[Public-List] A4 Question

[pat nolan]

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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