My newly built 1340 motor continues to run for a few seconds after ignition cut off. I always thought this was caused by excessive carbon build-up in the combustion chambers or piston tops which when hot act like little glow plugs!

Any ideas?

too high compression for low grade of fuel, timing?

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The bitterness of poor quality (or Crappy Workmanship) remains LONG AFTER the Sweet Taste of Low Price is forgotten.

I'm using BP Ultimate 98 RON fuel and timing should be good, I'll look at compression in the morrow.

Cheers

What spark plugs are you running ??, I have the gear to cc a head if you need a hand.

I would re check timing and even advance a couple of degrees to see if it makes a difference.

My guess is that your carb mixture is to rich, what carb are you running.

Mal

Cheers Mal,

My plugs are NGK BP5ES and look a tad lean if anything (the tips are black and the ground electrodes are white)! The carbs are twin 1 1/4 SU's

I have a compression tester so I check that and post results tomorrow.

Not that kind of compression. Would involve removing head!

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1963 Morris 850 Smoke Grey
1963 Morris 850 Shadow Blue
1965 Morris Mini Smooth Van
1966 Morris Mini Van
1969 Morris Mini Deluxe Resto
5/72 Clubman Gt

Oh bugger! Sorry, I'm still learning

Mal, the offer to give me a hand? Where abouts are you? When are you free?

Marty , I will send you a PM

On a well modified 1275 running 98 it's pretty normal, IMO. With an iron head, anyway. If it doesn't do it, your C/R is too low.
I doubt it's the plugs, you could try colder ones but they are more likely to foul in traffic.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

drop your idle down a tad

&/or

retard your ignition a little bit

both of these will help reduce the chances of "run-on"

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No offence intended here but--> anyone writing a book about minis 30 years ago may not have experienced such worn or stuffed-with components as we are finding these days.

You should put your heart & soul into everything you do.

How does retarding ignition help, there is no spark when you've turned it off!
It's either hot spots in the head, or red hot plugs...

Mine does it when hot, even though the head is bathtubbed and has no beak.
I just let the clutch up with the footbrake on, I've done it for years.

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

I am guessing if timing is to far advanced you will not burn all the fuel in the chamber, hot spot or very high CR would ignite it once ignition is turned off ?

If compression is too high is it possible to reduce it?

More dish in your pistons, or get your head worked to increase the chamber size

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Marty, that will mean head off and possible engine strip, do you have any details of pistons and or head work ?

M