How The Constant Velocity Circuit Works

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How The Constant Velocity Circuit Works

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Brook's Airhead Garage

Күн бұрын

I demonstrate how the constant velocity circuit works on a Bing CV carburetor.

Пікірлер: 51

@twopheew9995 3 жыл бұрын

This guy is a great teacher!

@ACommenterOnYouTube Жыл бұрын

Well he explains it to where most would understand. Others will explain it and leave out details in hopes that YOU will fill in the missing blanks ... trust me those people are out there and have the nerve to attack YOU when you ask questions because they left out steps

@allegrofantasy 4 жыл бұрын

All your videos are really good

@LeonardLayne 11 ай бұрын

Thanks for responding

@froberts120046969 Жыл бұрын

Most correct detailed video I've seen yet. But! I have a question? I've watched your video part 1 and 2 at least 5 times now. I pulled the carburetor off and drilled plug out removed everything and cleaned real good. after putting it together it ran great. But, after taking it on a 10 mile run to fully warm up engine , it started spitting and dying at a stop. I had to idle it up to around 1150-1200 rpm's to keep it running. when I got home, i tried adjusting the mixture screw and it made no difference even if I ran in all the way in to seat. I have had this thing off 5 times now trying fix but can find a thing I did wrong. I even replaced the intake rubber boot to the carburetor. It was real hard getting the carb. unseated from the intake too. It Only does this after fully warmed up, when cold or warming up it runs perfect and even the turning the mixture screw changes but when it warmed up nothing! 2006 FXSTB night train with 17,000 miles. I sprayed carb cleaner around intake and other areas of carb and nothing. You have any ideas that I might try? I'm a 70 yrs old Vet and was a auto mechanic for over 45 yrs. I've rebuilt a lot of carbs back in the 70's and 80's but I lost on this one. Can you help

@BrooksAirheadGarage Жыл бұрын

froberts 12004, from what I could find doing a search on the Harley FXSTB model, it uses a constant velocity carburetor, but not a Bing carburetor, so I am not familiar with the details of that carburetor design.

@malcolmnash5850 3 жыл бұрын

Well explained Brook, Thanks again.

@BrooksAirheadGarage 3 жыл бұрын

You're welcome Malcolm.

@martij30 Жыл бұрын

Thanks for this explanation, very nice!

@BrooksAirheadGarage Жыл бұрын

You're welcome Martyboy Partyboy. 🙂

@cspark9186 Жыл бұрын

Excellent.

@BrooksAirheadGarage Жыл бұрын

You're welcome CS Park. :-)

@lylew9 6 жыл бұрын

Excellent description. Thank you.

@michelp1398 Жыл бұрын

Great video Brook, thanks!

@BrooksAirheadGarage Жыл бұрын

You're welcome Michel

@steveavant9727 7 жыл бұрын

Well done, thank you.

@samcoder6900 Жыл бұрын

Wait a minute Brook, isn't the purpose of the throttle lever in the cockpit to change the force of depression at the site of the carburettor ? If we have a "constant depression" system, why does my manifold pressure indicator indicate different values as I set different power settings with the throttle lever ? 🤔 Edit to (possibly) answer my own question: When we say 'constant depression' we're only talking of the static pressure in the Venturi, which stays constant in this type of carburetor no matter the position of the throttle lever. The pressure outside the Venturi in the air intake circuit remains different at different throttle settings hence the Manifold Pressure indicator indicating different readings.

@BrooksAirheadGarage Жыл бұрын

Sam, as the throttle plate opens, more vacuum exists in the carburetor passage, so more air flows. As more air flows, the pressure at the center of the venturi drops. The passage in the carb body that goes to the top of the diaphragm reduces pressure on the top and that pulls the slide up allowing more air to flow through the carb and the needle to move up in main jet allowing more fuel to enter. The constant depression ensures the volume of air flowing through the carb matches the fuel flow so the air/fuel mixture is correct, even if the atmospheric pressure is lower due to higher altitudes. This means the carbs are not too rich with a fairly large change in altitude.

