Overrun

[harrymini]

Just getting the final bits done on the historic lookalike, when I have been out in it and turn the engine off I get overrun/ dieseling. Is there a fix to stop this or something I have to get use to? It has just been tuned on a rolling road, is there something they could have done to prevent this?

Cheers

[Catmint]

I have fitted the anti overrun selonoid valve from a metro before when I had this problem, that goes to the inlet manifold. Turn the engine off and it opens letting a load of air into the engine

[111Robin]

I generally just blip the throttle and as the revs drop off below idle speed (before rising back up) turn off the ignition. Seems to work but not necessarily on every car.

[Peter Laidler]

I haven't got the answer as I haven't got the car in front of me so I'd be guessing. But fitting an overrun valve or blipping the throttle are palliatives and not cures. Surely the answer is to find the fault - excess fueling - and cure that somehow.

Later MGB's had an overrun or a gulp valve(?) fitted to cure a carb problem but this was easily sorted out

[surfblue63]

Try fitting a cooler running spark plug.

[Andrew1967]

HOY did that so Dad suggested ignition may be a bit retarded (set up static). Turned distributor gnats cock to advance and it’s cured it.

I did have to re-fit the anti-run on valve to an MG Metro engine I fitted in a Mini years ago, as that was the only way to stop it running on.

[nick@dunsdale]

agree with Peter no point in a palliative action

Would be looking for the cause most likely culprits incorrect ignition timing or incorrect carb mixture
Mini's only run on when something isnt right
Cant comment on newer emission equiped mini's though

[nick@dunsdale]

HOY did that so Dad suggested ignition may be a bit retarded (set up static). Turned distributor gnats cock to advance and it’s cured it.

I did have to re-fit the anti-run on valve to an MG Metro engine I fitted in a Mini years ago, as that was the only way to stop it running on.

To far advanced genrally cause's a run on or a weak mixture.

Thats what i was taught many years ago

I may have forgotten though as it has been many years since i made a living from engines

[Andrew1967]

I may have got it wrong Nick

I turned distributor very slightly clockwise ….

[nick@dunsdale]

I may have got it wrong Nick

I turned distributor very slightly clockwise ….

If your plugs are healthy colour not running to lean
Try retarding it you may be able to do away with metro anti run valve thing

[indigo]

What compression ratio does the engine have, as you may get overrun if the compression ratio is too high for the fuel octane rating.

[Dr S]

I used to get it after a hard run in Redshed. I’d let it idle and if needs be stall it on the clutch.

[iain1967s]

MG Metro needed the anti run-on aka decompression valve because of the heinously aggressive vacuum advance, caused by taking it directly off the manifold instead of from behind the carb butterfly. Keith Calver wrote an article about it a few years ago.

https://www.calverst.com/technical-info ... e-take-off

[nick@dunsdale]

MG Metro needed the anti run-on aka decompression valve because of the heinously aggressive vacuum advance, caused by taking it directly off the manifold instead of from behind the carb butterfly. Keith Calver wrote an article about it a few years ago.

https://www.calverst.com/technical-info ... e-take-off

Interesting article how a small thing like moving take off make such a dramatic difference.

[Andrew1967]

I may have got it wrong Nick

I turned distributor very slightly clockwise ….

If your plugs are healthy colour not running to lean
Try retarding it you may be able to do away with metro anti run valve thing

I will check plug colour to see how HOY is running but the anti run on valve was on a Mini long since gone.

[Daz1968]

I had it on my mk2 but as above a small alteration in ignition timing stopped it and also made it run cooler,
Pretty sure I had timing to retarded, I also use Bp7es plugs compression is 9.8:1

[mab01uk]

MG Metro needed the anti run-on aka decompression valve because of the heinously aggressive vacuum advance, caused by taking it directly off the manifold instead of from behind the carb butterfly. Keith Calver wrote an article about it a few years ago.

https://www.calverst.com/technical-info ... e-take-off

The 1990-91 Carb Rover Coopers also had the Metro type anti run-on valve bolted to the Servo support bracket.
https://www.somerfordmini.co.uk/catalog ... 774_100818

[Catmint]

The car I had it on was in the early 90's, and probably everything that we know is wrong now I did to it Those were the days