[Public-List] A4 Question

[Bill Ydel]

Guys, I was going to say that ice could not be part of my problem since this is Charleston, "SC" but tonight it is supposed to go down to 22 deg and this town is in a panic.

Bill Ydel

Sent from my iPad

On Jan 6, 2014, at 5:01 PM, Michael Connolly <crufone at comcast.net> wrote:

> Steve, 
> Carburetor ice is a distinct possibility. Especially as you have described your conditions of loss of power. There is no carb heat on our boats as an aircraft engine would have. On my engine (Gray Marine) there is really only in place a back fire arrestor not truly an air filter. This is all metal and would do nothing to keep the carb inlet temp elevated.  High humidity with temps just above freezing is a perfect scenario for carburetor ice. 
> Michael #133 
> 
> ----- Original Message -----
> 
> From: "Stephen Gwyn" <stephen.gwyn at nrc-cnrc.gc.ca> 
> To: public-list at lists.alberg30.org 
> Sent: Monday, January 6, 2014 4:29:00 PM 
> Subject: Re: [Public-List] A4 Question 
> 
> 
> 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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