I live in frosty Minnesota. This past weekend I went out and tried to
fly by .40 sweet stik for the first time with temperatures in the 30's
(Fahrenheit).

It turns out my engine would sputter and die after a few seconds at
full throttle, but would run just fine at half throttle. The engine
idles fine. It's a 1981 vintage K/B 40 if that matters. It's always
run reliably and never quit in the air until this past weekend with
the cold weather. The day before I ran a full tank of fuel through it
at full throttle in my garage without any problems.

I just bought the fuel (10% nitro) so it is fresh. The glow plug is
brand new. The fuel seems to be flowing well and I don't see any
evidence of a pinched fuel line or any sort of clog. The engine
starts fine in the cold weather.

I tried all sorts of combinations of a little leaner, a little
richer, way leaner, way richer, etc. Nothing seemed to help.

One thing I noticed was that right as the engine started to sputter
and die I could see little droplets of fuel dancing around inside the
venturi.

After the engine sputtered and died in this manner, it was hard to
restart (as if it had totally flooded.) If I just stopped the engine
normally, it would start right back up again without problems.

Those are all the symptoms and information I can remember. This is
the first time I've tried to run the engine in temps below 50-60F.

Any fellow northerners have any cold weather engine running tips? Do
I need to upgrade to engine-2.0? How do I keep my thumbs from
freezing off?

If anyone is is interested, here is the photo/video record of my day
out with my plane:

http://www.menet.umn.edu/~curt/Photos/Models/SweetStik/

Pretty windy. 4 flights ... 3 dead stick landings with engine
problems. All landings were nice and gentle, plane went home intact
... I think that's a new record for me. :-)

Curt, I am from NW Iowa and I flew last weekend as well, but I had no
trouble. Never even touched the settings. I have a OS 40 fp and a magnum 52
4 stroke. both ran fine. The temp was 40 degrees out. Is it possible that
the fuel is leaking around the needle valve? I had that problem with my OS
40 fp....and I solved the problem with a piece of fuel tubing as a gasket.
Just a thought....
 

Colder weather = denser air = richer setting required to obtain correct
mixture of fuel/air, eh? :)

I am in Edmonton Alberta. I fly frequently when it is darn cold. My Lux
.46 refuses to start when it is cold. If I give it a tiny shot of WD 40 it
fires right up. After that It is really great. I adjust the needle in this
thing twice a year. Once in the winter and once in the summer. Some people
have commented on the new WD-40 not working as a starting fluid as they
changed the propellant. I purchased a new can last year and it worked just
great. Winter flying is great, we get much more power due to the denser air
and a dog of a plane handles like a dream. Touch and goes dragging a
wingtip in the snow is a riot. The snow tends to absorb high energy impacts
better than grass for some reason.

If you want I can post some of my winter pics in the binaries group.

As the temperature drops, you will have to enrich the mixture.

Some engines run better than others in low temperatures but none that I've
had run as well as they do when it's over 50 F. There are a couple of things
that will help. To start the engine, use a few drops (4-6) of naphtha as a
prime. This works very well and will usually light the balkiest engine. Adding a
few percent acetone to the fuel also helps (2-3%). I've used these 'helpers' to
fly down to 6 degrees F. If none of this is sufficient, you must be trying to
fly when it's too cold out! :-)

Brian

"You can always tell an Engineer....

But you can't tell him much."

Unfortunately I don't have an answer. Just some words of encouragement (or
is that discouragement?)

Engines should have no problems at that temp. Maybe a little additive to
start (ether), but usually not even that. Although diagnosing a problem
via the written word is nearly impossible, it sounds like you have fuel
delivery problems. Either crap in the needle valve housing or air leakage
around the needle valve stem. I have a piece of fuel tubing around my K&B
40 needle valve stem to stop this leakage. Not sure if I have the same
carb as you though. Big clunky square thing ??.

Maybe, if you are using a "cooler" plug (OS #8) try a warmer one (Fox R/C
Long).

Cold weather should not create its own set of unbeatable problems.

Now I've heard that when it gets REAL cold (minus 10....you know, when
you Minnesotans put away the shorts and wear long pants <g>) the paraffin
in the fuel starts to coagulate and little balls form.