Oilhead throttle bodies tend to wear out (the right is more common). There are a lot of different throttle bodies available for these bikes so if you are sourcing a used one, you need to make sure you get the correct one. Each TB has a stamping on the bottom casting rib.
On the original Oilheads, there were two basic designs. For the GS and the R, the throttle body closes at a 5° angle, and for the RS and the RT it closes at a 10° angle. The 10° angle gives a different throttle tip-in response. The brass air screw on the GS throttle body is also larger. Starting with the R1100S and continuing through the R1150 models, the same design is used for all bikes and it appears to have a 5° plate angle. The injector mounting is different; using one of these requires a different fuel distributor and injector. The bore on all models is 45mm.
Given below are the stampings I can find and the BMW part numbers.
|Bike||Left TB||Right TB|
|R1100RS and RT to 7/96 1||45/101
13 54 1 340 613
13 54 1 340 614
|R1100RS and RT 7/96 to 9/98 2||45/105?
13 54 1 342 245
13 54 1 342 246
|R1100RS and RT 9/98 on 3||45/111 ?
13 54 2 325 851
13 54 2 325 852
|R1100GS and R to 7/96 1
13 54 1 341 685
13 54 1 341 686
|R1100GS and R 7/96 to 9/98 2||45/107
13 54 1 342 269
13 54 1 342 270
|R1100GS and R 9/98 on 3||45/113
13 54 2 325 853
13 54 2 325 854
|R1100S and all R1150 models 4||45/109
13 54 1 342 495
13 54 1 342 496
13 54 7 669 725
13 54 7 669 726
1 The earliest Oilhead have a one-piece throttle cable which loops around the pulley on the left TB and then crosses over to the right TB. There is a separate attachment for the choke cable on the left TB. The right TB cable angle is nearly perpendicular to the TB, but the left one is raked back about 30° .
2 These Oilheads have a throttle cable splitter box that controls each TB separately. The left TB has no choke cable attachment, because the throttle is advanced in the splitter box and there's no attachment for the crossover cable housing. The cable mounting angle on the right TB was changed to match the left TB. These may be NLA and superseded by the next.
3 In 9/98 they changed the design so that the pulleys were pressed onto the shaft, rather than held on with a nut and washer. This change was retroactive to replacements (my replacement 45/102 had a pressed-on pulley). Cable and cable mounting angles seem to be the same as before.
4 The 1150 throttle bodies have a differently-sized hole for the fuel injector.
Contrary to popular belief, replacement TB parts ARE available from Bing USA. Complete rebuild kits are currently $165 each and include the shaft, seals, end caps and other small bits. The relatively useless German Bing website is http://www.bingpower.de/.
Repair is an increasingly attractive alternative as prices rise. Currently a pair of throttle bodies retails for about $800. The left TB is over $500 because a new TPS is included.
When the throttle body gets loose, it may be the shaft that is worn.
You may be able to substitute the shaft from a different throttle body. The left TB on all models has a longer shaft because it has to turn the TPS.