Subject: Re: [TR] rough idle

From: Mark J Bradakis <[email-masked]>
Date: Mon, 17 Sep 2018 21:46:39 -0600

On 9/17/18 12:57 PM, Sujit Roy wrote:
> Will an electronic ignition help and reduce a rough idle condition?
>
> I have a Stag (V8) with a Lumenition optical module it runs rough at 
> idle. I was under the impression that changing to electronic would.
>
> Is it time to have the distributor looked at?
>

If the rough idle is due to ignition issues, changing the ignition may 
help.  If the rough idle is not due to ignition, changing the ignition 
may not make any difference at all.

mjb.

** [email-masked] **

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From: Sujit Roy <[email-masked]>
Date: Tue, 18 Sep 2018 09:01:35 -0700

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Hi Randall,
Where would I start? I don't think I have a vacuum leak. The carbs are
balanced. The car runs OK. Fuel consumption is poor but has been for years.
I have not adjusted the carbs with regard to fuel mixture in a long time
Should I start here?

Sujit

On Tue, Sep 18, 2018 at 6:52 AM Randall <[email-masked]> wrote:

> Short answer: Maybe.  Depends a great deal on why it idles rough.  A V8 has
> to be really sick before it becomes noticeably rough; I doubt you would be
> complaining about roughness from spark scatter.
>
> -- Randall
>
> > -----Original Message-----
> > From: Triumphs [mailto:[email-masked]] On
> > Behalf Of Sujit Roy
> > Sent: Monday, September 17, 2018 2:58 PM
> > To: Triumphs
> > Subject: [TR] rough idle
> >
> > I have a Stag (V8) with a Lumenition optical module it runs
> > rough at idle. I was under the impression that changing to
> > electronic would.
> >
> > --
> > Sujit Roy
> > Cupertino, California
> > https://triumphstagblog.wordpress.com/
> >
> >
> >
>
>

-- 
Sujit Roy
Cupertino, California

https://triumphstagblog.wordpress.com/

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<div dir=3D"ltr">Hi Randall,<div>Where would I start? I don&#39;t think I h=
ave a vacuum leak. The carbs are balanced. The car runs OK. Fuel consumptio=
n is poor but has been for years. I have not adjusted the carbs with regard=
 to fuel mixture in a long time Should I start here?</div><div><br></div><d=
iv>Sujit</div></div><br><div class=3D"gmail_quote"><div dir=3D"ltr">On Tue,=
 Sep 18, 2018 at 6:52 AM Randall &lt;<a href=3D"mailto:[email-masked]"=
>[email-masked]</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quo=
te" style=3D"margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"=
>Short answer: Maybe.=C2=A0 Depends a great deal on why it idles rough.=C2=
=A0 A V8 has<br>
to be really sick before it becomes noticeably rough; I doubt you would be<=
br>
complaining about roughness from spark scatter.<br>
<br>
-- Randall=C2=A0 <br>
<br>
&gt; -----Original Message-----<br>
&gt; From: Triumphs [mailto:<a href=3D"mailto:[email-masked]=
et" target=3D"_blank">[email-masked]</a>] On <br>
&gt; Behalf Of Sujit Roy<br>
&gt; Sent: Monday, September 17, 2018 2:58 PM<br>
&gt; To: Triumphs<br>
&gt; Subject: [TR] rough idle<br>
&gt; <br>
&gt; Will an electronic ignition help and reduce a rough idle condition? <b=
r>
&gt; <br>
&gt; I have a Stag (V8) with a Lumenition optical module it runs <br>
&gt; rough at idle. I was under the impression that changing to <br>
&gt; electronic would.<br>
&gt; <br>
&gt; Is it time to have the distributor looked at?<br>
&gt; <br>
&gt; <br>
&gt; -- <br>
&gt; <br>
&gt; Sujit Roy<br>
&gt; Cupertino, California<br>
&gt; <br>
&gt; <a href=3D"https://triumphstagblog.wordpress.com/" rel=3D"noreferrer" =
target=3D"_blank">https://triumphstagblog.wordpress.com/</a><br>
&gt; <br>
&gt; <br>
&gt; <br>
<br>
</blockquote></div><br clear=3D"all"><div><br></div>-- <br><div dir=3D"ltr"=
 class=3D"gmail_signature" data-smartmail=3D"gmail_signature"><div dir=3D"l=
tr"><div>Sujit Roy<br>Cupertino, California</div><div><br><a href=3D"https:=
//triumphstagblog.wordpress.com/" target=3D"_blank">https://triumphstagblog=
.wordpress.com/</a><br><br></div></div></div>

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From: "Randall" <[email-masked]>
Date: Wed, 19 Sep 2018 10:09:48 -0400

> Where would I start? I don't think I have a vacuum leak. The 
> carbs are balanced. The car runs OK. Fuel consumption is poor 
> but has been for years. I have not adjusted the carbs with 
> regard to fuel mixture in a long time Should I start here?
> 

I would start with a major tune-up; including checking valve lash and
compression.  I know valve lash is a pain on a Stag engine, but it's often
overlooked for that reason.  And lack of lash caused by valve seat recession
will show up first as rough idle.  Look at the old plugs for signs of oil or
carbon fouling, etc.

Another piece of that is hooking up a timing light, to check for spark
scatter at various rpm and that the timing moves smoothly as you rev the
engine slowly up and back down.  I don't have the exact numbers handy, but
generally total advance (the farthest it will move at higher rpm) is very
roughly 3 times the idle advance (with both vacuum retard and vacuum advance
if present disconnected).  Idle timing should be somewhere in the
neighborhood of 10 BTDC (with retard disconnected), while max should be
roughly 30 BTDC.  My point being that you should see movement of roughly
twice the distance between the idle timing mark and TDC.

Checking mixture is good, too.

Use an ohmmeter to check each spark plug wire, from the terminal inside the
distributor cap to where it clips onto the spark plug.  The exact resistance
will vary a bit depending on length (assuming you are using carbon core
wires), but all should be somewhere between 5K and 15K.  A single higher
value means a bad wire or bad connection (probably time to replace the whole
set).

Since this is a long term condition (since it was rebuilt the second time?)
and includes poor fuel mileage, I would also make some attempt to check
valve timing.  I don't have my books handy, so I'm not sure what the best
way to do that on a Stag is.  But if all else fails, you can attach a degree
wheel, find TDC with a piston stop, and take several readings around where
the exhaust closes and the intake opens.  The point where they match (equal
lift) gives the cam timing, which ISTR should be around TDC on a Stag.
Obviously you repeat this for the other bank/cam.

Give the cam lobes the hairy eyeball while you're in there, for damage
around the high point of the lobe.

-- Randall