Bing 64 Carburetor Disassembly and Explanation

Opening up the constant depression carbs from my Rotax 912. I take the time to explain how the various components of the carburetor function - constant depression, main metering, float level, idle system, bypass carburetor. talk, talk, talk.
Warning: I ain’t no A&P - view at your own risk.

[@darrylwbraun]

That was, hands down, the best explanation of a Bing carb I have ever watched! Thank you.

[@LightAndSportyGuy]

Thank you for the kind comment. I'm glad you found it interesting.

[@littlebittybert]

Old backyard mechanic here. I stumbled on this video while looking for some way to familiarize myself with the Bing carb on my 500cc Rotax powered MuZ motorcycle. I've cleaned out and refreshed dozens of carburetors over the decades. I've always had a fair grasp of how the things work, and I've had excellent luck making them run well in spite of my ignorance of the intricate details, but if someone asked me some specific questions about their function, I really didn't have precise answers. That's a little better now, thanks to your well done video. Thank you.

[@PeterClymans-n1l]

Very educative and clear clarification on the whole functionality, this helps to understand troubleshooting !

[@LightAndSportyGuy]

Thank you!

[@junker1223]

You have amazing communication skills!

[@LightAndSportyGuy]

Thank you!

[@steveevans5358]

Great job, very helpful, thank you for sharing.

[@LightAndSportyGuy]

Thank you for the comment. Glad you liked it.

[@DARisse-ji1yw]

Thanks for this. Planning to refresh my '85 BMW motorcycle. I think the same carbs as what you're demonstrating here. If not the same, very close.

[@LightAndSportyGuy]

Good Luck! And, thank you for the comment.

[@michaelc5378]

Thanks for the detailed video. I recently took mine apart but after reassembling the engine bogs down trying to go higher rpm. What could it be?

[@LightAndSportyGuy]

Assuming that it was fine before disassembly, it doesn't seem likely that varnish / debris is the problem. If the slide isn't lifting properly, that would make it run lean at high airflows - could the diaphragm have been damaged or not aligned correctly? Did you remove the needle from the slide? Correct C clip position - screwed down fully? Does it just bog for a moment then run OK? That would suggest accelerator pump issues.

[@nickr5658]

Thanks for making this video. I’m so frustrated with Rotax. Hardly anyone who knows these engines in the USA. Parts are crazy expensive and don’t get me started if you have an issue.

[@briand4000]

I hear ya. Just doing five year updates/replacements on my SLSA and the freakin' 912ULS is draining my wallet. Three hundred some bucks for diaphragms, bowl gaskets, some O rings and carb manifold coupler tubes. Lucky my floats are in spec (under 7 grams) or that would be another three hundred! Aviation is not for the average Joe on a budget.

[@nickr5658]

@@briand4000bing motorcycle carb parts. There not even airplane parts. Rotax puts their name on it and charges 10x cost. Now it’s an “airplane part.” Hope cont and lyc come out with a modern engine and put these turds out of business. Rotax has no respect for their customers

[@АндрейБаштовой-щ7в]

Great review, thank you. In the old Lycoming carbureted engines, the pilot can change the mixture quality from the cockpit, which can save a lot of fuel at cruise. Is this capability provided in the Rotax / Bing ?

[@LightAndSportyGuy]

No, there is no mixture control out of the factory on the carbureted Rotax. Some people have developed aftermarket devices, but I have no experience with them.

[@jamesfeuilherade3664]

Great video! I’m a bit familiar with SU carbs, but similar principles. Recently bought a Skyfox Gazelle with a Rotax 912A engine, Bing carbs. Seen Bings on BMW morocycles. Yes, carburetion of engines is a dark and clever art....! Very informative, learnt a bit about the idle circuit and I thought there was no altitude adjustment....constant velocity with that tapered needle might actually achieve slight leaning, up high in thinner less dense air.

[@metodyx7507]

Very good video, explained in detail! I have a question, would it be possible to drive the Himalayas, the highest mountain pass at 6200 meters, without additional adjustments on a BMW motorcycle (bmw r 100 rt) with such carburetors?

[@LightAndSportyGuy]

I really don't know. I've been up to about 3000 meters. Clearly the power would be greatly reduced - but beyond that, I would look for others who have driven vehicles over the pass - has anyone managed it without re-jetting the carburetor? Even vehicles other than one with the Bings?

[@metodyx7507]

@@LightAndSportyGuy I hope that someone else will read our correspondence and write their own experiences...

