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by John Larsen
In the January issue I reported my experiences flying the adjustable
carburetor needles produced by Arctic Sparrow Aircraft Inc. in Anchorage
Alaska. Due to the large reader response to information about these
needles, we talked to the inventor, Mike Jacober of Arctic Sparrow. and
got some interesting follow-up information.
For those of you who did not read the earlier article, Jacober invented
a system where the needles of a slide carburetor may be raised or lowered
in flight by turning cables fixed to the needles. This allows the pilot to
lean the carburetors for high altitude or to enrich them again when the
EGT's say, 'ready".
When we contacted Mike, he said the needles can also be used to check
the accuracy of your EGTs. This was something I had not thought about-an
EGT reading can vary by a wide margin by where you place the probe
(thermocouple). This location is more sensitive on a 2 stroke than a 4
stroke engine because of the tuned exhaust pipe. Unless your manifold
carne predrilled, it is up to the builder to install the probe. This has
proved to be a problem because Rotax instructs us to place the ECIT probe
100 mm or 3.94 inches from the cylinder sleeve or the face of the piston
for 582 UL. The instructions sent with some kits had the dimension 3.94
inches from the cylinder. Measuring from the face of the cylinder mounting
flange, rather than the cylinder sleeve or piston face, places the EGTs
about 2 inches too far away from the cylinder, which in turn gives a
reading too high in temperature. Too high? Yes, because the probes can
read the temperature of both cylinders, not just the one intended. Did you
buy your engine used or were you in a hurry when vou installed the EGT
probes? (Heaven forbid, getting in a hurry to fly!)
To know where your EGT should read, Mike recommends you climb your
plane to a level cruise altitude and increase speed to your best cruise
speed, then richen the needles until the first hint of4-cycling can be
heard. This condition is so named because the engine only fires every
other revolution and sounds rough. At this point, turn the mixture control
knobs clockwise and the rpm of the engine will increase and the engine
will smooth out. Now look at your EGTs. Mark the gauge, as this is where
you want to adjust the needles to fly.
This method is more accurate than just trusting the EGT readings for
the reasons mentioned earlier. Also the
 ARCTIC SPARROW AIRCRAFT, INC. ASA Mixture Control for the Bing Carburetor Please use these instructions to purchase an ASA Mixture Control for the Bing 54 Slide Carburetor:
1. Package and ship the following parts:
Cover plate with a brass ferrule and lock nut .......part no 963-720
Spring cup............................................................part no 827-345
Carburetor piston.............(Slide)..........................part no 963-679
Stock jet needle (ex. 582 DC) without silencer.....part no 961-043
No modification will be made to the body of your carburetor.
You will receive all of the required parts and pieces with assembly instructions.
2. If you have a photo of your aircraft, please mail it to us also.3. Give us the Rotax or Hirth engine model number that uses the Bing 54 Slide Carburetor.
4. Send $109.95 for single carb assembly or $199.95 for dual (two) carbs, plus freight.
The turnaround time is usually 3 to 5 working days. (Excluding holidays)
Ship to:
Bud’s Ultralights / Authorized Dealer
5702 Ladd Lane
Anchorage, Alaska 99504
Ph. # (907) 333-2148
E-mail: bgish@alaska.net
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gauges will vary from unit to
unit.
My carburetors had the stock 272 needle jets and the ASA needles worked
just like they should, giving me 5 turns from rich to lean. If your carbs
do not seem to be giving you the fight EGT readings, you may need to
change the needle jet. To know where you need to be, run your engine to
4000 rpm and turn the needles counter clockwise as far as they will go.
This should give you a rich condition with the engine 4 cycling. Two turns
clockwise should give you a smooth running engine. If so, you are where
you want to be and the needle jet is correct. This puts you in the middle
of the 5 turn range. If you are rich or lean at this setting, you need to
go larger or smaller on the needle jetting.
How about the main jet? Your main jet will control your full throttle
performance and your engine needs to be jetted to a size that shows 500 to
750 cooler on the EGT's than your cruise setting.
Can you get into trouble with the needles? Mike has seen it happen with
an engine which has the propeller set at too high a pitch. Us old Rotax
flyers have watched the EGTs go from say 1050F on a steep climb to over
1250 F on a descent without us touching anything but the elevator stick.
This is because the engine is actually an air pump which turns itsself.
Each time the piston cycles, it pulls in a given amount of air. As the
slide is raised by increasing the throttle, the needle is raised and the
amount of fuel delivered is increased. Trouble comes with an over-pitched
prop as the fuel delivered went up but the rpm did not go up. More fuel
without more air equals a rich condition. The opposite is true when the
pitch is decreased, the rpm can go up without the slide delivering any
more fuel and now we may be running lean. If your propeller is pitched too
steep it will give a reading like the climbing engine-in both cases the
air-fuel ratio is such that the engine can get more fuel than air and the
EGT's will indicate low temperature. If you are flying in this condition,
and keep screwing the needles in (clockwise, trying to raise the
temperature) more than 5 turns, you can screw the needles right out the
bottom of the slides and the needles can drop into the carburetor
emulsifier tube, shutting off the engines mid range. If this happened in
flight, you can pull back on the adjustment knob and re-seat the needle in
the threads of the slide by turning the needle in a counter clockwise
direction.
The answer is not over-loading your engine with too high a prop
setting. Check this by static testing the engine on the ground to be sure
your engine can achieve the manufacturer's recommended rpm.
Mike claims there are over 400 installations of these needles in
everything from snowmobiles to air boats and this has produced hundreds of
happy customers. He has introduced a Tundra Trike with large wheels for
flying the rough country' in Alaska and it is getting good reviews. |
