How The Idle Circuit Works

[@clarkmorris3312]

I really wish we had videos of this quality back when I started working on BMW motorcycles. You are doing a great service by helping keep these wonderful bikes alive and help keep the fun in working on them. There is no way I would be able to keep my bikes without being able to work on it myself. Thank you for taking the time to do your web site and videos to help all us owners. ABC #4099.

[@BrooksAirheadGarage]

Hi Clark, Thank you for the kind words. And best of success keeping your airhead flying.

[@danielng1999]

Thank you very much for sharing this valuable information. I have a 200cc using PZ 27 carburetor and it constantly pops in the air cleaner and shuts down during in idle mode. After watching your video I understand how a carburetor works and I cleaned the idle circuit this morning after that my motor started without choke and popping in the air cleaner is gone. Thank you again. From Kuala Lumpur, Malaysia.

[@yamidgaray9074]

thank you for taking the time, making this video.

[@BrooksAirheadGarage]

You're welcome Yamid.

[@chrisfist2042]

I have had a basic understanding of what a venturi does for a long time but this is and the other videos you have about constant velocity carbs have truly expanded my understanding of how carbs work, thank you!

[@BrooksAirheadGarage]

Thank you Chris. I too only had the basics and then I did a deep dive into the design to understand more about how these are made and how they work.

[@stevekwall925]

You are a excellent instructor on these Motorcycles, You remind me of my FTD Instructors when I was in the Air Force learning Jet Engines .

[@BrooksAirheadGarage]

You're welcome Steve. It's good to know the explanation makes sense.

[@sammytabrizii3069]

I dont know much about engines and understood everything , great lecture !

[@BrooksAirheadGarage]

Thank you Sammy. I’m pleased my explanation was understandable.

[@jrc58526]

Thanks for a really detailed and understandable explanation

[@BrooksAirheadGarage]

You're welcome John. Thank you for stopping by.

[@foesfly3047]

I just studied all your videos explaining Bing CV Carb operations. They are Excellent. My model 94/40 is on a Jabiru aircraft engine and has had issues with very rich idle ever since I bought the plane from previous owner. I now believe I've discovered its main housing is defective. Besides the idle fuel port that provides fuel as metered through the idle mixture screw, mine has 2 tiny holes that deliver fuel into carb throat that comes after the Idle Jet but is not metered by the mixture screw. I have to be cautious as to possible design differences between the motorcycle and aircraft applications but so far, it seems highly likely this is a flaw in the 1 I have and is the reason for my rough idle and black exhaust smoke (unaffected by idle-jet and mixture screw changes). Thank you for the education.

[@BrooksAirheadGarage]

Hi FoesFlyDennis, I hope you get to the bottom of your issue. There are certainly differences between the aircraft and motorcycle BING carburetors. I've no knowledge about the aircraft versions, so I'm not able to help you out.

[@skii_two]

I've been having some problems with my snowmobile getting out from idle. It quickly bogs out, but accelerates after about 2 second of revving. I've been told It's an idle circuit problem most likely, and this really helped me understand it. I've also been told it might be an accelerator pump issue, so I'll have to look into it further. Great video!

[@quinnsmithy8778]

very comprehansive and clear video, thank you!

[@BrooksAirheadGarage]

You're welcome Quinn

[@ickster9709]

Working on a different carb, but it's also a CV and this finally helped me understand how the idle circuit works. Hopefully I'll be able to sort out the lean problem I'm having at idle. Thanks!

[@furleybart]

Finally, somebody knows what they're talking about....great video:)

[@BrooksAirheadGarage]

You're welcome Bart

[@johanwithag2432]

Thanks for this clear explanation. I was looking for this already for a long time.

[@BrooksAirheadGarage]

I'm glad this was helpful for you. 🙂

[@timwilkson7637]

A great and very clear explanation -thank you very much Sir!

[@BrooksAirheadGarage]

You're welcome Tim. Thank you for visiting.

[@schwedenburger]

Thanks for this really good explanation

[@BrooksAirheadGarage]

you're welcome 🙂

[@imnotgivingmy_name_toamach7491]

beautiful explanation - thank you

[@BrooksAirheadGarage]

Imnotgivinymy_name_toamachine: You're welcome and thank you for stopping by,

[@tahep3906]

thanks for this great explanation on idling...

[@malcolmnash5850]

Brilliant explanation, thanks very much.

[@BrooksAirheadGarage]

You're welcom Malcolm. Thanks for stopping by.

[@subhash0308]

Superb explanation

[@BrooksAirheadGarage]

You’re welcome S N. I’m pleased it was helpful to you.

[@stevekwall925]

When you adjust idle speed do you adjust the cable that controls the butterfly or would you adjust it using the adjustment screw ?

[@BrooksAirheadGarage]

Steve, you use both the throttle cable and the idle mixture screw to adjust the idle. Here is one way to do it: kzbin.info/www/bejne/a5PQe2OfjqeMnbM

[@stevekwall925]

Thanks Brooks your the greatest

[@keithnicholl3859]

Hi...great video. I've just rebuilt a 1983 r65 with 32mm bings My problem is that on cold start...the plugs both stay bone dry...with no signs of fuel. After watching your video...I'm going to blow air thru the idle jet to see if the passages that you pointed out are clear.... Hopefully that may fix it Thank you

[@BrooksAirheadGarage]

Keith, I hope that works out.

