So it's finally started to get cold here in NE Tennessee. Not that I have been looking forward to it or anything.

Yesterday when I left for work it was around 60 degrees (16 C). It was predicted to get below freezing yesterday morning but it didn't get that cold. Around 40 degrees (4 C).

Based on my experience tuning Webers on Fiats, My Citroen feels like it needs a larger main jet when driven at temperatures below 60F/16C. When it was in the 90s (~35C) this summer the car ran great.

I've found any jetting issue will show up when the temperature starts to drop. A car will run fine even if too lean in the summer but once the temperature starts to drop below 60F/16C a lean running engine will chug, backfire, etc. I guess the colder the air the more dense it is.

But my 2CV has a stock engine so I don't think that's necessary. The engine has some flat spots and some acceleration issues unless I keep the RPMs built up. Meaning at lower RPMs, the engine feels like it's not making any power unless I up shift.

I thought perhaps if I increased the idle mixture might give me a bit more fuel but the engine does not stall, idles smooth and doesn't backfire like my Yugo did before I increased the main primary jet size so I think I need to leave the idle mixture and main jetting alone.

Would driving with the choke slightly closed have any effect? Or would that just act as a restrictor plate and decrease power?

I understand that in temperatures below 50 degrees (10 C) your supposed to run a blanket over the grill. Well I don't have one so I improvised with a piece of cardboard with two holes cut out roughly the same size as the dump tubes held in place with two zip ties until I can get one.



So I drove the car to work tonight and it was around 60F/16C. I felt plenty of airflow from the floor vents and was toasty warm. Although I really don't need to heater on at that temperature. The engine did seem to run a bit smoother with the fan blanket.

I understand one issue with blanking the fan is it reduces the air velocity to the cabin when using the heater.

This morning it's predicted to get down into the 20s (-6C to -1C) so I'll see how this works.

Here is my question. I don't want to overheat my engine. The holes I cut were roughly the same size as the dump tubes in the heater exchangers. As long as I can feel airflow from the heater, is that sufficient?

At what temperature should the fan be totally covered? At what temperature should the fan NOT be covered at all?

Is there a "science" the fan blanking on 2CVs?

I would imagine since these cars run OK in North Africa where it get's really hot (48C perhaps) running the blanket at 60F/16C with two holes is not any different.

One thing I thought might help the engine run better at colder temperatures was to drill a 2" hole in the driver's side heat exchanger and pop rivet a snout and run a hose to the inlet to the air cleaner. That way the engine is sucking in warmer air and in theory should run better but I've never heard of anybody doing this on a 2CV. Any thoughts on that?

Yet another thing I've read is before starting the engine to turn the key on for a few seconds but not start the engine. I have never heard of doing this. What's that supposed to do?

I have also heard 2CVs are bad about carburetor icing. When I Google this, all I come up with is on aircraft engines. Years ago my first car was a 1981 Honda Prelude and my Dad had a 1984 Ford Bronco II that both experienced carburetor icing.

The problem occurred only if there was snow on the ground which was melting, the air temperature was higher than freezing usually around 45F/7C and when driven at speeds above 45 F. In other words very humid conditions and high air velocity. If I was puttering around town at 30 mph, this did not occur.

If the temperature was below freezing, the air was dry, this never happened.

With the Prelude I chocked this up to running an open air cleaner. So I installed the factory air cleaner and had no more issues.

I'm not sure what the problem was with the Ford. My father didn't believe me until he got the truck out on the highway and it happened to him. Because he drove the truck back and fourth to work and seldom got above 30 mph.

Unless the heat riser was not working. But technically the heat riser should shut off once the engine warms up. Not act like a thermostat.

Cheers!

Normal perceived wisdom on a grill muff is on at 10C and below, off above 15C - if the carb is original and not been re-jetted, the primary maybe too small for modern fuels and could be running too lean - primary jet - the little fecker that's accessed via the nut/plug at the right rear of the carb looking from front of car - if it's not original, should be marked 1.07 or larger if it's a 26/35 Solex

I think your cardboard version is probably about the same size intake holes as the muff. I doubt its too critical.
I don't use my muff much at all, the car has been fine running without it on long journeys at -5 celsius or whatever, but I definitely notice it warming up quicker on short journeys if I use it. Never had an issue with carb icing, I think thats what the pipe on the manifold runs under it for maybe.

Regarding warmed air for the intake - I thought cold air was better for power? And its not like we have much of that to play with

yes up to a point but given the charge does a 90* turn and then off down relativley long inlets carburation on A series is a bit of a chore. The hotspot under the carb is there for a reason and in this weather a little heat keeps the petrol in suspension

A #58 drill bit through the primary petrol jet and the flat spots, etc., will be gone.
The original jet will have been 0.102mm in diameter, after the 'treatment', closer to 0.107mm...

What about jet size for a Dyane carb

Are you really trying to tell that is cold..?

Coldest what I have experienced with my Dyane, was -42C. Without re-jetting carb. And nowadays, with EFI, some degrees below -30C and everything worked like a charm...

You propably need to re-jet your carb, not because of "cold" but because of the fuel is something different than it was when these little engines was made...

Some days ago I started my only carburated car at -10C, it still has its original jetting on all three double-Webers what are installed on -71. No need to alter them, if there is believing to Lambda sensors (not original, installed with MS2 what controls only the ignition)...

https://www.youtube.com/watch?v=nYbd4aG6fBA
A short video of my carb -engined car running at -10C...

Oh good point about fuel. Often much more ethanol in the US. We are still around 5% in the UK.

Good point. I've been running e10 93 octane (RON+MON/2 method) since I've had the car. They say engines get 15% less mileage on e10 versus 100% gasoline. I have not found any evidence of that to be honest.

I don't know what you guys are using now for an octane scale so here is the equivalent chart.

http://www.pencilgeek.org/2009/05/octan ... sions.html

I know this car does not need premium fuel but the guy who owned it before me was not a car enthusiast. He was a contractor and took the car in leau of payment for some work he did on a guy's house. I thought perhaps the fuel in the car was quite old so I figured running 93 for awhile might purge some of the stale gas out. That's my theory anyway.

The car did seem to run better this morning using the cardboard muff. It was around 30F or -1C.

Yes, colder air should yield denser air and more power. But my theory was in colder air, fuel does not atomize as well on carburated engines in colder temperatures.

On fuel injected engines this is a total different story. Fuel is injected directly at the intake valve (or closer to the combustion chamber) so it should atomize as soon as it hits a hot valve.

Another thing is with carburated engines, the engine is going to get the same amount of fuel no matter what the ambient temperature it is. So when it's colder outside, the air contains more oxygen but the jet is supping the same amount of fuel.

I tend to think it's better to jet an engine during cold weather than in the middle of summer just for that reason.

My Yugo for example. I went from a 1100cc engine to a 1500cc engine. I rejettted the secondary for the turbo but never bothered to mess with the primary. But I did rejet the idle. Because the Weber tuning guide said if the mixture screw was turned out more than 2 turns (something like that) to step up to a larger idle jet.

The engine ran great at 95F/35C. At temperatures below 60F/15C the engine started to run rough under cruise. At temperatures around freezing, the engine would really run rough and backfire at times.

I can't remember but I went from a 100 to a 125 or something and now the car runs smooth under all conditions.