1971 Airhead R75/5 help

[bigvic54]

… on the outlet (engine) side of the carb, there is a drilled & plugged passage through the aft wall of the Idle Mixture screw bore; and the other micro hole, that the needle end of the Idle Mixture screw engages, is drilled into the floor. These are the two ports for the fuel mixture, shown in #17 above.

View attachment 97129

I appreciate all the work you're putting into trying to help me.

I notice you carb is a 64/32/9 R and mine doesn't have the R. Does that indicate left and right? Mine looks the same as yours.

I have the plugs in the same places that yours' has. The question is, do I want to drill them. I have to say it seems to be a little intimidating. My first thought is to try heat. I read that the varnish that forms in the lines melts at 130 degrees. I'm wondering if I could heat the body and clear the passage with carb cleaner without starting my head on fire.

Now, the question on how to insure the passages from the carb inlet; thru the Idle Mixture Jet; out the micro hole in the floor of the outlet, are clear ? Gotta think on this a bit but, I believe it must be done, backwards ?

 

[20774]

I must have missed something...why is there a consideration for drilling plugs or passageways? That seems like a destructive effort and no coming back from that. If I couldn't get the carbs to work using the typical adjustment methods, then I'd be thinking about contacting Bing and maybe even sending them the carbs to be sure everything was in spec.

 

[bigvic54]

I must have missed something...why is there a consideration for drilling plugs or passageways? That seems like a destructive effort and no coming back from that. If I couldn't get the carbs to work using the typical adjustment methods, then I'd be thinking about contacting Bing and maybe even sending them the carbs to be sure everything was in spec.

The issue is that there is a blockage between the stand pipe and the idle adjustment screw that doesn't allow fuel through. I'm trying to clear the blockage using different carb cleaners and haven't been able to insert anything into the line. As I understand it, the plugs are there to allow access.

I spoke with Bing and I know I can send the carbs there. I've done business with them before. I'm trying to save money.

 

[20774]

Did you discuss the blockage with Bing? Any thoughts from them? OK. I'm not there and haven't gone through what you are dealing with. But I can't say as I've heard about drilling things out before. Just kinda foreign to me. Good luck!!

 

[bigvic54]

Did you discuss the blockage with Bing? Any thoughts from them? OK. I'm not there and haven't gone through what you are dealing with. But I can't say as I've heard about drilling things out before. Just kinda foreign to me. Good luck!!

Thanks

 

[olironrider]

The issue is that there is a blockage between the stand pipe and the idle adjustment screw that doesn't allow fuel through. I'm trying to clear the blockage using different carb cleaners and haven't been able to insert anything into the line. As I understand it, the plugs are there to allow access.

I spoke with Bing and I know I can send the carbs there. I've done business with them before. I'm trying to save money.

First, a Mea Culpa: I keep rolling my carb body round-n-round, thinking of your situation. It dawned on me (yup, a Senior Moment) that, the brass Stand-pipe is the fuel source to the Starting Enricher ! The red in the following picture is the fuel flow from Stand-pipe to Enricher Valve; blue is the inlet airflow thru the enricher cover to the various ports of the Enricher Valve; the green is fuel/air mixture which flows to the diagonal port on the side of the outlet to the engine…




All the fuel for the idle circuit is drawn from the float bowl.

Now, I’m thinking that the idle fuel passages from the Idle Jet, get smaller and smaller in diameter going to the micro hole and outlet into the airflow going into the engine. The micro hole needs to “back-flushed” towards the Idle Jet ?

The bore for the Idle Mixture Adjuster, has to be blocked off by fully seating the adjuster. We know that screw connects to the fuel/air mix from the Idle Jet. The Metering Orifice in the rim of the inlet air coming in the carb, must be blocked off also; maybe a wooden toothpick firmly placed in the orifice ?

With the blockings in place, the only openings in the short section of factory drilled & plugged passage are, between the Idle Mixture Jet bore and… the other micro hole in the floor of the outlet (engine) side of the carb.