[@dwaynemcallister7231]

The red float Viton valve is a older part, a some point they changed to a black one with different spring tension and rubber formula, my engine from 1998 had the red one originally, many changes made to these Bing 64 including the starting carb (choke).

[@CraigKeenan-lp8tk]

I agree with the comment below, what's the small hole that's opposite the idle outlet hole on the vacuum side? (forward of the transfer ports and visible at about minute 29.33 on this video)

[@LightAndSportyGuy]

Not sure. Could be a second idle fuel port - there could be a cross drilling from the port I point to in the video. But, without a carb in my hand and the ability to blow air (or carb cleaner) into the idle mixture adjust I couldn't say for sure. It is odd that the hole for the port appears to be plugged with a screw instead of the more typical lead ball...

[@henryt2830]

Thank you for an excellent lecture on demystifying these cool looking carburetors. I am currently restoring a R75/5 and have sent away the carbs for a rebuild. After I re-assembled onto the bike, they work quite well, but once I have the engine warmed up, my idling is very high (over 2000rpm+). I have played with the idling mixture screw and the cable idling adjustment but it is still running high. Would you have an advice for me on where to look next? I realize it is a wide open question, but hoping you can point me to a right direction. Thank you.

[@LightAndSportyGuy]

Could it be the hard stop is not letting the throttle plates close even if the cables are slack - at 30:00 into the video you can see the hard stop screw to the right side of the screen - pointing down. I keep bumping into it as I play with the throttle. Another possibility is a vacuum leak that you have compensated for by opening the idle mixture enough to get it to run well (that seems less likely).

[@henryt2830]

@@LightAndSportyGuy Hi, today I have the bike a full tune up by changing out the plugs, contact points and reset the valves. The high idling is gone, but now I have an issue with idling way too low at full stop after the engine is warmed up. I also noticed that the plugs are really black covered with soot, I guess I had the jet mixture set way too rich. I'll try to fix the idle jet mixture again but the main problem now is the idling is way too low when I come to a full stop. If you have an idea, please let me know....thank you.

[@LightAndSportyGuy]

@@henryt2830 I suspect that fixing the mixture problem will help quite a bit. Speed could be low when you are hot due to just being too rich - well beyond best torque.

[@jupiterjohnson7191]

Question? Have you ever changed a Bing Carb ID plate?

[@LightAndSportyGuy]

No, I haven't.

[@azharc123]

Really good. Thanks so much.

[@LightAndSportyGuy]

Thank you for the comment!

[@bobbrown8615]

Well done video, I know you hate the record was not on, at one crucial part, I hate that too. On the altitude compensation bit, I'm not offering proof, just another's perspective, for your feedback. This quote from Rainbow Aviation seems to make sense to me: “. . . . (carb) senses the reduced atmospheric pressure on the lower half of the diaphragm, and the piston lowers in the body of the carburetor. This happens automatically even though the throttle valve position is still in the full open position. Because the piston is lowering the needle jet / jet needle restriction also automatically reduce the fuel to lean the mixture.” © Rainbow Aviation 2017 Carol and Brian Carpenter Could it be the the spring tension is constant, regardless of altitude, therefore it does have a reduced pressure on the lower half?

[@LightAndSportyGuy]

Could be - one of these days I'm just going to have to sit down and try to sort it out in my head.

[@bobbrown8615]

@@LightAndSportyGuy if you are anywhere near like me, my 'sorting out' days are waning.

[@LightAndSportyGuy]

@@bobbrown8615 🙂

[@johnb.6245]

Nice job.

[@cssira9532]

Thank you for this insight video on the bing carburetor. However I do not agree with you regarding the altitude compensation. To some extent, it does compensate. Higher altitude, lower density, less air. For constant pressure (or "suction"), the piston displacement will be reduced, does keeping the mixture ratio constant. Regards and congratulations again on the video!

[@LightAndSportyGuy]

Thank you for the comment. I may have to go back and do the math again, to compare the compensation with a fixed venturi... :-)

[@calc123]

Here’s how I think it’s altitude compensating: Bernoulli’s Equation P + pgh + (1/2)pv^2 = constant (little p is supposed to be rho, which is used for density) Setting up the equation for two points, one at the carburetor inlet and one in the Venturi, and doing a little manipulation, you will find that the pressure differential is equally to -(1/2)p(v1^2 - v2^2) (where v1 represents the velocity at the inlet and v2 the velocity in the Venturi). As is clearly evident, the pressure differential is directly proportional to the density of the fluid; the lower the density, the smaller the pressure differential. Being as the air on top of the diaphragm is vented to the Venturi, as altitude increases the pressure differential between the air on bottom of the diaphragm (atmoshperic pressure) and the air on top will become smaller. This results in the slide/piston sitting lower for a given throttle setting, which, by way of the jet needle, results in a leaner mixture. I’d love to hear your thoughts on this.

