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Re: Plug Color Mystery

To: Roadster list <datsun-roadsters@autox.team.net>
Subject: Re: Plug Color Mystery
From: Marc Sayer <marcsayer@home.com>
Date: Thu, 15 Mar 2001 09:37:43 -0800
Teddy Seidenfeld wrote:
> 
> > Date: Tue, 13 Mar 2001 19:58:31 -0800
> > From: Marc Sayer <marcsayer@home.com>
> > Subject: Re: Plug Color Mystery
> > Nathan Ruffcorn wrote:
> > >
> > > Hey all-
> > >
> > > The weather was great today! I've been able to get the roadster out for
> > > the past three days straight. The bugs are slowly getting worked out,
> > > making each run more enjoyable. As always, it attracts lots of attention.
> > > I'm especially enjoying the 3.9 rearend/2L combination. <grin> It's easy
> > to
> > > accidentally bark the tires when pulling away from a stop light. For
> > > leasure driving, out of traffic, I routinely start in 2nd and skip to 4th.
> >
> > >
> > > In an effort to get everything just right, after each run I have been
> > > pulling the # 1 and # 3 spark plugs to judge the mixture of each carb. The
> >
> > > plugs have been whitish/grey so I've been gradually richening it up.
> > > Yesterday, out of curiosity, I decided to pull all the plugs. I was REALLY
> >
> > > surprised to find #1 and #3 the same color (whitish/grey) and #2 and #4
> > the
> > > same (brown). What am I missing?! I admit, I'm no master tuner but I know
> > > that cylinder #1 & #2 and #3 & #4 should at least correspond together.
> > >
> > > Other factors (symptoms):
> > > -Rebuilt carbs from Z-therapys
> > > -Seems to surge a bit at highway speeds (65-70mph)
> > > -Hesitates under gradual acceleration, but seems to immediately "come
> > alive"
> > > with a heavier foot.
> > >
> > > Please let me know if I'm missing anything really obvious.
> > > Man these cars are fun!!

This just goes to show, I should never answer posts when I am tired. While my
original reply was all true, it has nothing to do with what is described here. I
got the cylinders confused and thought he was describing the pattern I
explained. But I see now his pattern is something else. I apologize for creating
any confusion. I agree that valve adjustment is the place to start. I would also
check the ignition system. Try swapping the plugs around (put the plugs from 1 +
3 into 2 + 4 and vice versa) and see if the pattern reappears. A word of warning
about plug color, though. The only way plug color can tell you anything is if
you start with clean plugs or run at a steady speed for at least a minute or so
to "clean" the plugs, and cut the engine as soon as your test run is done. If
you leave the engine running while you come to a stop, get off and on the gas,
or let it idle at all, the reading will be affected. Also many fuel additives
nowadays mess up the coloring of the plugs and make plug reading impossible.

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