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Posted By: Daniel Recently I opined with a recommendation of two extremely well written articles on dealing with two strokes.
One was George Sychrovsky's excellent piece "Two Stroke Engine Mystery Solved", dealing largely with how to correctly operate one of the beasts:
The other was an equally excellent piece by Tom Olenik called "Tuning The 2-stroke Aircraft Engine", which you had to join one of the Yahoo groups in order to access. Tom has graciously given his permission for me to repost that piece here to make it more accessible.
For those who don't know of him, Tom makes his living selling and caring for ultralight & very light plane engines. He's a regular contributor to the Engines-UL group on Yahoo & backs his comments & advice with detailed logic and a lot of experience. He's a guy (like George) I would happily do business with. No, he won't hang on the phone giving free advice all day, he's got paying customers asking for attention too, though more than one flyer who's sourced an engine elsewhere has subsequently put him on "retainer" to get his advice! Please bookmark his site and consider him for your needs:
At any rate, here's his article:
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From: "Tom Olenik" Hi guys,
As promised, I am going to go through some things that may help
No matter who makes the engine, the first thing I do is lean the
Most of the time with a 2-stroke, you can not lean to peak
Once appropriate measures are taken to secure the plane, start
One thing you may run into is that you could run out of
Now that you have your idle set, you are ready to try your mid
For reliability and engine longevity reasons, I take exactly the
Once the mid range is set, with the engine properly warmed up,
If your full power EGT is fairly low, like in the 800 range,
Since mixture effects the power output of the engine and
These are the exact same steps I use when setting up an engine
As always, let me know if you have any questions.
Tom Olenik
------------------------------------
Date: Thursday, 3 June 2004, at 9:43 a.m.
http://curedcomposites.netfirms.com/twostroke.html
http://www.buyitsellitfixit.com/
Date: Sun Sep 1, 2002 11:53 am
Subject: Tuning The 2-stroke Aircraft Engine
with properly tuning the 2-stroke aircraft engine.
idle mixture. Even if you think you have a smooth running engine
at idle, you may still get problems at other power settings from
excessive fuel that loads up or even harmful long term effects
like excessive carbon build up. Often people go changing main
jets or needle clip positions because of fowling spark plugs or
what ever when the problem is really coming from a rich idle.
efficiency like in a Cessna or the like because the engine will
seize before you get there. However, at low engine speed you CAN
lean to peak efficiency without damaging the engine. To do this,
I would suggest securing the airplane so it can't roll away,
because as you lean the mixture, your idle speed is going to
increase and may increase enough to make the plane roll away.
the engine and listen carefully at idle. Listed for occasional
bumps or misses. Listen to the general tone of the engine. Feel
the airframe for vibration. This is sort of like tuning a guitar
by ear. Then shut it down. The 2SI engine really is usually a
smooth running engine at idle even when it's too rich, so you
may have to go by RPM more than the smoothness. RPM will
increase as you get closer to peak efficiency. With the Bing 84
carb or Bing 54 carb, start turning the idle air screw out
(counter-clockwise) about 1/2 turn (180 degrees). This would be
the smaller screw that is recessed into the carb. Turning it out
allows in more air and effectively leans the mixture in the idle
RPM range. As you turn it out, keep track of how far you have
gone. After each half turn, start up the engine and listen and
feel for bumps, misses, roughness and the general tone of the
engine. Generally a deeper tone will be richer and a higher
pitched tone will be leaner. Continue to go through this until
the engine seems to be running completely smooth. As smooth as
glass. Note where you are on the air screw adjustment at that
point.
adjustment on the airscrew. If you turn it out far enough to see
the o-ring that seals it, you need to go to the next leaner
idler jet. If you change to a leaner idler jet, start out with
the airscrew turned out about 1/2 turn and continue with the
process. Even if it seems like it is smoothed out, note that
setting and continue. You will eventually get to a point where
the engine will decrease in RPM and/or die or not want to run.
