When the ignition is off but the engine is still spinning it is sucking in
exactly the same fuel/air mixture as it was before. If conditions inside
the combustion chamber allow i.e. glowing carbon or shards of metal, this
mixture will continue to be ignited, albeit irregularly giving the typical
shuddering, until the incoming mixture has cooled the combustion chamber
sufficiently. Tming affects Dieseing because it affect running
temperature - either too retarded or too advanced will cause higher
temperatures inside the combustion chamber. Hence timing affects Dieseling.
PaulH.
http://freespace.virgin.net/paul.hunt1/
(or if that URL doesn't work try )
(http://194.168.54.52/paul.hunt1)
-----Original Message-----
From: Chris Velardi <tchris@freewwweb.com>
To: Hans Duinhoven <H.Duinhoven@simac.nl>; tab julius <tab@penworks.com>;
steve conley <swconley@foxinternet.net>
Cc: Skye Poier <skye@ffwd.com>; MG LIST <mgs@autox.team.net>
Date: 10 November 1999 14:06
Subject: Re: What causes "shutoff shudder"?
>I believe it is due to un-burnt fuel in the combustion chamber, or un-burnt
>fuel exiting the combustion chamber in to the exhaust manifold or headers
>and combusting due to excessive heat. But I'm not exactly sure why it
>happens . It used to happen on my '61 A until I retarded the timing. The
>only way I could shut it off with out the damaging dieseling (engine
>actually running backwards) was to put it in first and drop the clutch and
>shut the key off at the same time.
>Chris "V"
>http://www.xtremedefender.com
>http://www.extremeforce.com
>
>----------
>>From: Hans Duinhoven <H.Duinhoven@Simac.nl>
>>To: "'Chris Velardi'" <tchris@freewwweb.com>, Tab Julius
><tab@penworks.com>, Steve Conley <swconley@foxinternet.net>
>>Cc: Skye Poier <skye@ffwd.com>, MG LIST <mgs@autox.team.net>
>>Subject: RE: What causes "shutoff shudder"?
>>Date: Wed, Nov 10, 1999, 8:56 AM
>>
>
>>I have heard this more, but don't understand.
>>At time you switch off the ignition, there are no sparks at the spark plug
>>anymore. Still the engine goes on (like a diesel engine).
>>Why should the cause of this be found in the incorect timing?
>>
>>Cheers,
>>
>>Hans
>>
>>'71 BGT which does not suffer of dieseling
>>
>>> -----Original Message-----
>>> From: Chris Velardi [SMTP:tchris@freewwweb.com]
>>> Sent: Wednesday, November 10, 1999 2:52 PM
>>> To: Tab Julius; Steve Conley
>>> Cc: Skye Poier; MG LIST
>>> Subject: Re: What causes "shutoff shudder"?
>>>
>>> Dieseling is most commonly caused by incorrect timing
>>> Chris "V"
>>> http://www.xtremedefender.com
>>> http://www.extremeforce.com
>>>
>>> ----------
>>> >From: Tab Julius <tab@penworks.com>
>>> >To: "Steve Conley" <swconley@foxinternet.net>
>>> >Cc: "Skye Poier" <skye@ffwd.com>, "MG LIST" <mgs@autox.team.net>
>>> >Subject: RE: What causes "shutoff shudder"?
>>> >Date: Wed, Nov 10, 1999, 8:25 AM
>>> >
>>>
>>> >
>>> >Thanks to all - I've had a number of suggestions, a few have narrowed
>>> down
>>> >to this valve, which I will check, but all are good ideas.
>>> >
>>> >- Tab
>>> >
>>> >
>>> >At 10:37 PM 11/9/99 -0800, Steve Conley wrote:
>>> >>The '73-80 models of B have the anti-run on valve. When you (not you
>>> Skye!)
>>> >>turn off the engine, you should hear an audible click from the valve
>>> >>kicking-in. It is located on the passenger side of engine compartment
by
>>> the
>>> >>carbon cannister. My '76 had a short period where it would diesel a
bit
>>> and
>>> >>it went away as quickly and mysteriously as it appeared. I just
shrugged
>>> my
>>> >>shoulders and didn't try to figure it out!
>>> >>
>>> >> Giving money and power to government is like giving whiskey and car
>>> keys
>>> >>to teenage boys. -(PJ O'Rourke)
>>> >>
>>> >>Steve Conley
>>> >>Marysville, WA USA
>>> >>'76 MGB Roadster
>>> >>GHN5UG393585G
>>> >>mailto:swconley@foxinternet.net
>>> >>MGB Online = http://web3.foxinternet.net/swconley
>>> >>
>>> >>
>>> >>
>>> >>-----Original Message-----
>>> >>From: owner-mgs@autox.team.net [mailto:owner-mgs@autox.team.net]On
>>> >>Behalf Of Skye Poier
>>> >>Sent: Tuesday, November 09, 1999 1:41 PM
>>> >>To: Tab Julius
>>> >>Cc: MG Nuts
>>> >>Subject: Re: What causes "shutoff shudder"?
>>> >>
>>> >>
>>> >>Word on the street is that Tab Julius said:
>>> >>> Turning off my ignition, my 78B's engine will often give me a few
>>> shudders
>>> >>> before it decides to shut off for good. This is an effect I
remember
>>> >>> fondly from other older manual, probably non-fuel-injected cars
(most
>>> >>> notably my long-gone yellow 72 beetle). Releasing the clutch (to a
>>> gear)
>>> >>> causes it to shut off quicker (okay, stall).
>>> >>
>>> >>The common term for this is "deiseling" or "run-on". The engine is
hot
>>> >>enough
>>> >>to continue to ignite air/fuel even though there is no spark. I
>>> >>could be wrong, but I think your 78 should have an anti-runon valve..
>>> >>the gulp valve?.. I don't know a lot about the emissions systems on
>>> >>later cars.
>>> >>
>>> >>Skye
>>> >>
>>> >>--
>>> >>1966 MGB - GHN3L Safety Fast! __,__\__
>>> >>The MGB Experience http://www.mgb.bc.ca/ (_o____o_)
>>> >>
>>> >>
>>> >>
>>> >
>>
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