Air Screw

[Allen Sutphin 705]

Someone refresh my memory, the air/fuel screw on a Bing 64 carb (912) is an air screw, turning it out leans the mixture and turning it in richens the mixture, Idle mixture of course.

[1avidflyer 1983]

That is correct. I think you want to start at 1 1/2 turns out.  JImChuk

[Allen Sutphin 705]

That is correct. I think you want to start at 1 1/2 turns out.  JImChuk

Got the intake issue solved, got the leak solved, but EGT's still a little warmer than I like from idle to mid-range. Going to check the E clip position next along with the idle jet. But things are slowly coming together. They are at 1 1/2 turns out now. Which should be correct according to the HKS manual.  But I've changed the intakes to shorter so could be a factor. CHT's are good so a little tweaking might be in order.

[nlappos 413]

I used this video for the basic setup of my carbs, and found it really helpful. https://youtu.be/PiZh1Ox1vmA

 

Allen , I am sure you know this, but for those who are looking to learn from these informative threads, here is the source material.

The thickness of the needle controls the mid-range mixture, with numbers 272, 274, etc used to control mixture in this area, see http://www.ultralightnews.ca/bing/rotax-bing-54-carburator-tuning-and-troubleshooting.html

 

Engine sputter or misfires (0 - 1/8 throttle)
This area is controlled by the low speed or idle jet, and air mixture screw. Check to make sure the jet is clean and the proper size. Check to see the air mixture screw is set correctly.

Engine sputter or misfires (1/8 - 1/2 throttle)
This generally indicates a lean fuel mixture. Check to make sure your needle and clip are in the right position and are not damaged. The air screw still has some effect here.

Engine sputter or misfires (1/2 - 3/4 throttle)
This area is controlled by the needle jet and jet needle. Verify that you have the correct jet and needle jet. Also verify that they are located BELOW the white plastic retaining cup. If they are located on top of the retainer the engine will run rough in all ranges, since the mixture is wrong in all locations.
The mid range is controlled by the needle and needle jet. The needle jets are available in various sizes with the larger numbers giving a richer fuel mixture and the lower numbers a leaner mixture.

 

Here are the various jet needles:

https://www.aircraftspruce.com/catalog/eppages/needlejetbing54.php

A reported problem with ALL Bing carbs is with failure of the jet and or needle clip. This can result in erratic running, lean fuel mixtures, engine returning to and idle during flight.

To determine whether you need to adjust the needle jets you require a EGT gauge and tachometer.
For example:
Many owners of 582's have reported high EGT readings in the 5600 to 5800 rpm range using the stock needle jet of 272 - using a 274 or 276 eliminates this problem.
Owners of older model 532 report having a problem keeping the engine set at 5400 rpm. It would jump up and down from 5400 to 5800 resulting from  a lean fuel mixture. Again the larger jet usually cures this problem.

Engine sputter or misfires (3/4 to full throttle)
This area is controlled by the main jet. Check to make sure it is in place and snug. Make sure there is no water in the bottom of the float bowl. Make sure the needle and clip are in good working condition. If the needle fails around the clip retaining area this will allow the needle to jump up and down causing erratic running. Proper float level is also important here to little fuel flow can cause an lean mixture while to must flow can result in a rich mixture.

Edited 10 Oct 2020 by nlappos

[1avidflyer 1983]

Good write up Nick.  I started to a day ago, and got writers cramp.  Lots of good info there on diagnosing where the problem lies.  JImChuk

[Allen Sutphin 705]

Yeah, I got my PH.D on Bing 54 carbs. The needle is a little more complicated to get just right due to many various configurations available.