[@keithnicholl3859]

@@BrooksAirheadGarage It did thanks

[@fyreblade1262]

you're amazing. Thanks so much for the explanation

[@BrooksAirheadGarage]

You're welcome. 🙂

[@maithem212]

Very well done sir, thank you.

[@BrooksAirheadGarage]

You're welcome. 🙂

[@F1Hopeful]

Wonderful!!!!!! Thank you sir!!

[@panagoskakatosis5314]

my xtz 750 start with 800 prm then need to wait be hot the engine ..if i change this start jet be more biger nuber will be start more than 800 prm.. ????? or need also the main jet biger nuber from 70 to 72 for exaple??

[@BrooksAirheadGarage]

Panagos, I adjust the throttle plate stop screw to raise the RPM then adjust the idle mixture to get the highest RPM at that throttle stop screw setting. Changing jets is not necessary unless the engine is running too lean or too rich at idle. The main jet does not influence the idle circuit. Look at the other videos I posted that explain how the other carburetor circuits work for more details.

[@en8581]

Thanks- I never understood this till now! Is this true for all 2 strokes, eg outboards, weed trimmer, blower, etc?

[@BrooksAirheadGarage]

E N, No. It's only true for this model Bing carbuetor.

[@en8581]

Thanks for responding so quickly- just to clarify I was wondering if the general principle is the same, not the exact location of the orifices. I have another question I am sure many others wonder about: why do some motors have the needle valve that opens up main jet area vs other motors (eg my yamaha outboards) only use the Venturi effect with more air flow to increase fuel flowing? In other words, what is the advantage of a carb with the needle that goes in and out to control fuel flow through the main jet? Thanks!

[@BrooksAirheadGarage]

@@en8581 I have no experience with yamaha outboard carburetors. In every carburetor, the amount of fuel has to be metered as engine speed changes. BINGS use a needle and needle jet to adjust fuel in the mid range for more precise control. That said, a motorcycle engine runs across a wide range of engine speeds most of the time. Boat engines are more like airplanes in that they tend to run at a constant throttle more. That maybe why precise mid-range metering of fuel isn't as critical. That is entirely speculation on my parts because as I said I have no experience with boat carburetors.

[@josepeixoto3384]

been a fewv hours,still did not find how the pilot circuit works(transition bt idle ,and full,with the small (pump?,diaphragm?).

[@Lachielloco]

GREAT VIDEO STILL IN 2022.

[@alfonsojurado2565]

Awesome video Brook!! How do you get the carb body to look so clean and bright??

[@BrooksAirheadGarage]

Hi Alfonso, Here is link to one of the documents on my web site that shows the techniques I use to refinish various parts on these rebuild projects: --> brook.reams.me/bmw-motorcycle-rebuilds/1973-bmw-r755-rebuild-project/51-bmw-r755-refinishing-techniques/ The secret is lots of elbow grease and patience.

[@alfonsojurado2565]

Brook's Airhead Garage thanks! Very helpful!

[@allegrofantasy]

Very well explained. Tx

[@johnmccormick9042]

This is very interesting. I have an '86 R-80 Do those carburetors work the same way.

[@BrooksAirheadGarage]

John, Yes they do as that bike has the constant velocity Bing Carburetor (64/32/375 & 358). The model is different, but the operating principles are the same. Best. Brook.

[@BrooksAirheadGarage]

Yes,

[@tumeloketso7033]

what kind of a carburetor is this?

[@BrooksAirheadGarage]

Hi Tumelo, it's A BING constant velocity, as I mention at 5 seconds into the video clip.

[@khalilbrahim7472]

سلام كيف الاتصال بيك

[@foreverwood1963]

Good explanation

[@BrooksAirheadGarage]

Thanks. I'm glad it made sense and was helpful.

[@daveco1270]

Makes sense. I understand how the carb works when you give it gas, but I wasn't sure exactly how it worked at idle. Now I know.

[@BrooksAirheadGarage]

Hi Dave7777, Great. It took a bit of research for me to fully understand that the "enricher", aka, choke, is actually a tiny carburetor of it's own.

[@burtlade1705]

OK, that all made sense. Thanks.

[@toncisiskovR51-3]

Hvala pozdrav iz Hrvatske .

[@BrooksAirheadGarage]

Bio sam u Hrvatskoj na motociklističkoj turneji i volim vašu zemlju :-)

[@toncisiskovR51-3]

@@BrooksAirheadGarage koji je vaš e-mail ?

[@toncisiskovR51-3]

@@BrooksAirheadGarage pozdrav , gledam vaše videozapise i učim , veliko hvala .

[@A23Beech]

I watched all your videos, and they are a great help for the rebuild project of my r100rs. Your carburetor looking so nice and shiny, how did you achieve that? Thanks from a great fan of your videos.

[@BrooksAirheadGarage]

Hi A23Beech, I show how I refinish parts, including carburetors, on my web site in this document: --> brook.reams.me/bmw-motorcycle-rebuilds/1973-bmw-r755-rebuild-project/51-bmw-r755-refinishing-techniques/ I wish you great success on your rebuild project.

[@madmarkstoys]

SWEET JOB!!

[@flobeeonekinobee2353]

If it doesn't work is it an idle bastard?

[@wingson8951]

2 weer