@ACommenterOnYouTube Жыл бұрын

I had 2 small 49cc bikes and the throttle cable was directly mounted to the top of the carb & pulled the main needle jet up and down directly ... My Suzuki S40 is NOT like that. Its this design here and when i had to pull it off to clean the idle jet, i saw that the throttle cable ONLY turned the throttle plate and i was like ... 🤔 ... so how does the main needle jet go up and down based on throttle ... ?? Well you just answered my question 👍🏾

@shaneking6140 3 жыл бұрын

thank you great explanation

@BrooksAirheadGarage 3 жыл бұрын

You're welcome Shane.

@LeonardLayne 11 ай бұрын

Have a question. When aircraft is parked in hanger which position should I leave throttle open or closed?

@BrooksAirheadGarage 11 ай бұрын

I have no idea.

@peterrose7329 8 ай бұрын

What would happen if you slightly enlarged the two holes at the bottom of the slide ?

@BrooksAirheadGarage 8 ай бұрын

Pete, I have no idea. I believe they create the vacuum above the diaphragm as they are aligned with the venturi

@59jaguar 4 жыл бұрын

Excellent explanation. I am wondering if there are any changes to carb functioning when the air box is removed in lieu of adding air filters to each carb instead?

@BrooksAirheadGarage 4 жыл бұрын

Hi Rodger, Yes, removing the BMW designed airbox changes the air flow through the carburetor. From what I've heard, BMW designed the airbox (the later one used on this bike is even better than the original "clam shell" airbox) to provide optimum carburetor performance. Removing the airbox, or bypassing it, to use pod filters, K&N for example, does not make the engine run better (more HP and torque). The goal of the airbox is to slow down the inrush of air into the carburetor intake to as low a velocity as possible. It's the pressure difference between the high pressure carburetor inlet and low pressure outlet that is important. Since moving air has lower pressure than stagnant air and you want the highest air pressure you can get on the inlet side of the carburetor, pod filters are not helpful. They can't slow the inrush of air across the RPM range so the pressure difference across the carburetor is reduced. That disrupts the ability of the carburetor to provide the correct fuel/air mixture across the RPM range.

@59jaguar 4 жыл бұрын

Brook's Airhead Garage , that sounds correct. It always amazes me how others in their shop try to improve upon this engineering , most cafe racer type bikes appear more for show than improving real performance it seems. Thanks again for your insight . One last question would be how often do these bing carbs need to be rebuilt ? Cheers

@BrooksAirheadGarage 4 жыл бұрын

Hi Rodger, a good question with a "depends" answer. It you drain the float bowls for the winter the o-rings last longer, and the internal passages don't get deposits, than if they sit for months in fuel laced with ethanol. As a rough rule of thumb, I'd suggest 5-7 years. That said, if the bike isn't running well after a tune up, you can pull the main jet stack and the idle fuel adjustment screw to inspect the o-rings. If they are showing deterioration, assume all the o-rings, including the one on the throttle shaft, need to be replaced. I hope that helps.

@GarethKing1 3 жыл бұрын

If the opening and closing of the throttle can manage the amount of air entering the engine, what is the purpose of the slide?

@BrooksAirheadGarage 3 жыл бұрын

It regulates the amount of air that flows in the venturi. This in turn adjusts for altitude change so the correct fuel-air mixture is achieved as air density decreases with altitude.

@GarethKing1 3 жыл бұрын

@@BrooksAirheadGarage thank you

@Triumphandme 4 жыл бұрын

Hi great video many thanks does adding a spring to the slide make a lot of difference my R75/5 has a spring in each slide? Regards Al

@BrooksAirheadGarage 4 жыл бұрын

AL: It seemed to smooth the transition from idle to mid-range after I did it.

@Triumphandme 4 жыл бұрын

Brook's Airhead Garage that’s true for me too. I will test it more when we can ride again. Great video thanks for the time you have taken. I understand the carbs far better now. Regards from the UK.