As you’ve seen with my carb body (I’ve no idea what the “R” means as, a 64/32/9 is the left carb, fueling the #1 cylinder; 64/32/10 fuels the right, #2 cylinder) is completely stripped.

I’m thinking of a necked-down air nozzle; maybe with a small (1/4”) copper pipe elbow, supplied with 100-120 PSI shop air; fitted inside the outlet of the carb directly upon the micro hole… might just force a clog backwards into and out the Idle Jet ?

Shee-it, even fill the Idle Jet bore with a “magic elixir” again and repeatedly, apply shop air to the micro hole and Idle Jet bore.

To clear some things up: the “as cast” carburetor bodies are identical; they get “sexed” to the appropriate left or right side during machining. Fuel/air passages/orifices are drilled as they would be impossible to “cast in”. Drilling completed, plugs or balls are pressed/glued in the appropriate locations, to make them functional.

I would not even dare to put one under my INDEX vertical milling machine and drill them out ! The size of the bits required; different materials; accurate positioning requirements… is a Fool’s Task.

Hope this make sense…

 

[bigvic54]

First, a Mea Culpa: I keep rolling my carb body round-n-round, thinking of your situation. It dawned on me (yup, a Senior Moment) that, the brass Stand-pipe is the fuel source to the Starting Enricher ! The red in the following picture is the fuel flow from Stand-pipe to Enricher Valve; blue is the inlet airflow thru the enricher cover to the various ports of the Enricher Valve; the green is fuel/air mixture which flows to the diagonal port on the side of the outlet to the engine…


View attachment 97131

Now, I’m thinking that the idle fuel passages from the Idle Jet, get smaller and smaller in diameter going to the micro hole and outlet into the airflow going into the engine. The micro hole needs to “back-flushed” towards the Idle Jet ?

The bore for the Idle Mixture Adjuster, has to be blocked off by fully seating the adjuster. We know that screw connects to the fuel/air mix from the Idle Jet. The Metering Orifice in the rim of the inlet air coming in the carb, must be blocked off also; maybe a wooden toothpick firmly placed in the orifice ?

With the blockings in place, the only openings in the short section of factory drilled & plugged passage are, between the Idle Mixture Jet bore and… the other micro hole in the floor of the outlet (engine) side of the carb.

As you’ve seen with my carb body (I’ve no idea what the “R” means as, a 64/32/9 is the left carb, fueling the #1 cylinder; 64/32/10 fuels the right, #2 cylinder) is completely stripped.

I’m thinking of a necked-down air nozzle; maybe with a small (1/4”) copper pipe elbow, supplied with 100-120 PSI shop; fitted inside the outlet of the carb directly upon the micro hole… might just force a clog backwards into and out the Idle Jet ?

Shee-it, even fill the Idle Jet bore with a “magic elixir” again and repeatedly, apply shop air to the micro hole and Idle Jet bore.

To clear some things up: the “as cast” carburetor bodies are identical; they get “sexed” to the appropriate left or right side during machining. Fuel/air passages/orifices are drilled as they would be impossible to “cast in”. Drilling completed, plugs or balls are pressed/glued in the appropriate locations, to make them functional.

I would not even dare to put one under my INDEX vertical milling machine and drill them out ! The size of the bits required; different materials; accurate positioning requirements… is a Fool’s Task.

Hope this make sense…

Once again I agree with everything you said and thank you for saying it.

I haven't found a "magic elixir" that works, and I've tried a few. I've tried air, I have a compressor, with no results. I tried heat. It was hot enough that when I poured a bit of water on it the water boiled, no results. I'm not going to drill.

I'll pack it up and mail it to Bing and hope its not an arm and leg but, what choice do I have? No one said this hobby was cheap.

 

[guenner]

bigvic54, you said before:

"I agree with you that its a fuel supply issue but only on the idle."

And the idle only works when you continue spraying carb cleaner in after the motor was running off idle?

 

[olironrider]

Once again I agree with everything you said and thank you for saying it.

