Working on this R1100RS I've found it has a worn throttle body. It's only 20 years old, not 30 as is the KBike. I'm yet to extract it from the bike but it will either be the bushes mounting the butterfly arm or the arm itself, which is often the case as I've read.

This was easy to diagnose as it ticks when it's running and the gauges showed it jumping.

Now if this 20 year old has worn bushings on it's bing throttle bodies, why wouldn't a 30year old kbike have the same issue. It's just easier to hear the problem on a twin

Hmmm interesting maybe has something to do with heavier pulsing of air due to the big twin. Sort of rattling the butterflys around or that they are on their lonesome with one on each side and not in a brace as the bricks are.

Yeah, I know they say 'Don't touch the Throttle Bodies' but they must wear after 30 years. This seems to be a common R1100 problem and they are 10 years newer and look exactly like a kbike behind the engine . They also have the set screws loctited. You can buy kits from bing USA to fix the R1100, dunno about the K100. I guess the TB on a 1100 twin is about twice the size and double the forces than a KBike. Something to consider though. I reballanced my K100 bodies using the carbtune and it's never run better

It uses more fuel though

Hi robin. Just to clarify, given the subject of the thread.
Did you sync the brass air screws on the K TB's or, shock, horror, the linkages?
Just wondered.

If by RS1100 you actually mean R1100RS, yeah they do that.  I had an R1100R with rattly throttle bodies, mostly on one side due to the way the cables are setup.  Many carburettor specialist can do something for you.

Al

The TB linkages. It's never run so well. I spent several hours looking for air leaks before the carbtune arrived and found none. I could not balance it using the bypass screws so got the loctite off the screws and adjusted the linkages. I got inspiration here -> https://www.k100-forum.com/t1526-how-to-balance-the-throttle-bodies-solved?highlight=TB+balance  TB 3 is the master, the rest slave of it.

Now I'm messing around with this R1100RS, the set screws on it are also loctited. But it's TPS is different, it relays the throttles actual position to the injection system so a number of people are doing a zero=zero adjustment on their set screws so the TPS is actually set to off when the TB's are really off. There is a problem with surging when cruising around 4K on these bikes and all this is part of the reason why. I also pulled a TB off that bike today and the shaft going through the tube which holds the butterfly was wiggling up and down. The shaft/bushings are worn in that TB and need parts. I got bits coming from Romainia of all places to fix it.

It seems the right goes first, then the left. To my way of thinking, if these Bing TB's can wear why not the ones in the KBikes?

My 1100R never surged at all but the 0=0 throttle synch did make it much more responsive.

Al

A mate of mine has a 97 GS and he had surging. The BM dealer told him to run it in a lower gear to get around the issue  

People don't seem to be afraid to remove the TB loctite from these bikes 


Al, how do you get the plugs out?  What sort of spanner fits? This $2K special has no tool kit.

Mine had it's toolkit, with plug socket included.  That bike is long gone now though.

Al

I can remember riding one of the first K100's back in '83 and it was very smooth. I know time can blur the memory but I remember it as much smoother than the CB750 I had at the time.
You do have to wonder if wear has occurred in the butterfly spindles and/or the linkages after 40 or 50 thousand miles. It might be a BMW but they ain't perfect!
It was always common practice to adjust Jap engines at the carb linkages. 
Maybe it made more sense for BMW to sync the throttle bodies on a flow gauge as part of an efficient production line and bolt them on ready to go rather than some exotic set up.
We know that syncing them using the air bleed screws can make a difference to tickover and surely if the butterflys are a bit out it will affect the running higher up in the range.
The attitude does seem to be if its got loctite on it you can't touch it or it may explode. A few of us have disconnected or disabled the TPS and feel that its a nicer bike to drive. No exposions yet!
There has been a recent thread about ways of reducing vibration via filling handlebars with lead, sand, etc. I suffer from mild Carpel Tunnel Syndrome in my wrists and the vibes at around 60-65 mph can be an issue for me.
Think I might check the shims, stick in a new air filter and give it a go. After reading those couple of write ups on how to do it, I'll clean up the air screws, close them and see what kind of readings I get on the Carbtune just on the TB's at several points on the rev range.
If they're out, I'll have a go at adjusting them.
Absolute worst case scenario, I'll have to buy another set of TB's on eBay.

John, I did this one as it wouldn't balance using the brass screws. If it will balance by adjusting the brass screws, I'd suggest it's not broke so don't fix it

Using TB number 3 as a reference, my number 2 was good but number 1 was down some and number 4 was way down. It's possible there are air leaks that I couldn't find causing those two to be low, I didn't pull it all apart for a closer look.

After the balance I noticed the knocking from the output shaft area when cold had been reduced significantly. Previously I had to hold the choke to position 2 to stop the knocking when cold, now choke position 1 is enough to stop the knocking till it warms up. And when it does knock, it's no where near as loud as it was before the balance. Also idling is a lot smoother and power delivery throughout the rev range is a lot better. 

It definitely worked for me

RobinW wrote:A mate of mine has a 97 GS and he had surging. The BM dealer told him to run it in a lower gear to get around the issue  

People don't seem to be afraid to remove the TB loctite from these bikes 


Al, how do you get the plugs out?  What sort of spanner fits? This $2K special has no tool kit.

 BMW do a plug spanner, both the original too-kit one and a decent "workshop quality" item. After messing about with the cheap and nasty tool-kit one I bit the bullet and paid seventeen quid for the better one. It was worth it as it fits down the tunnel easily and it has internal spring clips that hold the plug so that it threads cleanly first time.



"Surging" is more a symptom of poor valve adjustment than anything else. It's fiddly making certain that the pairs of valves are as near as possible exactly the same. To do this you need two feeler gauges and work both at the same time (having three hands would make it even easier). I use Wurth ones and after spending so often on the floor picking up one that has slipped out, I added a cord so that they'd only drop a short distance. 



With the valves adjusted and a decent TB balance, surging often disappears.

Worn TBs are a constant problem with 4-v Boxers.

Cheers Mike. I'm dropping the rear drive off at the shop tomorrow for new bearings then heading out of town for the week. I'll try and get a spanner off him when I pick it up. None of the spanners I have here fit. Chris Harris has a tappet adjustment video on utube for the boxer. It's great to see it being done by someone that knows.