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Hugh003
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100 Mile House, BC
Joined: 05/27/2012
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Do I have the air tube clamps correct? Should the double clamps be on the carb? The bike is a 1976 R75/6.
Thanks.

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schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
Posts: 6586
My 1978 /7 is like yours,

My 1978 /7 is like yours, with two clamps at the air filter housing. This is the arrangement on RealOEM:

https://www.realoem.com/bmw/enUS/showparts?id=0333-USA-09-1977-2474-BMW-...

Note that I have item #2, so one clamp squeezes it around the housing stub and one clamp squeezes around the plastic tube. Note that the RealOEM page says up to 9/78. I've not been around a lot of different models, but I heard people do it many ways. Actually, I don't see where two clamps at the inlet to the carb makes much sense...where's the second clamp going to go?

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Hugh003
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100 Mile House, BC
Joined: 05/27/2012
Posts: 35
The RealOem site for 1976

The RealOem site for 1976 shows the two clamps at the carb:

https://www.realoem.com/bmw/enUS/showparts?id=0292-USA-05-1976-2476-BMW-...

MikeL46
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VBMWMO #9300
Joined: 01/01/2016
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Two clamps on top

Every Airhead I've worked on had two clamps at the air box and one at the carb - except the R90S which has to be the other way around.

Mike

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67 R50/2 w/R100 engine/trans and Ural Sidecar
69 R60/2 76 R90S 78 R100RS
70 Triumph w/Spirit Eagle Sidecar

Randolph
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2 clamps on bottom

On my 1976 R90/6 the two clamps are at the carbs as Hugh mentions. The difference is an aluminum spacer (item #3) in the tube at the carb end. I took mine apart and removed the spacer to show you. I guess the spacer is to keep from crushing the tube with the clamp.
There are also 2 slots cut diametrically opposed at the top in my tubes. This allows the tube to collapse a bit on the o-ring on the air box stub. If you use the rubber grommet on top the o-ring probably doesn't matter.
Either way, 2 clamps up or down, I've always thought the tubes are a hokey way to bring air to the carbs. The tubes don't quite fit squarely at either end so I wonder about leaks. So either way you do it is adequate I guess, just hokey.
-Randy

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  • alu_spacer_in_tube.jpg
  • alu_spacer_removed.jpg
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schrader7032
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VBMWMO #7032
San Antonio, TX
Joined: 10/27/2006
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Interesting...I've never seen

Interesting...I've never seen the insert spacer used on these air tubes. Neither of the RealOEM links above shows it. The R90/6 link does show it but it's grayed out indicating that it isn't used for that model.

It does show up on the R90S image:

https://www.realoem.com/bmw/enUS/showparts?id=0278-USA-08-1974-2476-BMW-...

Maybe that's because the R90S uses Dell'Orto carbs whereas the rest of the lineup uses Bings. And for the Dells, there are two clamps at the bottom. Suggests to me that the Dells are different animals in terms of their attachments.

Note that the tubes are different sizes left and right since the cylinders are staggered. And they really have one orientation that is correct. While technically they can be installed either end going into the carb, one of the orientations will result in an awkward slant of the tube leading into the carb throat. I never really knew that until one day I was visiting the St. Louis BMW show in their downtown location. The service manager took a look at the bike and side my tubes were installed upside down. He quickly fixed them for me!

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Kurt in S.A.
'78 R100/7 '69 R69S '52 R25/2

Randolph
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R90S tubes

Thanks for the info. So it looks like I've got some R90S tubes. I notice the P/N for the R90S grommet is different also. The input port OD for the Dell is probably different. The Bing is 50mm OD and the ALU ring is 1.5mm thick so it might be a reducer ring to match the Dell.
I removed the ring and tried the tube on the Bing but it's a sloppy fit. Even with the clamp the tube will slide rotationally on the carb. Are there slots cut in the bottom of the tubes you've seen like the slots in the top of mine? The slots may help the tube tighten up when the clamp is applied.
Ah, learning more every day. I think I'll leave my setup as is since the o-ring seals nicely at the top.
I believe blaming the POs for anything unusual is SOP for these bikes, right?
-Randy

RickR90s
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Farmington Hills, MI
Joined: 11/28/2016
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Clamps

MikeL46 wrote:

Every Airhead I've worked on had two clamps at the air box and one at the carb - except the R90S which has to be the other way around.

Mike

Exactly Mike,

Because of the Dellorto's on the R90s, there are two rubber grommets. So there's room for 2 clamps at the carb and 1 clamp at the air box.

Most Bing's I've seen only have the grommet at the air box, hence two clamps there and one at the carb.

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RickR90s

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