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Re: [Mgs] too rich or too lean?

To: MG List <>
Subject: Re: [Mgs] too rich or too lean?
From: Aaron Whiteman <>
Date: Mon, 26 Oct 2009 13:19:40 -0400 (EDT)
On Mon, 26 Oct 2009, Paul Hunt wrote:

> One white plug does indicate a leak to that cylinder somehow, although as 
> cylinders are paired that's not strictly logical, unless it is on the No.1 
> side of the gasket which would affect No.1 more.  However vacuum leaks 
> usually tend to be 'stable', not come and go like electrical problems.  The 
> HT tests are really only valid if you can reproduce the problem with a timing 
> light connected.  You say it only happens at speeds over 45, but engines are 
> usually rev affected not speed affected.  If it happens at 45 in top, how 
> about the same revs in 3rd?  And 45 in 3rd as opposed to 4th?

At this point, we are going by my 1 AM memories, so keep that in mind.

When it was happening, the one thing I noticed was that engaging or
disengaging the overdrive did not help.  The same thing would happen
with the OD on vs off.  I don't remember needing to change my foot
when switching the OD, so the throttle position would be the same.

Yesterday, when I drove to the grocery store, I was able to go about a
mile at a steady 35 in 3rd, which is IIRC close to the same revs as 60
in 4-OD, but quite possibly a different throttle position.  If it's
not raining when I get home from work tonight, I'll go for a test
drive and experiment.

Regarding the plugs, I can't remember, is it the outside or inside
plugs that tend to run richer in the pair?  My initial thoughts were
that I'd see a difference between 1 and 2 and a similar difference
between 4 and 3 due to airflow differences on the intake.  I didn't
think much of the white plug at the time, which is why I need to look
at it again more carefully.

I also am unsure as to how quickly plug deposits change.  After
driving for 70 miles at highway speeds, I have about 2 miles of 45mph
descent into town (almost no throttle) followed by about a half-mile
of 25mph climbing up a mild hill to my apartment.  So what I saw on
the plugs may not reflect the reality of what the engine would tell me
at the time of the problem.

Aaron Whiteman
Pullman, Washington


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