Surging = fuelling issue?

[Steve B]

A call out to the GS1150 Oracles on here.

I have a 2004 1150GS. Bought it at the end of lockdown, and it was absolutely fine for a while.
It then started to surge. I had it in at a local (ex)BMW dealer mechanic (twice). Fully serviced, valves, throttle bodies done, replaced all the tank internals as I fitted an Adv tank (except the fuel pump), even changed the hall sensor. I tried the John Gemi chip, thinking this might be the solution, but no. I removed it at his suggestion to see if it made any difference, but again no. The mechanic thought it was ok after the 2nd visit of tinkering, even after test rides by him and his dad, saying it was smoother than his 1200GSA! The only thing I can think is they must be rough.
I've just returned from a trip to France/Belgium and it was a pig. In top gear it isn't noticeable, or it's not there, but in lower gears and lower speeds, it isn't right. This is my 2nd GS1150 and I loved the last one to bits, BUT I'm starting to fall out with this one.
Could it be the fuel pump that I didn't replace? The bike only has 18k miles on it and I am at a loss as what to do next or where to look.
I think my local mechanic has possibly given up, as he suggested I remove the Lambda Sensor to fool bike into giving it a richer mix. Is surging a symptom of a rich fuel mixture? If I did remove the LS, my only concern here is leaving the hole exposed where the LS is seated in the cat converter. And where would I place the LS anyway?

Any and all suggestions much appreciated before I consider selling it to someone who can figure it out or has the patience.

 

[The Other PaulG]

From memory, there was some discussion about this many years ago. I think that very accurate setting of valve clearances and rocker shaft end float was important in stopping surging.

 

[theoneandonly]

just unplug it . you don't need to remove it. chase the wire up the rhs.
18k on the clock = 1k/year.
what rpm and speed and gear ?
try running 2 FULL tanks of fuel with injector cleaner in it .
that is 2 FULL tanks , not 50 miles and top it off. 400 miles.

 

[Steve B]

just unplug it . you don't need to remove it. chase the wire up the rhs.
18k on the clock = 1k/year.
what rpm and speed and gear ?
try running 2 FULL tanks of fuel with injector cleaner in it .
that is 2 FULL tanks , not 50 miles and top it off. 400 miles.

Apologies for my ignorance, I didn't know you could "unplug" it. I remember years ago I put a Y-piece on my last GS, and I recall having to 'unwind' it and then wind it back in (the only time I've ever used my 22mm spanner!) so it went back in neatly (no twisted wires), but I didn't realise it could be unplugged.
The surging is prominent at lower speeds, 3k rpm, 30mph, 3rd gear and similarly at 20 mph and 40mph.

I guess I should have asked the obvious question, what causes surging? Is it one thing or a combination of more than one? I am hoping it's something quite obvious, and fixable, but the investigation goes on. Not quite there yet.

I'll try the fuel injector cleaner tip (any brand suggestions?). Looks like I'll have to do some long trips with a new Adv tank now on the bike.

Thanks

 

[theoneandonly]

redex , STP , Wynns , anything really , seems to work best with lots of short journeys , so the stuff gets time to work .
OR take them out and have them cleaned £20 /inj ish .

 

[Larry Langford]

I heard that the surging on earlier 4v bmw boxers was a common problem. And by word of mouth, the fix turned out to be more or better input to the computer, ie more sensors, an engineering thing. But I have no idea what can be done in your case. I had a friend who had a bike that did this.
So one of the real guru's will have to make a recommendation, it looks like. I have heard also that you want to have plenty of freeplay in the valves, for another reason.... good luck .....

 

[Nick Marshall]

Just a thought.
Have you checked all 4 spark plugs and caps?

Fuel filter?

 

[Steve B]

Just a thought.
Have you checked all 4 spark plugs and caps?

Fuel filter?

New fuel filter when Adv tank fitted. New plugs (iridium). Caps? I assume the mechanic would have been aware of checking these when he investigated the original problem.

 

[MotoRevive]

Throttle position sensor.

It probably is fuelling.

 

[Steve B]

I heard that the surging on earlier 4v bmw boxers was a common problem. And by word of mouth, the fix turned out to be more or better input to the computer, ie more sensors, an engineering thing. But I have no idea what can be done in your case. I had a friend who had a bike that did this.
So one of the real guru's will have to make a recommendation, it looks like. I have heard also that you want to have plenty of freeplay in the valves, for another reason.... good luck .....

I was under the impression that BMW created the twin spark because of surging on the singlel sparks. I'm just surprised that twin sparks do surge.

 

[JohnnyBoxer]

New fuel filter when Adv tank fitted. New plugs (iridium). Caps? I assume the mechanic would have been aware of checking these when he investigated the original problem.

Does it stutter …between 4-5000 rpm

Or is it lower down the rev range, that the surging occurs

 

[Steve B]

Throttle position sensor.

It probably is fuelling.

Done by the mechanic...twice!

 

[MotoRevive]

Look up "Zero Zero" TPS modification.

I've done it to loads of bikes. It makes them run so smooth. It richens things up. No need to start unplugging lambda sensors.

Are you throttle bodies air tight ??

Surging can also be caused by failing/blocked injectors.

But I think I'd be starting with testing the TPS voltages at all throttle positions. And if it tests okay, do the zero-zero.

 

[MotoRevive]

Done by the mechanic...twice!

Done ? What's he done ? Test it or replace it ?

 

[Steve B]

Does it stutter …between 4-5000 rpm

Or is it lower down the rev range, that the surging occurs

I've kept my eye on what revs and speeds it surges.
3k revs, 30mph, 3rd gear. 4k revs, 40mph, 4th gear. As mentioned in one of my previous posts, it is when I'm 'bimbling' specifically at slow speeds, say, driving slowly through town, which we did a lot of recently on the continent.

 

[Larry Langford]

Well, the way I understand it, it is a fueling problem. They lean out a little, when it shouldn't, which causes the surge in rpm. But somebody surely has come up with a hack for this persistent problem, you would think. Short of ripping off the computer and injectors and installing carbs and analog stuff ..... what say yee ..... This might also be a problem with folks who know a hack but don't want to fix it for free. call up some places, ask around but get an absolute guarantee to fix period .....

 

[JohnnyBoxer]

I've kept my eye on what revs and speeds it surges.
3k revs, 30mph, 3rd gear. 4k revs, 40mph, 4th gear. As mentioned in one of my previous posts, it is when I'm 'bimbling' specifically at slow speeds, say, driving slowly through town, which we did a lot of recently on the continent.

I see
Hard to chase down

 

[Steve B]

Look up "Zero Zero" TPS modification.

I've done it to loads of bikes. It makes them run so smooth. It richens things up. No need to start unplugging lambda sensors.

Are you throttle bodies air tight ??

Surging can also be caused by failing/blocked injectors.

But I think I'd be starting with testing the TPS voltages at all throttle positions. And if it tests okay, do the zero-zero.

He did the TPS more than once, which is why I think he's given up, concentrating on more modern and expensive BMWs.
Can I assume that richer fueling won't have a detrimental effect on the GS? I guess my other question is, is surging a lean fuelling issue?

 

[Steve B]

When I fitted the John Gemi chip, I fitted 1200 injectors too, which didn't do anything obvious. I clearly was following 'the crowd'.

 

[Ian J Hartley]

I recall many years ago on my way back from France I fuelled up with 98 octane from a Supermarket, I usually run the bike on 95 octane as well as set it up at servicing. Anyway the bike was surging like a bastard and was really hard to handle, I was sweating whether I would make the shuttle or not. It wasn’t until I refuelled with 95 back in England that the surging disappeared and the bike settled down.