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-----Original Message-----
From: William R. Bayne
[mailto:[EMAIL PROTECTED]
Sent: Wednesday, April 06, 2005
2:20 AM
To: Ed Burkhead
Subject: WRB Re: [COUPERS-FLYIN]
carb help
RLYFLYIN (WRB via Ed Burkhead's computer-I can't post directly)
Please send responses directly to the list or to me, Bill Bayne @
<[EMAIL PROTECTED]>
Hi All (WRB speaking),
Like Ed, I'm not certificated as a mechanic; but I have access to most (if not
all)
materials that certified mechanics refer to (or should) and some they may lack;
and I CAN read.
Raising the temperature of the fuel/air mixture with carb heat helps the atomization
of liquid fuel by the carburetor in cold air. The induction system of our
little four-
bangers is NOT very well balanced (even when well sealed); and old, hard
induction
hoses can hide significant (and hard-to-find) air leaks.
Anyone with a four-probe EGT or CHT display can visually "even out"
some of the
imbalance with judicious application of just enough carb heat to improve
vaporization.
This causes an increase in idle r.p.m. (if sufficient heat is available) and
smoothness
("runs better"), and can also improve cruise efficiency in cold air.
The Stromberg has an entirely separate idle metering system because the main
metering system will not function at low engine speeds. The idle system
functions
to approximately 1000 r.p.m. A needle-valve type adjustment is provided with
which to adjust idle fuel flow for the correct fuel/air ratio at such low
speeds. If it's
not right, have your mechanic adjust it. Follow proper safety precautions doing
so.
With the engine warm and throttle closed against the stop (but not locked),
slightly
loosen the idle adjusting stop clamp screw. Turning the idle speed adjusting
screw
to the right (in) leans and to the left (out) enriches. Set it for smoothest
operation at
approximately 600 r.p.m. and a bit on the rich side for safety. Tighten the
idle speed
clamp screw, and secure the needle valve with lock wire.
Lloyd didn't mention his ground "test" r.p.m. applying carb heat.
Assuming it was below
1000 r.p.m., there would be no correlation to the mixture supplied in flight by
the main
metering jet/system at higher r.p.m.
Yes, the Stromberg has extra enrichment at full throttle for cooling purposes.
Those
who fly for extended periods at "full throttle" without leaning above
5000' waste fuel.
If they instead lean until the r.p.m. drops a bit and enrich just enough to
recover the
lost r.p.m., they can avoid unintended (and undesirable) "extra
enrichment" in "cruise"
(as opposed to "climb") mode and enjoy a lower fuel burn rate at the
same speed.
Regards,
William R. Bayne
<____|-(o)-|____>
(copyright 2004)
--
On Apr 5, 2005, at 11:49 PM, Ed Burkhead wrote:
Lloyd
asked:
> I
have a question for you, why does my engine run better on
>
the ground when the carb heat is applied ?? I also have the
> Stromberg.
Yes, I am an A&P ....But have . no experience
>
with these carbs. Help.
Lloyd,
I’m
not a mechanic and I shouldn’t play one on the Internet. I got hives
answering that previous question and hope I didn’t step on it.
Here are thoughts about your
situation:
If
it’s running rough on the ground when set to full rich but improves when you
pull carb heat – maybe you’re running too lean on the ground. Carb heat
thins the air as it heats it so it richens the mixture.
As
you climb, the mixture gets richer and richer. If you’re too lean on the
ground, you may be just right higher up so it may run just fine in
cruise. I think the Stromberg richens the mixture at full throttle, like
many other aircraft carbs, so that may be why you’re not getting detonation
during full-power climb.
Then
it follows that if you’re too lean on the ground, you need some maintenance.
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