Bing carb mixture control part 2 - by Arctic Sparrow.

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More Bing carburator needle news Part II

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

asa5.gif (2545 bytes)ARCTIC SPARROW AIRCRAFT, INC. ASA Mixture Control for the Bing Carburetorasa4.gif (9050 bytes)

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 961-043bg1.jpg (14817 bytes)

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:

Budís Ultralights / Authorized Dealer
5702 Ladd Lane
Anchorage, Alaska 99504
Ph. # (907) 333-2148
E-mail: bgish@alaska.net

 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.

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