,nope that's not it. i tell you the answer. ----> the spark is STILL coming from the spark plug,  why? how? remember that the spark plug gets it's energy from the coil, as soon as you turn the engine off, the coil still holds thousands and thousands of volts until it dimininish in few seconds. that few seconds after you turn the key to off, the coil still supplies little energy to the spark plug, NOT to all spark plugs though but just to one. depends if the rotor inside the distributor is pointing exactly towards the distributor cap terminal to attain continuity..if the rotor does not point to any of the four terminals, then there will be no dieseling, ever wonder why sometimes dieseling is on and off? sometimes the car diesels and sometime it doesn't? it's because the rotor sometimes is not pointing directly to any of the four terminals.  ...bottomline, the coil still holds power to supply energy to the spark plug to initiate the spark then quickly diminish after few seconds.. a coil can hold 40,000 to 60,000 volts depending on the brand and ohm rating.


Nobody has ever discovered this phenomenon, it's not even in the book. it takes an inquisitive intelligent mind to come up with these analyses (plural).

Ok sorry I have a 1960 Austin mini and we just put a newly rebuilt 1275 in it. 
I believe its dieseling. 

I don't know for sure of course but old British cars can do strange things.

My Mini keeps running if the headlights are on.. turns off if headlights are off, well except for dieseling, which it sometimes does if I do not let engine slow down before turning off.. letting engine slow down for a few seconds or so normally takes care of the dieseling problem on the car.