I suspect that in this case, you will not convince him that he has not found the all out cure for dieseling that applies to every car ever made.

Glad you found your problem, but:

You did not dispell any myths. Of the possible causes, you found the one that applied in your case. That does not prove the other possible causes wrong.

Not so crazy if your old one was not providing the correct advance rate, leaving you with an engine with improper combustion and carbon buildup which would glow (hot spots) and cause dieseling.

the way I got rid of my dieseling was swapping out my aldon full centrifugal advance distributor advance for one with a vacuum advance.  It sounds crazy but I haven't had a problem since.  Glad you found your problem and were able to fix it.

Sounds almost like you had a bent needle......

the reason why i revived this thread is because, i just want to share what i did to eliminate dieseling on my hot spanking mini.

as you all know, my mini has been dieseling months since i bought it. and from then on i have been looking for ways to eliminate it. This afternoon, i replace the carb needle for the first time , without replacing the carb jet.  and guess what, yes you are right, NO MORE DIESELING!!!! im so happy.  i tried turning engine on and off several times/ and driving it several miles then turn engine off, still NO DIESELING!

i therefore conclude:  Dieseling is mainly due to excessive fuel delivery./ worn out jet or needle causes carb to deliver gas when not needed.

MYTH associated with dieseling: : engine hot spots/ timing issue/ valve adjustment/running lean/  whatever,etc etc etc!!!

now who needs hif38? hehehe

The 850cc was advertised as 34 HP. 34HP of pure British steel. Have some respect.

Wrong again.

If the float valve is open, gravity will fill the bowl, and with the engine dieseling (or running), the bowl level will go down. On every SU carb I've seen, the fuel inlet connection is higher than the bridge and top of main jet. With a full tank, the gas will flow. The only thing stopping it is the inlet valve. In fact, if the inlet valve sticks open, fuel will continue to drain until the tank level drops below the carb bridge.

Back in the 50's we used water. It is somewhat effective. Techron is unbeatable.

Excellent points Paul, very helpful

1. High idle means the throttle is open too far thus allowing fuel to be drawn in after Ign is switched off and therefore lighting off in hot combustion chamber.

2. Retarded ign gives lower idle so idle screw is adjusted to compensate idle speed = throttle open too far causing same as #1

3. Lower octane fuel is more volatile than higher grades= easier to light off in hot combustion chamber

4. lean idle mixture causes combustion chamber to get hot at idle, also causes idle screw to be opened to compensate= 1 and 2

5.Overheated engine causes hot combustion chamber.

6. fuel float level too high causes fuel into intake manifold at low idle speeds, if it's a bit higher still it will stop dieseling due to quenching ie, too rich to light off.

As I said previously there are any number of things that will cause dieseling BUT if you check the basics FIRST it will probably go away! and the car will run better cleaner and milage will probably get better....................................................

I did the spray water bottle trick last week. But the plugs were still carbon-ish.  

Went through a whole squirt bottle, set the idle to 3000 and squirted till it was about to die.  Never did this trick before but am wondering if I should just sea foam it....?

I had a ton of carbon last time but have leaned it a little since, plugs are a nice brown but have too much burned toast as well.

My2c...

You have a 1950s design engine, with a cast iron head. Iron has poor heat transfer. IMO if it's idling @ 1100rpm+ like mine and doesn't ever `diesel', your C/R is too low.

Later A+ versions of this `tractor technology' engine had an air gulp valve on the intake manifold, specifically to prevent this. So Rover were aware of the problem.

I'm with Jemal here, just let the clutch up in gear when you shut it down. It don't hurt it.

I do have an electronic fuel pump.  I live in Michigan on the coast of Lake Michigan so not much above sea level. I have bought cheap low octane gas. I'm new to the mini game. I will try the more expensive gas and ear test the idle (even with my almost lack of hearing) and I will show up at events for more help. I'm excited to be a part of the mini family. Thanks for the advice chaps. 

Once again, step back and think.

Yes, there is a check valve. It keeps fuel from going back into the tank, but lets it flow towards the Carb or injectors if it wants to

The float valve in the carb keeps the bollw from overflowing, while freely letting in fuel if the level in the bowl drops (or if it sticks).

On a flat surface, it may or may not matter that the tank is mounted fairly high. It could pass through. but parked going downhill makes more of a difference, and many times is a problem.

It does not matter where the venturi is located as long as air is being sucked past it.

Therefore,

If the engine wants to run after the key is turned off becuase of hot spots, whether deposits or wrong plugs, as it runs it draws air and fuel into it, the bowl drains, and the fuel can continue to fill the bowl, although this total combination probably isn't very common.

I have seen tanks drain into the crankcase when floats stick open and cars are parked on sloped driveways. The fuel passes from the tank, through the pump, through the bowl, and into the cylinders. The next morning you have a whole lot more oil than the night before, but it smells of gas, and giving it the fuel dilution test (hold a match to the dipstick and see if it flares), you know for sure.

  Quote-->"If the tank is full when the carb bowl gets low, it's float valve will open,allowing fuel to flow under gravity"     so clearly, you meant IF THE TANK IS FULL, there is no need for any gas pump of any sort because gas is being supplied with the aide of GRAVITY???? hmmmm? and until the gas level goes down that's the time you have to turn on your electronic fuel pump because gravity is gone??? hmmm???

if the float bowl is above the venturi that's the only time gravity will apply.

if i apply Syllogism in the scenario that you just presented, this will definitely not stand in any court of law.

My goodness!  We can't really have Analysis without the arse now can we...
 

Only fuel injected cars will stop running when the eelctric fuel pump is switched off.It is entirely possible for a Mini with an electric fuel pump to continue dieseling after the ignition is switched off. ALL carburetors have a fuel bowl. The carb will continue to supply fuel mixture until the fuel bowl runs dry. In addition, the top of a saloon fuel tank is higher than the carb float valve. If the tank is full, when the carb bowl gets low, its float valve will open, allowing fuel to flow under gravity.

A Mini can also be driven (not necessarily dieseling) for several miles on not much more than vapours. I once accomplished about 3 miles on fumes after the tank ran dry late at night to find an open gas station. I had to push it up to the pumps though.

Apparently his 'double major" isn't in physics or engineering. "This is where the double major kicks in..." in the pants!