I haven't found a "magic elixir" that works, and I've tried a few. I've tried air, I have a compressor, with no results. I tried heat. It was hot enough that when I poured a bit of water on it the water boiled, no results. I'm not going to drill.

I'll pack it up and mail it to Bing and hope its not an arm and leg but, what choice do I have? No one said this hobby was cheap.

Before you do anything rash

I just tested my theory of fully turning the Idle Mixture screw in; putting a round toothpick in the air inlet orifice; filled the Idle Mixture Jet bore with 10W oil; seated my rubber tipped blow-off nozzle in the Idle Mixture Jet bore; put 100PSI shop air to it and… EUREKA !!!

Only the micro hole to the inlet side of the Throttle Plate, farted a nice spray of 10W oil

From inlet orifice to idle jet bore to the micro holes on the outlet, the passages flow as intended !

Thinking of the “scientific method” of troubleshooting, I would happily send you my bare-naked 64/32/9 carb body; you swap-out all your components to it (hopefully, you used Loctite to retain the throttle plate screws); install it on the /5 and… try it !

We will then know if your carb is blocked in that area ?

If so, send your carb body to BING (the namesake is Berthold Bing) for certain resolution. Perhaps, ride my carb a bit then, when your carb body returns, swap the parts out and send my “lab rat” carb body back !

FWIW…

 

[oldcamper]

I have never owned a 1971 R75, and have no real experience working these specific carbs, but are these the “infamous” R75 Bings that gave everyone so much grief in the ‘70’s when they were new? I seem to remember many riders giving up and converting to Mikunis back then. Carbs are a lot cheaper these days. I see eBay has Mikuni clones for $50 or so. Are these early Bings even worth fixing, given the cost of Bing parts and the likelihood of success?

 

[20774]

Snowbum discusses the early Bing CVs here:

EARLY R75/5 BMW motorcycle Bing CV carburetor, 64/32/1; 64/32/2; 64/32/3; 64/32/4; 64/32/9; 64/32/10

Bing CV carburetors, BMW airhead /5, slash 5, R75/5

bmwmotorcycletech.info

The problem numbers were /1/2/3/4 as I recall. They were "crude" he says. They work but they're just finicky.

 

[olironrider]

Hello “bigvic54” !

It’s coming up on a month since you were opting to send that recalcitrant BING 64/32/9 to the BING Agency, for evaluation and remediation.

What did you do and, what was the outcome ?

Just like the “NATIONAL ENQUIRER… Inquiring Minds Want to Know !”, of year’s ago ? It’d be more information available in the, “Pool of Knowledge” for future generations

 

[olironrider]

Kurt… seeing you mention “Snowbum” and his definition of the early BING Carburetors as, “crude”; here’s an image of my original 1970, Sales Brochure - R 50/5 R 60/5 R 75/5 front cover, with what appears to be “sand-cast”, like in agricultural implements, 64/32/X carbs…



… even my 1949 Farmall CUB has better looking castings

Further, to test the commitment of us Motorraders to the marque, BMWAG installed “EVERBEST” petcocks !

 

[20774]

Rough castings have more surface area to help dissipate heat. Maybe!

 

[olironrider]

… right downstream of combustion chambers ? Probably same flawed logic of inline, air-cooled, V-twin cylinder configurations !

But wait ! Those of us that have an Aviation background, particularly with reciprocating piston, carbureted, air-cooled engines, know of Carburetor Icing !

Talk about a “heart-stopper”: as you clear the departure end on the runway outbound, having failed to apply Carb Heat and then… it becomes ominously q u i e t

A’yup, those clever German Engineers, themselves of the Aviation heritage, allowed “as sand-cast” finish of the carburetors to ABSORB waste heat from the cylinders !

Why, by-golly, the transverse cylinder configuration from aeroplanes, made good sense in more ways than one !

As we’ve learned, the Sidestand and Ignition Key “nail” must have been designed in another department or, out-sourced…

 

[melville]

They polish up all pretty:

But yes, that brochure carb looks really rough!