Buy a 5 gallon can of 100+ octane unleaded race gas and see if it runs on. My opinion is it's low octane gas and not ignition timing, unless the timing is WAY too advanced and the the engine is getting ready to melt the pistons then it's the gas not the timing. I run a mix of VP 100+ octane fuel R+M/2 with 93 pump R+M/2 and my car never runs on or knocks. 1293 A+ 10.5-1 CR, HIF6 (would need to look at my notes for the needle),  LCB w/RC40, 5degrees advance @idle w/no vacuum.

I get why Jemal says to clutch/brake it to make it quit but I just prefer not to.

That is why i said presumably in my second post Jemal. If he only has 25 degrees total advance i would think his timing may be retarded at idle or his distributor is not up to snuff but without knowing what he has engine wise it is hard to tell.

Kent did not say he had 25 degrees at idle!  The engine would not start or "scream" with the timing off by that much, and I have previously spoken to Kent about the total timing being about 29 degrees. His familiarity with Porsche engines and setting timing makes me comfortable with his capabilities!

Just an FYI, most distributors set at about 5 degrees at idle with no vacuum will give just under 30 degrees total at 3-4000 RPM, and about 12 with vacuum hooked up.  A 1275 sounds "best" with about 12 degrees at idle, but that will almost always give well over 30 total with a mechanical distributor, and they just fight themselves because of the long stroke, loose power, and risk detonation.   A vacuum advance distributor works great on a street Mini engine.  The non vacuum units require the timing be set to where they don't sound as good at idle! 

Get the idle below 1000rpm if you can. Also it helps a bit to let the motor idle for awhile after a run.

As Jemal says, run-on is not unusual these days, for the reasons he gives. Part of the problem might be incorrect fuel mixture at all engine speeds and loads, resulting in some carbon build-up. I have an as-built Metro 1275 with 123 electronic ignition, that runs like a top, but occasionally runs on. I know my mixture isn't perfect, but I can't afford a selection of needles or a rolling-road session - I run what I have.

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Dan, i understand all that but most people give their timing setting with the vac disconnected not connected and that's why i was trying to establish why/what in my 2nd post. I don't know if kolsen has a stock engine or built one, if it is stock there should be no need to stall it to stop it imo.

Malsal: He could have a vacuum advance distributor. Timing is set to 8 degrees at idle with the vac. advance disconnected. Once satisfied, the tuner reconnects the vac. advance, which pushes it up off the scale and resets idle which also climbs. I'm not sure what the resulting total advance actually is, but could be around 25. I just know it goes out of sight on the toothed scale. One of those fancy digital timing lights (which I don't have) would give you the reading.

Really !!! Maybe you know more about the engine on this car than the owner has posted for me to know.
Just curious why is 25 degrees of timing at idle acceptable (presumably). Not wanting a back and forth shindig here Jemal just wondering why would you need that much advance and the "benefits" and how much is max advance when running 25 degrees at idle ?

Hi Kent!  Not at all unusual for a good running Mini engine to run on or 'diesel'   when shut off.   The ones that "really scream" are going to have relatively high compression, and the quality of fuel available is such that they will ignite the mixture from the heat and pressure of that compression. Just about ALL cars would still diesel if not for fuel injection, which stops the fuel when you turn off the ignition, unlike a carburetor which does not know any better! 

You have already found the best solution, one that I use all the time with my 13 to 1 engine... Simply get into the habit of putting the car in 1st gear and gently let out the clutch as you turn off the key.  Don't bother with any of the advice to set your timing or anything else... there is nothing 'wrong' that can be fixed, unless you want to rebuild the engine with 8 to 1 pistons and give up about 25% of your power!

The method I describe has the added benefit of randomizing where the engine actually stops.  It's a bit obscure for people to understand that the A-series engines stop in one of two orientations when shut off, so that your starter is always chewing on the same few teeth of your flywheel ring gear. Using the clutch to stop the engine spreads that wear over all 107 teeth (Pre-Vert0) or in your case all 129 teeth, so it really is a win-win with no down side!

25 degrees at idle ? That's a start you only need around 8 degrees at idle and 28 to 30 or so fully advanced. Is your idle set high ?

I got a new exhaust/intake gasket installed.  I thought I might have to add another small muffler but now it's much quieter.  Spend some time reading about SU carbs, haven't had one since my Triumph and MG days back in the 60's.  Did the tune up, mixtures and balance, yesterday and then a test run.  Phew ! she really screams now ! But when I got back home and turned her off I get that run on you need to put her in gear and let out the clutch to stop.  What's with that?  Fuel or ignition??  Timing is about  25 deg, so what causes that?