We got two loads of bad fuel in Montana...once back in B.C. and filling up at an ESSO problems were gone...in the mean time, I had replaced the dizzy cap, rotor and spark plugs, even bought new ignition wire set (not installed).  Mini has an electronic pack in the dizzy (no points/condenser).

This may sound idiotic but I had a similar effect after filling up at the "cheap" gas station in town. My car sputtered and ran rough too. This is with 2 fuel filters. I have not filled up there again and only get Chevron Mid Grade now. I haven't had that problem again.

Maybe bad gas is your culprit.

In another life I work on SAABs. On a 900se turbo I went through the complete fuel system including replacing the fuel pump in the tank and any thing else suspect, to no avail. The car would do as you describe, acting up with a full tank of gas. I finally drilled a hole in the gas cap and this fix the problem.  I know this is not practical on our mini's so I would insure the venting system was in good order. Some times the simple things bite us.

fuel pump is inside the tank. The sock style filter gets clogged pretty easily. Wait until your almost empty and go ahead and pull the tank and clean it out. I'd be willing to bet you have sllt in your tank. It came/comes from empty tanks sitting without fuel in them for a period of time and condensation forms inside the tank and rust forms and settles into the tank like a fine silt. gets sucked up by that intank pump and takes out your pump. Seen it a couple of times. Enought to convince me it's not uncommon.

The other cause, and the most likely is a vacuum leak at the front of the car. There are some elbows on the SPI that crack and leak. Do a search and you'll find lots of stuff on that.

Should clarify that the car is an SPI...

Here is the symptom in detail for kicks: I am at a stop light... car is idling perfectly... revs perfectly.... green light.... let out the clutch... push on accelerator... car advances forward... chokes... moves forward... chokes... stalls... restart...moves forward... hestitates and sputters as I floor it to get through the light that is now amber and four cars are honking at me... drive with pedal floored out of frustration as car bucks like a young bronco...park car.... curse at it as I storm to my front door... morning... car starts... bucks once and continues on as  though nothing happenede the day before.. notice my once full gas tank now reads 3/4 full.

Whatever you do, don't add any fuel additives to your Mini's gas tank. Mini's don't like most additives! Your plugs will foul. Like the guy says on the Men's Suit commercials, "I guarantee it!" Hope this helps.                   Mini Estate

I know you say it sputters on acceleration only when the tank is full .

but...do the simple stuff first..make sure the carb oil is topped off - without it, sputtering on acceleration happens, especially on quick jabs of throttle

I just replaced the vent tube on the top of my gas tank (the gas cap itself is not vented).  An easy job.

Mine was split, could yours be plugged up with dirt or insect stuff? (about 3 feet long or so, it vents out the bottom of the car through a hole in the boot) 

I just used vacuum hose from Advance Auto (does not need to be special hose as it is not pressurized fuel, just vapor.)

When you fill up, are you stirring up debris in the bottom of the tank? I know you said you changed the filter, but what about water? One of the first things I did when I bought my mini was to put a hose down into the tank and suction out a cup of fuel to see what it looked like. Was ok, but I also installed ( in the engine compartment) an inline filter of clear plastic so I could see if water was accumulating. I installed it sideways, not vertically, so water would settle, get trapped ,and be visible.

if not these two items, then it sounds like more detective work. Who knows, the fillup might be coincidental. 

So... this happened again... and in rush hour traffic... long day etc... it is very frustrating.

I am certainly not trying to overfill. I assume when the lever stops and gas stops... its at capacity. Gas never comes shooting out of the tank. Is there something that has gone awry further to what has been said?

Other than my mini... I am a huge vw nerd. In the MK1 rabbits... you knew your feed tube was deteriorating if you took a hard right and the car sputtered...

Is something not functioning properly... like a gas cap etc?

I'd go with Spitz on this you probably aren't venting and it's locking up. Easy fix don't put so much gas in. I never completely fill if I do I end up with gas spilling down from the filler. Esmith had a post on the splash guard.

No doubt KY jelly works for that slam bam

Not to quibble, but it seems to me that the word "phallic" was used correctly.  Not only did Harvey use the word correctly, but dispensed a rather humorous dose of innuendo in the process.  (HAHAHAHAHAHHA)

Proper grammar and spelling does matter, always, as does proper speech.  The ability to communicate clearly enables the reader or listener to assume that you're somewhat intelligent.  In fact, the root of the word intelligible is 'intellig', the power to know and think.  Therefore, I normally avoid using spasmatic idioms in my text and speech.  I've found that effective communicators typically take pride in their work and work to a higher standard.

Some might consider me to be a bit loquacious, but I consider myself to be rather eloquent and generally capable of accurately communicating issues and solutions as required. 

lol, you used the phallic word in a wrong sentence, lol.

i toldya guys, grammar is not an issue in any forum.. lol

ill get back to you, i am just busy replacing the rubber boot on my steering system.. this wont take long.. 

Perhaps it's overfilled and fuel has got down the venting tube...if the tank can't vent, the fuel wont want to travel

The fake Robster strikes again. Where do you insert that phallic Gumout jar?

not the ultimate solution, but it can help clean you fuel system.. i use this once a month.

Did you check that the float bowl and needle valve are clean and that the ventilation tube on the top of the fuel tank isn't blocked or kinked?

It could very well be that a bit o'crud became dislodged when you changed the fuel filter and is blocking the outlet from the float chamber.

I have noticed as of late... that when I fuel up the mini... it will start to sputter when accelerating... it feels like the car is literally starved of fuel and then fires back up again. I have checked multiple times whether or not the coil wire or spark plug wires have jostled loose but they seem fine.

I replaced the fuel filter about a month ago, everything else is maintained on schedule.

cheers

parker