@albertcosta5755 3 жыл бұрын

Hi Brook! One question about this carburetor system ... My left carburetor (Bing 32 - R80G/S) is making me crazy. After a 'long' trip, (Transpyrenees) and after always working super good. It is working strange. I need to help the carburetor to go down rpm by braking with the engine. I mean engine goes down rpm normal, but this carburetor stays a over the ralenti rpm when I stop like in a trafic light. Like the double of normal rpm.... I have changed gaskets, round rubber in ring mixing screw. Also rechecked mixting. Only left carburetor, after 10/12 minutes driving (engine good temp) Any help????? What I am missing???? THANK YOU VERY, VERY MUCH IN ADVANCE!!!!!

@BrooksAirheadGarage 3 жыл бұрын

Hi Albert. I would check the diaphragm for a tear or a hole. I would verify that the slide moves smoothly in the bore. One way to do that is to remove the air intake plastic pipe from the air cleaner on both carburetors. Rev up the engine and then close the throttle and verify that both slides come down to the same level. I would also verify that the throttle cable. It may have a kink or a wire in the cable maybe broken preventing the inner cable from moving smoothly inside the outer cable which would keep the butterfly open.

@albertcosta5755 3 жыл бұрын

@@BrooksAirheadGarage Thanks a lot Brook!!!! I will check everything you said!!!

@albertcosta5755 3 жыл бұрын

FINALLY SOLVED!!! YEEEEEEAAAHHHH!! Do you know what it was.....???? The two valves of the left cylinder, the cylinder that the carburetor wasn't working properly. were too closed. I bought the typical thing to mesure spaces in between pieces (Mesure like 0,05 mm, 0,10mm, 0,15mm, 0,20mm, etc) And just adjusted exhaust valve 0,20mm and admision valve 0,15mm. And now engine goes again to normal ralenti rpm when I brake the bike ..... So, this cylinder coudn't close correctly the valves, so it didn't do correct vacum to the carburetor to work correctly. HAPPY!!!

@BrooksAirheadGarage 3 жыл бұрын

@@albertcosta5755 I'm glad to hear you found the problem. But, you should check the valve clearance on the left cylinder again in 1000 miles (1,600 KM) and see if they are closing up. Exhaust valve seats on 1970-1987 airheads can be damaged by no lead gasoline. If the valve clearance is closing up in 1,600 KM, it's time to have your heads rebuilt to prevent a broken valve.

@albertcosta5755 3 жыл бұрын

@@BrooksAirheadGarage Thank you Brook!!! I will do this in 1000 miles as you say! I didn't know!! I am amateur.... Thank you again for your help and info!!!

@chrisdavis7433 Жыл бұрын

My bing 54 has nothing like this it’s more like a small piston

@BrooksAirheadGarage Жыл бұрын

It’s not a constant velocity design carburetor.

@kgucmen 3 жыл бұрын

That carburator has probably more IQ and definitely more knowledge about fluid mechanics in its body, than the chemical engineer, I am....

@BrooksAirheadGarage 3 жыл бұрын

Kaya, Indeed, the ability to control the metering of fuel, atomization, and mixing with air in the correct amounts across a large range of atmospheric pressure is amazing. I suspect the non-compressible fluid flow equations got the designers part way there, and then testing fine tuned the dimensions of the passages to achieve the final result. When you think of the slide with the needle, you had to account for friction and the compliance of the diaphragm to get the movement of the slide to work correctly with those small forces.

@garethedwards3725 5 жыл бұрын

@grundejerforeningenptstran7654 3 жыл бұрын

@loveplanes Жыл бұрын

I think you helped me to find a problem I have. Suddenly my engine, at full throttle, is giving me less RPM of what it normally does. Please, need ideas!!!!. Thanks!

@loveplanes Жыл бұрын

Thanks for sharing! How you clean it?

@BrooksAirheadGarage Жыл бұрын

I show that here: brook.reams.me/bmw-motorcycle-rebuilds/1973-bmw-r755-rebuild-project/bmw-r75-5-bing-carburetor-rebuild/

@loveplanes Жыл бұрын

@@BrooksAirheadGarage thanks a lot! Very good information…