[@dwaynemcallister7231]

@@calc123 I have been told by a longtime expert on these Rotax that the Bing 64 will altitude compensate up to 3500' to 4000' alt. higher than this the mixture will get richer, some devices have been developed to adjust the mixture in flight, Green Sky Adventures sell a product and a French company has a digital system to monitor and adjust mixture.

[@lesizmor9079]

If they don't auto-compensate for altitude, how do your EGT's (exhaust gas temps) stay in their correct range as you fly from 1,000 feet to 10,000 feet? Without some way of leaning, mixture would go crazy rich. So yes, they do. Above 10,000 feet however, you are correct-- the carb doesn't compensate any more.

[@LightAndSportyGuy]

I have no idea what the EGT does with altitude. But I used to fly a Cessna 120 that came from the factory with the mixture wired to full rich on the Continental 85 - no problem climbing to 10,000 with that either - if you were patient. :-)

[@patrickplante8692]

Thanks for the video. Question - I have a 912 and under 3100 RPMs it wants to run real rough, but will idle ok at 1600 RPMs. We have pulled the idle jets on both carbs and cleaned them, they were completely plugged. Any others thoughts on what to check? thanks

[@LightAndSportyGuy]

Just off the top of my head (I'm hardly an expert on the Bings) - the rough running could be happening during the transition off the idle circuit - that's when the holes near the edge of the throttle plate come into play - if you had gunk in the carbs, it could be in that area as well. I think. Have you inspected the slide for smooth operation and metering needle for wear as another potential problem area?

[@patrickplante8692]

@@LightAndSportyGuy thanks for the information, we'll check those out. you're videos are very informative

[@MrHanowski]

@@LightAndSportyGuy I am working with Pat on this 912 repair. We pulled both air filters and verified smooth operation of the slide. Wondering about the air/fuel mixture screw and what RPM range it affects? You mentioned it is typically about 1.5 turns out, which is where we found it. What is the procedure for adjusting this with the engine running? Seems like you'd have to adjust both carbs together to determine proper setting. Perhaps a partner would make this job easier. How do you do it? Also, there is a large clear fuel filter that I can see some junk floating around in. But if it's running OK at low and high RPM, I am thinking it's not a fuel filter problem, but not sure. Another clue is that it seems to run better momentarily when the choke is applied, so it appears to want more gas (air/fuel screw adjustment needed?). Thanks for helping! As a Mechanical Engineer myself, I appreciated your thoughtful unbiased insights, attention to detail, and acknowledgement of the genius minds behind the design of this carburetor.

[@LightAndSportyGuy]

@@MrHanowski I have never done flow / tuning work on the Bing, so I can't really answer questions about exactly when the transitions between the idle / transition / mains happen. I adjusted the idle mixtures one at a time, that seemed to go OK. Just tweek the screw for best RPM. The left one was hard to get to with the engine running if I recall correctly. I would try the idle mixture to see how much difference it makes, but if the problem is off idle, that's likely to not cut it. My guess is that there is some gunk / varnish kicking around in that fuel system - has the airplane sat for a long time at some point? Had a boat that took a long time to get sorted - varnish kept coming free from the tank / fuel lines and clogging up the carb. Ethanol can do a number on the resin in composite fuel tanks as well - a possibility?

[@gyrocopterflyingclub6148]

Hi - can I ask is the Rotax 912 carb the same as a Bing Type 64?

[@LightAndSportyGuy]

Yes it is.

[@chrisarvin7531]

Roger from ctflyer forum said 10.5 is the way to set your float bracket

[@LightAndSportyGuy]

Thank you!

[@MrHanowski]

Jim, Do you "vacuum balance" your carbs on your 912 or 582? Wondering if that's necessary if one does a good job of mechanically "syncing" them. I'm fuzzy on the difference and why they are important. Thanks.

[@LightAndSportyGuy]

Mechanical sync is the first step - follow with vacuum balance. Very small changes in throttle plate angle cause significant differences in airflow near idle, so you are pretty much stuck with doing the vacuum balance to get it right. And, yes, I do the vacuum balance on my 912.

[@SafakSahin]

somehow i was led to believe that they were leaning with altitude

[@Bottleworksnet]

Because they do.