One cylinder misbehaving

I recently went off roading in rather deep mud on my 2007 (May) BMW R1200GS, during my ride a branch/twig caught on something near the throttle cable, under the handlebars. Following this, the bike seemed to run on 1 cylinder then die.

Then trying to get it to run, the throttle had no impact on the revs of the bike, it stayed at idle. So I used my fingers to twist the butterfly flap and do the throttle manually via the left-hand cylinder. That's when I noticed that the plastic throttle guide had snapped. I did this manual effort to get me out of the mud, I was panicking slightly but I do remember it running only one cylinder...

Since coming home, I've taken the bike apart in efforts to ascertain why the bike no longer runs on two cylinders. I've fixed the plastic throttle guide - But still nothing. It has good compression, 155 psi both sides however when I take my vaccuum guages to the throttle bodies, the cylinder which is not firing has no vacuum. Based on this, I thought to check the valves or piston rings. I've done the valve clearances, although to be fair they weren't really out and I've ensured that there is no valve damage, the piston rings are also good.

I bought a GS-911 scanner and there is no fault codes, annoyingly! I've also synced the throttle bodies via the GS-911 scanner.

I'm really stuck, any advice would be SO helpful!!

Will it idle ?

Do both header pipes get hot ? (Be careful not to burn yourself).

Your bike should idle even if you have no throttle cables. Have you checked for a spark ?

There's lots I don't understand... Which plastic throttle cable guide? How can it not pull a vacuum - it would do this with no electrics attached, it's physics... - unless there's a big hole somewhere permanently open to the cylinder head.... If you operated the butterflies yourself, then presumably that's singular, since you could only operate one and (somehow) ride out of the mud? That would mean only one cylinder getting the juice.... No?

I'd be looking for something mechanical first. If it was that sudden a change and you're aware it was throttle cable related. What about the Bowden box! It's well protected, but maybe the cables got screwed up and only one is now operating? But you've flummoxed me with that no vacuum thing. How can they be??

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Ditto , can’t imagine why lack of vacuum, bottom spark plug hasn’t come out has it?

Failing that I’d be checking for sparks

It sounds like one of the throttle cables has got hung up at the junction box. The outer cable has come out of its locating hole at the splitter box. One of the reasons it won’t idle.

So your throttle cable has sustained an impact. Enough to break the guide.

Have you actually checked to see if the throttle cable operates both throttle bodies in unison.

I would be looking at the throttle cable linkage through your Bowden control box, as Slipperyeel has suggested, as this seems the most likely problem area.

Steptoe is on the button......listen and learn.

Popell said:

Ditto , can’t imagine why lack of vacuum, bottom spark plug hasn’t come out has it?

Failing that I’d be checking for sparks

Click to expand...

re-read the symptoms and mixed up vacuum with compression, so my suggestions is utter bollocks!


Sorry about that