I'll answer one of your questoins.
"...question: does any one of you experience "dieseling" using electronic fuel pump???????  speak up! i bet none!!!  cuz as you turn off the key, gas delivery gets shut off right away.!!!!  ( see the logic now? this is where the double major kicks in..."

When I first had my '59 Frankien-Mini with a 1380 & electric fuel pump, it would diesel.
Sorting out the cooling and switching to a higher octane made it go away. Your experience may vary as any number of things will cause dieseling.
I will not address your other rantings that you call "independent Analysis." [rolleyes]

Plain and simple,, if we use our common sense "dieseling" is caused by:

1) a spark(fire)

2) gas

3) air

now, a normal operating car SHOULD Kill ALL three components as soon as the KEY is turned to OFF position. 

now tell me how can a high grade fuel cause this phenomenon?????? how????

potential cause why these three components continue after car is turned OFF:

1) spark--- red hot spark plug tip/ caused by too much air vs. gas (scientific name: "lean mixture")

2)gas----excess gas delivery is caused by worn jet and needle/  too wide play allowing excess gas to squirt and enters the combustion chamber and ignited by the red hot plug tip which then turns over the engine, triggering the mechanical gas pump which then pushed gas to the carb bath and onto the WORN OUT needle and jet., and since the venturi butterfly is not totally closed, ample amount of gas will enter through.

question: does any one of you experience "dieseling" using electronic fuel pump???????  speak up! i bet none!!!  cuz as you turn off the key, gas delivery gets shut off right away.!!!!  ( see the logic now? this is where the double major kicks in)

3)Air----air simply gets sucked as the engine turns over.,,, no biggie!

waiver: this is not a theory, this is simply an independent Analysis.

What I posted is based on how I learned to tune up cars in the 50's by a Hungarian refugee, using matchbook covers to adjust points. I bought a timing light a few years ago and tested it on my perfectly running Corvair with the engine I had just rebuilt from scratch. The light said it was way off. Haven't used the light since.

Yeah, that "original spec" thing. Unfortunately like value depreciation, the "spec' deteriorates as soon as one drives it off the lot. Ignition points wear, spark plugs wear, oil gets dirty, air cleaners collect dirt and change efficiency, deposits build up in the combustion chamber... "spec' becomes a bit of a moving target.  Then someone tunes it up and it may be beter or not so good.

Richard's description eariler in this thread on how to tune by actually "listening" to what the engine tells you depending on its condition and the environment you're driving in, is actually "old school" as in before analysers, timing lights, dwell meters etc.  - pretty much like when the Mini engine was first developed. Still pretty good advice - if you know how. Interesting side-point: the 123 elctronic ignition system has an assortment of suggestions of which curve to select, based on engine spec, but Marcel Chichak (who was involved in its application to the Mini) says "your engine will tell you what it wants".

True Alex but remember Poison has a Mini "Special" with what he thinks is a 1098 engine in it but we all know better than that. I can't remember or be bothered to look at an old post to see if it was a later model A + or not. The 87 over here in Florida is garbage from most places and all my Mini's run better on the higher octane fuel except the daily drivers with a/c they seem to run fine on 87.

I'd hazard a guess that all 850s, and 998s built up to 1980ish will run quite happily on 87 PROVIDING that they are unmolested and are original spec. Malsal will remember our old 2* and 3* petrol; exactly the low octane stuff they were designed to run on. Once the A+ arrived with much higher compressions, then 4* or 89 would be needed.

Fill up with the best fuel available. The few cents extra per gallon is tiny compared the costs of an engine rebuild...

Octane is a valid point. The Haynes manual says 95 RON. That equates to 89 on the US scale, so at sea level 89 should be right. Go up into the mountains and 87 would work fine.

That is why I said once everything was cleaned up, "put in the gasoline you will use" and set your timing accordingly for your fuel and your altitude. Unfortunately I will have to use 85 RON rather than 95, as it is the only octane offered in Tarija. Once I bring it to Santa Cruz I can splurge on 90 RON, although it costs 34% more than 85 at the few stations that carry it, and is not always available.

