[Public-List] A4 Question

[Dominic Amann]

Hmm. I was just thinking about how one could make a heat exchanger. Of
course if the carburetor had been nestled more closely to the exhaust
manifold...
 On Jan 6, 2014 10:03 PM, "pat nolan" <pnolan33 at yahoo.com> wrote:

> I wrapped a piece of heavy copper wire around the manifold and then around
> the carb throat . It transferred heat much faster and solved the problem .
>
>
>
>
> On Monday, January 6, 2014 12:29 PM, Stephen Gwyn <
> stephen.gwyn at nrc-cnrc.gc.ca> wrote:
>
>
> My A4 sometimes runs less than perfectly in winter. It's
> usually hard to start if the temperature is close to
> freezing. Then it will run fine for 10-15 minutes, before
> losing a lot of power in gear. I'll motor out the marina
> in gear at idle, then speed up when I get out. A minute
> or two after that, as I'm in the middle of the current
> (and the rocks), the engine starts to slow down. Opening the
> throttle brings it back up to normal power, and after 1-2 minutes
> the engine starts to over rev. I then close the throttle
> a bit and the engine runs fine for the rest of the day.
>
> The loss of revs only happens sometimes. It only happens
> before the engine reaches operating temperature. It never
> happens in summer.
>
> I have some theories:
>
> 1) Ignition system is damp or otherwise compromised by cold or
> possibly age. Damp isn't good for the points in particular.
> I replace the points, condensor, cap and rotor
> in the spring, so in winter they are at the end of their service life.
> But I don't think this is the case, because then the engine would
> run poorly from the start.
>
> 2) Condensation in the fuel tank, which then gets into the fuel.
> More likely. Winters in Victoria are very humid and certainly the boat
> gets a lot of condensation in winter. But I have an over-sized
> fuel filter/water separator which I change regularly, so I'm
> moderately sure that's not it.
>
> 3) Carburetor icing. If you put your hand on the carb throat
> when the engine is running, it's a lot cooler than the ambient
> temperature, and certainly a lot cooler than the nearby manifold,
> which gets quite hot. On cold humid days, I've noticed a thin coating
> of frost on the outside of the carb. My guess is that frost is
> forming on the inside of the venturi, restricting the flow of the fuel/air
> mixture into the manifold and into the cylinders. Eventually, however
> the manifold fully warms up and starts conducting heat to the
> carb. The ice melts, the venturi clears and the engine starts
> working normally again.
>
> SG
>
>
>
> --
> ------------------------------------------------------------------------
> Stephen Gwyn                       | Tel: 1-250-363-3136
> Canadian Astronomy Data Centre     | Fax: 1-250-363-0045
> Herzberg Institute of Astrophysics | Cell: 1-250-885-6969
> 5071 West Saanich Road             | E-mail: Stephen.Gwyn at nrc-cnrc.gc.ca
> Victoria, BC, V9E 2E7, Canada      | http://astrowww.phys.uvic.ca/~gwyn/
> ------------------------------------------------------------------------
>
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