Bing 64 Idle screw adj

[procharger]

I read one place turning screw in makes it richer another place said turning it in makes it leaner.

Which is it?

[procharger]

Turning it out makes it leaner is my understanding.

[Tom Baker]

I don't know. I have always set them 1 1/2 turns out and left them there like I was taught. I've never felt that they needed changed from that setting.

[Roger Lee]

You don't need to mess with the air mixture screw.

Wrong terminology. 

You're talking about two different things here. The "idle screw" on top of the carb adjust idle rpm and turning it in makes the rpm go higher.

The "air mixture" screw on the bottom of the carb that should be turned out 1.5 turns. The black sooty plugs you see is from idling and uneven air flow to the cylinders from the air intake. The bottom plugs will also cause some of this because of the angle in the head makes them a tad less efficient vs the top plugs.

[procharger]

The Air Regulating Screw must be set as stated in the Bing Jet Chart in order to insure
smooth operation of the Idler Jet. This screw adjusts the air/fuel mixture at idle speeds
and for smooth acceleration. Turning the screw in a clockwise direction creates a richer
mixture while turning it counterclockwise creates a leaner mixture. To adjust this screw,
gently turn in a clockwise direction until the screw bottoms out, then loosen the screw (in
a counterclockwise direction) the number of turns as recommended in the Bing Jet Chart.
(effective range 1/2 to 2-1/2 turns out).
Use the carburetor piston Adjusting Screw to adjust the idle RPM. Turn this screw in
a counterclockwise direction until the Carburetor Piston is in the lowest position. Then
carefully turn the screw clockwise until it just engages the piston and then continue to turn it
clockwise for 2 to 2-1/2 turns. This determines the idle RPM. of the engine and should be set
at 2,000 RPM min.
Needle Jets/Jet Needles - The Jet Needle has three or four grooves which the

[Tom Baker]

From in person Rotax training I was taught to screw it all the way in, and back it out 1 1/2 turns for the 912 ULS. Unless something in the carbs is messed up, do this and you'll be good. I set idle RPM with the throttle cable when I balance the carbs. For the CT, unlike Roger I don't use the idle speed screw to make adjustments, I use the hard stop in the cabin. During balancing I have the idle speed screw backed off, and once the carbs are balanced I set a .004" gap between the stop and the screw. Again this is what I was taught in official training, and it has been working for me ever since.

[Roger Lee]

The hard stop in the cabin and the idle stop screw should hit at the same time. This is a Rotax teaching. If the throttle in the cabin is already all the way back how do you adjust the idle if you don't use the carb idle stop screw? How do you adjust the rpm up or down if the throttle in the cabin is all the way back. Carb syncs are very easy and quick once you learn how and why you do certain things. Like I said a carb sync only takes 5-15 minutes. The Flight Design's are the easiest to sync because of the throttle setup and small cable. Some planes are hard and never go back to the exact same place with the throttle because of the poor throttle design.

We cover carb sync in detail and perform live carb syncs during my class. If you take longer than 15 minutes to do a carb sync them you're either doing it wrong or have a carb issue you failed to identify. Usually by the next annual my clients carbs are usually only 0-2 inches of vacuum off.

[Tom Baker]

10 hours ago, Roger Lee said:

The hard stop in the cabin and the idle stop screw should hit at the same time. This is a Rotax teaching. If the throttle in the cabin is already all the way back how do you adjust the idle if you don't use the carb idle stop screw? How do you adjust the rpm up or down if the throttle in the cabin is all the way back. Carb syncs are very easy and quick once you learn how and why you do certain things. Like I said a carb sync only takes 5-15 minutes. The Flight Design's are the easiest to sync because of the throttle setup and small cable. Some planes are hard and never go back to the exact same place with the throttle because of the poor throttle design.

We cover carb sync in detail and perform live carb syncs during my class. If you take longer than 15 minutes to do a carb sync them you're either doing it wrong or have a carb issue you failed to identify. Usually by the next annual my clients carbs are usually only 0-2 inches of vacuum off.