ONE MORE note. I just noticed one of the posters said "clean your filter". That is the WORST thing you can do for your engine. Filters are not designed to be "cleaned" and any cleaning other than a vacuum cleaner will damage the fiber structure and let dirt through. Any dust on the surface is actually helping the efficiency of the filter, as fine dust is attracted to it and this increases the surface area. And just opening it to handle it breaks the seal, which frequently will not completely re-seal do to previous compression. Air filters are among the least understood concepts on cars.

Well if you had read the Haynes manual you would know that 87 octane is not good enough for a Mini, it will run on 87 just not it's best so break out the wallet and cough up the extra cash you make with that double major put some 93 in it pass on the snake oil additives and feel the difference. BTW just so we can get this JEG bent jet issue out of the way i can send you a bent jet caused by a broken stabilizer bar mount just give me your address in Yuma, Killeen, or the rock in the desert you live under or wherever else you may say you live and i will send it on.

To the poster: Dieseling is caused by any number of things including grade of fuel, timing, high idle, carbon deposits to name a few each car can diesel for a different reason. As previously posted you need to get the rest of the car tuned up to specs before messing with the carb adjustments.

Quote:

Originally Posted by Alex

lol, i heard that you are the Editor in chief and contributor of the minimagazine, i have formulated an ideal Oil additive mixture for the minis on the other thread, i will allow you to post them on the minimag so the magazine will get more sales. 

my offer is not forever, so take advantage of it.

nice to know i have an avid fan in UK...lol

when i first bought my mini, it was running fine,until i fiddle with the carb, since it was my very first time to deal with Jurassic SU carb, i didnt even know where the screw is to lean and rich the mixture, then i finally found it just beneath the jet. i screw it up and down, somehow i upset the tunning so it became lean, from then on i've been experiencing this stupet run on thang!!! AND i have been using 87 octane all along.

then my car judders and caused the needle to bend...and the rest is history!

Run-on or "dieseling" in a gasoline powered engine has nothing to do with timing. The ignition is off when the engine runs on, there is no more spark. Jemal is correct try higher octane fuel. My car "diesels" on 93 octane pump gas but not 100 octane VP unleaded race gas. No changes in timing. Carbon deposits can cause it, poor cooling can cause it, and cheap gas can cause it.

To any newbies, ignore the rantings of our village idiot. (Boison)
"...i have used tons of liters of engine cleaners mixed with gas, name it. Actually,when you peep through the spark plug hole on my mini, you will see that inside of my combustion chamber is super clean, but the car is still dieseling..."

So far, Dr. Poison has tried all sorts of witch's brews. Claims to be able to see the combustion chamber is clean.(I'm wondering how he can see the top of the combustion chamber in the head as I have not heard him brag about a boroscope.)
So, how is he going to cure his dieseling problem? Dump some more stuff in the fuel tank. (shakes head)

BTW Dr. it's spelled "Kerosene" 

Wow for a simple question you seem to have got a lot of complicated answers!! I forgot about the 2nd part of your question. Yes high idle speed will make the problem much worse, unfortunatly giving a guide for idle speed is a bit iffy as it depends on state of tune and other variables but as a rule you want it as low as you can consistant with steady running at idle, you don't want it chugging or hunting all over the place or indeed stalling whenever you get to a light! The speed will depend on engine condition and state of tune hence my original post "Check the basics first" As a Rolls-Royce apprentice they beat that phrase into you...............................

Oh yes, the OGA...oronite gas additives, im all for it...hands down. i'll try that.

the only issue i have with these super duper carb cleaners is that they are harsh on non metal components of the carburetor like the need valve viton tip. they easily worn out and eventually even melt. causing overflow

To give you an idea without calling names, what I prepare according to Oronite (Chevron) is 6 times stronger than one of the leading US brands' "concentrate".