Note that point as well. I would then set your idle air screw
about mid way between where it seemed to totally smooth out and
where it was too lean to run. That way you should not need more
adjustments with changes in the weather or density altitude
unless those changes are severe.
range. NOTE: leaning the idle can sometimes have some effect on
the midrange and you may want to start out in the richest
(lowest clip position) needle setting until you know where your
EGT is going to be. With the engine properly warmed up, increase
the throttle into the 4000 - 5000 RPM range. Make movements with
the throttle watching your EGT for the hottest spot and just
make a mental note of where your engine has it's hottest EGT. Be
cautious about staying within limits on all your temperatures
because now you are running at engine speeds that can cause
damage if mistakes are made.
opposite approach to mixture at higher power settings as I do
for idle mixture settings. What I mean is that I like to make
the mixture rich until it runs a little bit rough, then lean it
out a little from there. This is just the opposite that you
would do a in Cessna or other GA type aircraft. While you are
searching for that hottest spot in your mid range, keep your
ears open for any little misses or bumps, and feel for any
momentary waves of vibration in the airframe. Those are all
signs that the mixture is bordering on being too rich. The
reason you are looking for the hottest spot in your EGT is so
that you don't make an adjustment that would put that over
limits. Each position on the jet needle will change the mid
range EGT approximately 50 degrees + or -. If you don't notice
any roughness or other signs of being too rich in the mid range.
Make it a little richer. If you are already in the richest
position on the jet need and well within temp limits, you might
just leave it alone here. Otherwise you would need to go to a
different needle jet to make the mixture richer. If the mid
range is rough and acts like it is rich and you are well within
limits on your EGT, you can move the clip to the next leanest
position. When leaning the mixture always make small incremental
changes because too lean will cause damage often without
warning. So if your EGT is 900F or 1000F and the engine is
running rough in the mid range, try moving to the next leaner
needle position. Do this until either the engine smoothes out in
that range or you come within 50F of your upper EGT limit. If
your EGT limit is 1200F and you are at 1150F, you probably do
not want to make another adjustment any leaner.
you can do a static run up to full power. Make a note of the
maximum RPM and the EGT. If your engine makes its rated power at
6000 RPM, you maximum static RPM should usually be a little less
than that. How much less really depends on how fast the aircraft
is because that max RPM will increase during flight. So if you
have a relatively slow aircraft with an engine that makes it's
rated power at 6000 RPM, you might expect to set your maximum
static RPM to 5800 or so. If you have an engine that makes it's
rated power at 6500 RPM, you might set your maximum static RPM
at 6300 or so. So if you are not close to that, you should make
a propeller pitch adjustment to load the engine properly. If you
do have to make a large change in propeller pitch, it will also
have an effect on your fuel-air mixture throughout the entire
RPM range of the engine. So if you were loaded to 6300 and had
to make it 5800, your mixture is going to get richer. If you
were loaded to 5800 and you need to change it to 6300, your
mixture is going to get leaner. So after adjusting your pitch,
it is a good idea to go through the carb adjustment process
again.
that may also be having an effect on your full power output.
Generally, you want the full power range to have a lower EGT
than the mid range for added protection under the higher stress
conditions, but if it is too much lower, the engine will not
perform. If your EGT seems to be very low at full power, and the
engine seems to bog down, you may need to change to a leaner
main jet. The main jet is the only part of the carburetor that
has control over the full power mixture. At full power, the jet
needle is all the way out of the jet and a needle adjustment
will not change this setting. The main jet, however, WILL have
some effect on the mid range mixture. So if you change to a
leaner main jet, it is always a good idea to change the needle
clip to the richest position on the needle for the first run up.
You can always make the mixture leaner in the mid range if its
too rich, but if it's too lean, you might need a new piston.
propeller loading effects mixture, this process is sort of like
hitting a moving target in some cases. If you find that you have
to make a large propeller adjustment, you may have to go back
and forth through this a couple of times. Once set, and set
properly, however, you should be able to enjoy many hours of
enjoyable, trouble free use. If you don't set the engine, carbs,
and propeller up properly, you will likely have many hours of
problems, frustration, and may even cause damage to the engine
and/or airframe.
on a customer's aircraft weather the engine is new or used. My
customers are usually very pleased with the results since they
no longer have to put up with the vibrations and throttle
response problems that they just took as normal before.
Hopefully you guys can get the same results.
Olenik Aviation - Supplying the lighter side of sport aviation.
Level III Repair Station for Rotax Aircraft Engines
Dealer for Summit Powered Parachutes
http://www.buyitsellitfixit.com
Toll Free: 877-AIR-MOTORS
Buy from a dealer who can support what they sell......
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