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Re: octane and timing

Subject: Re: octane and timing
From: David Littlefield <>
Date: Mon, 23 Jul 2001 10:50:44 -0500
On Mon, 23 Jul 2001 08:41:48 -0400 "Gordie Bird" <>
> In a effort to cure the run on in my 1622cc MGA I put a tank of 110 
> octane
> racing fuel in.  It cured the run on, but now I have trouble 
> maintaining a
> steady idle, sometimes even stalling when coming to a stop.  Prior 
> to this
> tank of gas I had a nice steady 800 - 900 rpm idle.
> So, most learned listers, will altering the timing help this 
> situation?
> Safety Fast!
> Gordie Bird

Maybe, but do you intend to run 110 octane all the time?  A street motor
(relatively low compression) will not be able to combust that high an
octane fuel with much success, hence your idle problems.  Also, if your
car sits around much that 110 octane will deteriorate very quickly, much
more quickly than pump gas.

You may decide those trade-offs are not worth just trying to stop some
run-on.  My 1622 ran-on as well, and I just got in the habit of bumping
it in second gear to stop it.  The MGA's head has a widow's peak in the
combustion chamber that tends to get hot and cause run-on.  The next time
I have it worked on, I'm going to have that shaved off.

If you insist on using a higher octane fuel, use the lowest one that will
still cure the run-on.  I don't use anything higher than 104 on the
racetrack in my Midget, and the local Spridget guru tells me I am wasting
my money.  He says that 93 octane pump gas is fine for the relatively low
compression motor I'm running.

David Littlefield
'62 MGA MkII
'51 MGTD
'74 MG Midget vintage racer
'88 Jaguar XJ-S

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