Some aren't much more then kerosene and alcohol.

yes Rick, i think i maybe wrong on that one, it's just based on my experience. i may very well be wrong., it's just that i already  used many kinds of fuel system cleaners and i still experience dieseling., we may ask other members who just rebuild their engines and already experience dieseling. if there are, please share your experience.

the most aggressive cleansing method that i did to my 80"s engine is to soak about 3-4 ml of kerosine(yes kerosine,don't panic) or seafoam overnight, two chambers at a time.. this totally eliminated and dissolved carbon and gunk build ups inside the chamber periphery and in between sticky pistons.

The hot spark plug tip is a valid point (change plugs) but your comment "the story about carbon build up igniting and producing heat is a myth." is way off base. They are very, very real (well, they don't really produce heat, they just store it). And there are a lot of useless cleaners on the market. I've studied the ingredients of most of them.

The carburator being worn or not does not significantly contribute, since an operating engine draws air through the carburator, where the jets add fuel as a venturi. As long as there is gas available in the bowl, the moving pistons will draw it out. And if the fuel pump is mechanical, it will keep on supplying the carb with fuel.

This is not like an injected engine where the injector cuts off the fuel if the power is cut.

ok, let me handle this, i have the same issue on my mini btw, as far as my analysis is concerned, the very main reason of dieseling is engine running too hot and  lean and also due to worn carb components, the tip of the spark plug becomes red hot due to extreme heat caused by lean mixture.,now as you turn the key to off position the worn out carb jet and needle continues to deliver gas to the chamber while the red hot plug tip is waiting inside the chamber ready to ignite the gas then combustion happens thus engine keeps running until that red hot plug tip diminish in 3-5 secs

 i have used tons of liters of engine cleaners mixed with gas, name it. Actually,when you peep through the spark plug hole on my mini, you will see that inside of my combustion chamber is super clean, but the car is still dieseling.

Pull your plugs, you'll notice that the tip is whitish in color,thats the sign that you are running lean.

things to do:

clean your air filter

determine if you need to replace your worn carb jet and needle, if so then replace them or better yet,rebuild the stupeyt carb.

use colortune to tune your carb (don't just guess).. This item is available for sale here in Minimania

check your engine oil level/ and coolant level, maintain it on full... low levels can contribute to the overall heat of the engine.

 as much as possible avoid high revs, a sweet 50mph cruise is just perfect., no rush, no pressure!

Maybe we should be clean on definitions. I understand your comment of "dieseling" to mean it continues to run without a spark. My answer above is based on that.

Some answers go directly at "pinging". "Pinging" will be caused by the same causes of "dieseling" plus timing too far advanced for the gasoline you have. Increasing the octane will alow you to run more advanced timing without pinging.

So once it is cleaned up, and you are sure the distributor is clean and does not have excessive bearing wear or point plate pivot wear, put in the gasoline you will use regularly, and set the timing, twisting the distributor slightly one way or another until you get the smoothest idle (probably not more than 1/2" either way since your engine already runs). Then retard it slightly by twisting it in the opposite direction of what would be pulled by your vacuum advance. Then drive it, trying to accelerate with a lower than normal rpm (when you know you should have shifted already). If it pings, retard it a little more. If it does not, you can advance it a bit (twisting in the direction of the vacuum advance). 

The perfect timing is determined this way. A timing light will give you a setting fairly close, depending on your location above sea level. With non electronic engines, I have to do this regularly, as one house is at 6000 ft and the other at 1200. I originally set up and tuned my Corvair at my office at 6600 ft, and it ran perfectly, but it pinged at my house at 6000, so had to retard it to avoid pinging on the way to work.

Back in the old days when I often worked at 15,000 ft above sea level, I'd stop at least twice on the way up from 6000 to advance the timing.

 EDIT: Yes, valve timing is fixed by the timing chain. Any variations would be caused by a worn chain or chain tensioner. You would probably hear it rattling. Yours may be double or single, depending on the year and whether or not someone changed it out from single to double as I did.