To recap, My left side TB made a racket.
Listen here. (The "tack, tack" you hear is from the throttle plate pivot shaft banging around inside it's pivot in the TB.) Does yours? With the engine running put your finger on the pulley for the throttle cable. Its on the inside of the TB between the TB and the engine. If the noise stops your throttle shaft is worn out.
My search yielded these alternatives for a fix:
- Buy a replacement from BMW - $300.
- BingCarburetor.com has a rebuild kit for $75. It's not listed on their website - call and ask for TS. Tell him you want the rebuild kit. You need the Bing part number which is stamped into the web on the bottom of the throttle body. My part number was: "BING 75/45/109"
- Beemerboneyard had a left side TB with position sensor available for $130.
I was in a hurry so I went the quick and easy Boneyard route. If I'd had the time, I would have gotten the rebuild kit from Bing and learned something new.
I replaced the TB, did the "zero=zero" setup and balanced the TBs. The clackety noise is significantly reduced but not quite gone. I wonder if the salvage TB is slightly worn? I recorded the noise of the salvage TB for comparison sake.
Listen here..
Also, my bike has had a persistent roughness or "stumble" at very small, steady throttle openings between 3K and 4K RPMs since I picked it up - 50K miles ago. I initially thought it was the fabled BMW twin "surging" and became very familiar with IBMWR.org, my TwinMax and a box fan - balancing the TBs in repeated, unsuccessful attempts to eliminate it.
About 20K miles ago, when I installed a shorter torque arm and Ohlins, I did experience "surging", a "rum, rum. rum" in fourth gear in the 3-4k rev range, which I also was never able to TB balance away. It progressively went away on it's own. I think it might have been due to a realignment of the drive shaft u joints caused by the longer shocks and a shorter torque arm. I was never able to really tell for sure. And it's gone now.
Anyway, the really good news is that the stumble is now significantly improved with the better, salvage TB. It's still there but much less noticeable. I can't help wonder if I'd rebuilt the TB instead of installing the salvage one if the throttle roughness would have been eliminated altogether.