Off idle "stumble"?

[Taipan]

Hi All
My 94 R1100GS has a nasty "stumble" when first opening the throttle. Its in the first 1/8th of its travel at low revs. It seems to stumble a bit and is very jerky if trying to hold a constant slow speed, say 1st gear filtering through traffic. It seems to idle slightly unevenly too?
This is my first Boxer and I know nothing about them. Does this sound like a common fault such as balancing?
Thanks for any thoughts, advice, ideas etc.
Best,
Dave

 

[MrIFan]

Had a similar but not identical problem with my 95 1100 when I first got it. Traced it to the fuel tank water drain (the little hole just under the filler cap) being blocked and water getting in to the fuel every time it rained!!! HTH

 

[YoYo]

Aaah the famous "surge". Do a search on here, or even better, on the Advrider site. Make sure that you have a day or two available...

By all means, do check the drain hole, but when I had that issue, it was on all revs, and quite a bit stronger than the surge you seem to describe. You'll find it easier to clean if you remove the filler lid.

Oh, and make a serch on "Techlusion" as well...

 

[turbine_2]

Could be throttles slightly out of sync or something a bit more serious. I have a simalar problem at the moment which was initially diagnosed as throttle bodies being out of balance, then went on to being a dead lambda sensor, a dead motoronic control unit and is now being diagnosed as either a dying ignition coil (which is where my money lies at the moment) or a faulty injector.

 

[YoYo]

To clarify my reply: "They all do that, Sir..." Especially the 1100, due to the "L" shaped gas wire train. The "Y" shape of the 1150 helps a bit, if I'm correctly informed.

Adjusting the valves and syncronizing the throttle bodies does help a bit. What really helped for me was to bump the TPS voltage up to 0.385 V from 0.350. Don't go over 0.400 V, as this is said to affect the Motronic.

Of course it still surges... Only less!

 

[Taipan]

Oh joy of joys an inherent fault!

I rode an 1150 yesterday, it was a lot smoother and would pull cleanly from idle when filtering in traffic. It also had a lot more initial grunt. So maybe mine does need the throttles balancing?

I have a morgan carbtune for a twin cycliner engine. I wonder of that would work ok on the BMW? Anyone used one on their bikes?

I'll go and search for balancing, but any tips or dos and dont will be gratefully recieved

 

[Steptoe]

I'll double check the balancing while it's here

( some of those above suggestions not for your model )

 

[(RIP) Kaister]

idle balance

then mixture - reason is that at idle the lambda is controlling the mixture - then as you open it up it merges into the ECU map.

how that transition takes place - and the step - is the off-idle hesitation - its either going rich or weak - my guess is rich

take it to a dealer - or better still DIY - get them to specifically check idle balance, CO2 mixture,valve clearances and mid range balance

or steptoe

 

[MikeO]

Aaah the famous "surge". Do a search on here, or even better, on the Advrider site. Make sure that you have a day or two available...

Doesn't sound anything like surging to me...

Mike

 

[Rob Farmer]

Sounds like the throttles just need balancing to me, you also need to check the throttle screws. Your bike doesn't have a Lamba sensor so there's no point worrying about that.

If that doesn't cure the problem check the throtle body/cylinder head rubbers. One split on my 95 1100 and that upset the low speed running till it was replaced.

 

[Taipan]

Apparently it was slightly out of balance? Steptoe soon sorted it though. It runs much much better now and is a lot smoother when riding. I can even see out of the mirrors now!! Top bloke that Steptoe. Cheers Neil