[T3] Old Type IIIs (Exhaust Tester)

[Dave Hall]

You're right, I didn't give the complete answer.  Unburnt hydrocarbons would
also be detected if misfiring is occurring due to over-rich or too lean a
mixture.  If there is proper ignition firing, the hydrocarbons (from the
fuel) will be burnt, but perhaps not completely, giving a higher CO reading.
High HC content in the exhaust gases with OK CO level means ignition, valve
or compression problems.  Been there, had to do a valve job on my son's
Polo.

There were specs for CO for carbs of 3-4% and 0.5% +/- 0.5% for FI that I've
seen from factory literature somewhere - maybe a service bulletin or a later
published servicing guide.  I don't think it appeared at the time in the
factory manuals - the measuring equipment at the time wasn't universally
available other than at places specialising in Tune-ups (Krypton? eg).

When I checked my FI with a 'domestic' CO meter it barely read at all -
about 0.1%, but I wouldn't put a great reliance on the actual % at that
level in unsophisticated equipment.

My twin carb Type 3 runs fine at 3% CO. but I usually tweak it a bit richer
than that - maybe 3.5% just to be a bit kinder to the engine, and it is less
likely to 'bog-down' when pulling away.  If it gets to say 7%, the exhaust
gets quite smelly - the way most classic cars seem to smell! 

Modern cars with a catalytic converter shouldn't be putting out anything
significant for CO level.  Fortunately the old hose-pipe suicide has become
a thing of the past.  I don't have a modern petrol (gas) car - the diesel
test they do is just for smoke particles.  In any case they have Cats so
shouldn't be emitting CO anyway.

Dave.
UK VW Type 3&4 Club
===================

-----Original Message-----
From: type3-vwtype3.org-bounces at lists.vwtype3.org
[mailto:type3-vwtype3.org-bounces at lists.vwtype3.org] On Behalf Of Jim Adney
Sent: 05 March 2011 04:13
To: type3 at vwtype3.org
Subject: Re: [T3] Old Type IIIs (Exhaust Tester)

On 4 Mar 2011 at 20:15, Keith Park wrote:

> Well, its not that simple.  I have an LC1 and it depends on where you 
> put your O2 sensor and what condition the engine is under... youll get 
> in the low 10's under heavy acceleration and upper 14's or 15 under 
> light throttle or deceleration.  Under normal cruising conditions you 
> want to see something in the 13.2 - 14.1 area.

Keith's right, we've been oversimplifying it. It varies over quite a range
depending on the operating conditions, but the only conditions it can be
measured under by most shops will be at idle. 14.7 is the theoretical ideal
number, but I'm not sure where most of our cars actually fall.

If you find a shop that has an exhaust analyzer, they will probably be most
likely to measure CO levels. They may know what to expect, but they're most
likely to be familiar with newer cars which will have lower CO than ours.
I'm not sure what ours should be. I'd guess 1-3%, but I could be wrong. I'm
not aware of any specs that VW published on this for Type 3s.

Were there specs on this, Russ?



--
*******************************
Jim Adney, jadney at vwtype3.org
Madison, Wisconsin, USA
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