Re: Vacuum leak tracing

[Damian Carvolth <d.carvolth@xxxxxxxxxxxx>]

>I haven't physically checked for quite a while, but from
>recollection, I'm not sure that there's enough access to do this in
>the area under the carbs and manifold. I seem to recall that there
>isn't enough room or access to get an aerosol with a nozzle-tube
>into that underside area and aimed even vaguely upwards, but I
>could well just need to look again and try harder next time.  The
>thing I was wondering was whether somebody had sussed out
>some better way to troubleshoot this inaccessible area...... but it
>looks like there's not.   No free lunches eh?

An air blast (with an air nozzle or similar) will do the same thing as will
pouring or puffing petrol around the area.

The theory is if there is a leak the fuel or air will upset the balance and
the idle will change.

Some people worry a lot about pouring neat fuel over their engine while it's
running but I haven't set one alight yet...you need both a stray spark to
jump externally and vapourised fuel in a combustable mixture with the air
precisely where the spark jumps. This hasn't happened to me yet...

Still fluey...:(

oh and the other one...

Subject: re:Vacuum leak tracing
Braden recommends a gadget called a Colourtune in his Weber
book..... fits in plug hole and (shows) the mixture colour.  One cyl
will come up lean if there is an air leak.  
Peter
>>>>>

Hmm, thanks for the idea. I've heard of the Colourtune product for
many years but have never had one.
One problem I can see with this idea, however, is that it doesn't
really get round my original difficulty, which was how to identify
whether there was a leak in that inaccessible area under the carbs
and manifold. The Colourtune might well tell you there's a vac leak
SOMEWHERE associated with a given cyl, but so would the
aerosol spray, and neither way is the best for checking out the
underside to locate a leak.  Further confirmation I guess that, with
an Alfa, there're no free lunches....... ah, but what the heck, when
they're going, they're more than worth it all aren't they?

Well if you want to be that specific you have 2 options. You can remove the
manifold and look at the joining faces (how much work is this ?) or you can
introduce a targeted blast of air or spray of fuel to the precise area you
want to test. How you introduce that is a simple mechanical problem. The air
for example can be channelled through some 1/8" steel tube, and since it's
air you don't ahve to worry about wasting some on the way there.

I don't think a colourtune would be a reliable method. The trouble is it
only indicates the mixture in the combustion chamber. If you have a leak it
usually hasn't appeared suddenly and so you've probably partly compensated
for it in previous tuneups. Also vacuum gauges would have to be pretty
accurate to pick up a slightly lesser depression due to a leak...maybe some
really good manometers but I doubt it....

Std disclaimer on advice and my current state of mind...
Damian Carvolth
"I'm just a startled bunny in the headlights of life", L.J. Young
damian@domain.elided 
http://www.brb.dem.csiro.au/unrestricted/people/CarvolthDamian/
http://dove.mtx.net.au/~bryanb/members.htm#Damian Carvolth

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