Sudden slack throttle & rough running.

[macca]

Here's the latest snag with my 05 GS12!
10 miles into a run, on an overtake (!) throttle goes all loose and ultra sensative to any movement and when I pull over, engine sounds rough as hell.
Throttle cable at twistgrip loose, so tightened and all well for 5 mins. Went loose again, so tightened again and got home ok.
Hoping to get to dealer Saturday for them to sort, ( bike under dealer warranty )
Any ideas whats going on? Is it more than just a loose/breaking throttle cable?
macca and out

 

[Pukmeister]

The throttle cable goes into a 'splitter' under the fuel tank, which is a small box with cams that divides the one twist grip cable into two cables that go to operate the left and right 'throttle bodies' (like a carburettor) either side of the engine.

You might find the cable has slipped off the cam wheel inside the 'splitter' resulting in the throttle problems you describe. The reason it now runs badly is because one side of the engine is now asking for more throttle than the other so the engine is running (very) imbalanced.

Thats my best guess based on the symptoms you describe.

 

[macca]

Cheers Adam,
If it goes unbalanced on me again on trip to dealers and I cant sort it roadside, would it be ok to ride on slowly, or would I need to call the men in white coats??!!

 

[Pukmeister]

Macca, I'm only guessing as I haven't seen or heard your bike running. I wouldn't advocate running the engine if my guess is correct. Even over a short journey, there could be a risk of engine damage as one cylinder works much harder than the other. I hope if you ride it to the dealer it is a relatively short journey at low speeds and throttle openings.
It could just be a breaking cable, I can't remember for sure but I think the throttle cable runs the full length from twist grip to one throttle body via the cable splitter box, and the splitter uses a shorter cable that feeds the other throttle body in synch with the first. Someone on here must have had theirs apart or will know the answer for definite.

If either cable were to snap on the way to the dealers, you might have a long walk/wait.

Personally I think if the dealer can collect the bike by van as part of the warranty cover, it would be the safest option. There is also the safety issue to consider, of riding a bike with potentially faulty controls. Not sure how your insurers would take that either if the worst happened and they found out you knowingly rode a bike that was 'unroadworthy' prior to an accident (playing devils advocate here mate).

I hope it is an easy fix, let us know the result.

 

[blobbs]

Look at the left hand cylinder where the throttle cable goes in to it, The cable may have slipped out of the housing. This would cause those symptoms

 

[macca]

OK, heres the best guess at what happenend, because even the bmw tech wasn't sure.
Adam was probably right, and as a result the cable to the left side was loose aswell. I was concerned that I saw bare throttle cable at the twistgrip end, which I tightened, and which held till I got to dealer.
The collective wisdom of the BMW service staff and interested onlookers was:
the cable may have been pinched when tank last replaced, and as bike only done a couple of hundred miles since, has slowly worked loose, dropped back into position on cams and this accounts for sudden loose cable. Originally the servicing mechanic may have missed the pinch, saw the tight cable and loosened it at the bar end adjuster.
The dealer tech guy, checked it through for me, talked me through the correct position of the cables and reasured me that he was satisfied all ok, with correct adjustment. Much obliged to all for your thoughts.
( the original service which caused the error was not BMW motorrad - before I purchased bike.)
macca and out

 

[Pukmeister]

Had a similar problem on my bike about a year ago, managed to prise open the splitter box lid catches and reseat the LH cable.

I rechecked the manual (poor memory, getting old!!) and it is one throttle cable to the splitter box, then two cables to the throttle bodies (eg 3 cables in total).

Glad you got it sorted.