That is not how I was taught in Rotax training. They were using a business card between the idle stop and idle speed screw. I picked up the .004" from Rotax documentation. I adjust speed and balance using the barrel that shortens or lengthens the cable. I look at the gauges and idle RPM to make adjustments. By looking at the split and RPM I know immediately which carb to adjust, and which way to adjust it. I also have a pretty good idea of how much adjustment needs to be made. 

I agree that Flight Designs are one of the easiest to balance. There are some airplanes that are a pain, and you have to use the idle stop and screw.

I also agree that that it doesn't take to long if you know what you are doing.

[FredG]

I don't have any formal Rotax training, although if you read what Roger learned from "Rotax teaching" and what Tom learned in "Rotax training" it is easy to wonder just what Rotax recommends.

My only guide is the Rotax 912 Installation Manual (the one published by Rotax) which shows a "feasible arrangement" for a throttle that has an adjustable stop that limits travel of the throttle lever for adjusting idle. Rotax also states that the "These stops have to be designed such to render adjustability and to prevent overload of the idle stop on the carburetor." (I may, or may not have the most recent version of the Installation Manual).

I installed an adjustable throttle stop in my ELSA CTsw so that I don't have to mess with throttle stop screws on the carbs or throttle cable adjusters (also on the carbs) to set the idle.  The adjustable stop is simple, effective, and fully compliant with the 912 installation manual.  

FWIW, RANS aircraft equipped with 912 engines do rely on the idle speed screws and the idle stop on the carburetor to adjust idle and have no mechanism to restrict the throttle position in the cockpit.  I have found the arrangement to be completely satisfactory, possibly making the whole discussion somewhat moot.

As always, confirm your installation with official Rotax documentation and not with my comments here (which are provided for your amusement only and not as a guide to aircraft maintenance).  

Edited March 30, 2023 by FredG

[procharger]

I would think if it wasn't so hard to get to, adjust the idle air screw while its

running to obtain best setting watching the RPM go up or down to

get the best or smoothest running engine you can, working on motorcycles

all my life that is how it was done forever. just saying. There was always a setting

to start with but for fine tuning you adjust idle air screw to get best running engine

possible. I here that setting at 1 1/2 turns is what most people do and it might be 

good enough but is it ideal. I don't know that answer. Not every carb. is the same

or perfect, depending on air filter, paper or K&N or dirty it might need some other 

setting. What do you guys think? You don't set weed eaters or blower type

engines that way you adjust till it runs like it should different engine same principle.

Trying to obtain perfect setting while its running. New carbs. most don't allow that

adjustment without some mods. to be able to adjust it. Buy an  aftermarket carb.

you can adjust high and low settings. Old saying I  have been doing it that way

for ever, my answer is maybe you have been doing it wrong forever. Good discussion

on this topic. Not saying anyone is doing this wrong just looking at different

ways to get to the best result. I had to open the adjustment on my CTLS a little

to get it to stop sooting plugs. It seemed to have helped a lot. I am at sea level.

[procharger]

 

 

Just as a side note when I worked on Honda bikes the CBX 1000 had six carbs. to set and

balance. What a pain in the butt.

[Tom Baker]

Something to think about. If the front plugs had soot, and the rear plugs were clean. Then you leaned to clean the front plugs. What did it do to the rear cylinders? Are they now to lean?

[procharger]

No it didn't change the clean plug much. Just helped the other one.

[procharger]

Roger do a video on carb sync

[Jim Meade]

Rotax Owner has such a video.  It's site worth the small subscription fee.

[Roger Lee]

Rotax class is today and tomorrow. I'll be teaching carb sync to 10 people tomorrow and it just happens to be on a CTLS.

[Madhatter]

Almost all certified aircraft with carburetors are adjusted for idle mixture while running.  But this is with one carb and not two with a balance tube. It can be a longer process than most think to get it right. If you adjust it right for a 95 degree day it won't be right for a 20 degree day in winter. I would rather be a little rich for idle than lean. I have seen engines quit on final at idle but with a non geared engine the prop keeps turning, one of the planes was hand prop only. I'm sure the soot occurs at idle and not in flight otherwise you would have a severely loaded plug.

[procharger]

Cal-Van Tools 482 90 Degree 1/4" Gearless Angle Drive, Chrome, One Size

I ordered one of these to try for the fun of it. Cool tool or a better figit toy 

check it out.