BMW doesn't show a part number for the o-rings that go around the air screws on each throttle body. I checked the Bing website (http://bingcarburetor.com) and they only list throttle bodies for the R-series bikes.  However, when I called he was able to look up the part number and verified he had some in stock. They are about $2.25 USD.

I didn't think to ask him the part number, but I can report back with the part number once I receive the package. I'm working on an 1985 K100RT with throttle body assembly 95/34/401. Maybe I'll record measurements of the new ones so at least the measurements are available after the Bing o-rings are unavailable.

Goodonya, Mikey. We look forward to either the dimensions or a valid Bing part number.

I recall someone on the forum not too long ago posted that they'd found a satisfactory substitute somewhere...I'll have a squiz and make a link. Having both yours and their info in one location is great for future repairs.

MaxBMW shows an o-ring p/n 13 11 1 257 819 that is used in conjunction with the adjusting screw P/N 13 54 1 461 261.  These o-rings seem to only be used on the 2 valve engines.

Since the adjusting screw is the same between 2V and 4V then it could be safe to assume the o-rings would be the same. I note the o-ring is an Airhead carbie piece as well - it's the enrichment lever (choke) shaft o-ring on Bing 32 & 40mm carbies.

TWB, true, but the MaxBMW fiche doesn't list the o-ring for the 16v k100rs. 

???

I guess someone will need to pull a screw on a 4v and see what's there.

Oh sure enough, it was hiding without a number in the diagram. Thanks for pointing that out. I didn't look closely enough. I naively looked up and down the parts list for "o-ring". I wonder if "...only in conjunction with Gasket ring" means they can only be purchased together and not separately, though they are priced separately.



Well, it's good to know they can be replaced. My o-rings were flattened and glazed. Plus I have the throttle bodies out so it's a good time to change them.  The needle ends of the screws were carbon coated also, so cleaning up them and their air passages may be an improvement at idle.

Hi there,

Do any of you know the dimensions of the o-ring? Inner diameter and thickness is needed. My electronic caliper is out of order at the moment .

Edit: I took one o-ring out of the air screw and drove to autoparts dealer to find a suitable one. They had 5.0 x 1.0 O-rings, which I installed. So far so good. Original seems to be very close to 5.5 x 1.0 or 1.25. Case closed for the time being.