What controls idle balance on a 1200GS?

[GrinningGSer]

First service just done and bike running better after reporting surging. but made a manometer for checking things and warm idle balance is out by about 6 inches !
Slackened throttle cables and balance still out.

Obviously, the throttle cables could be used for balancing, but should not be used for idle balancing ?

There are no air screws or any other visible means of adjusting idle balance or tickover on a 1200GS.

Does anyone know how this is done ?

 

[Raindancer]

Throttle (idle )adjustment

Try this link. It may help

http://www.ukgser.com/forums/showthread.php?s=&threadid=41499


Dan

 

[GrinningGSer]

Try this link. It may help



I have waded through the forums but have not found the answer....
Yes, valve clearances critical
Throttle cable balance critical for smooth acceleration and speed running...
But nothing re 1200GS and IDLE balance

As far as I can see, there is no means of idle adjustment on the 1200, unlike other boxers. Surely idle is not balanced mechanically by the throttle cables ? Maybe it is somehow electronic?

Answer not found yet in any forum links that I have seen

 

[Raindancer]

CARB SYNC MANOMETER

HI again.

I was about to say look under the "Technical" forum fourth item down under the above heading.

But just checked it again and noticed that you are already on there with your question.


Duhhh sorry I should have read it more closely.





Regards

 

[Marty Hill]

The stepper motors balance the idle. No adjustments necessary or possible.

 

[Mouse]

As far as I know, Marty is correct in that the balance at idle is controlled by the stepper motors in the throttle bodies. I'm sure adjustment is possible, but only via the BMW disgnostic computer. Job for the dealer

 

[Wraithwrider]

On speaking with the technician at Jefferies no adjustment is in fact possible.

If idle isn't sorted by the stepper motors then there's a problem that needs sorting.

They evidentally can stick.

 

[GrinningGSer]

Well guys, I have all of the symptoms that you have discussed on the thread :http://www.ukgser.com/forums/showthread.php?s=&threadid=31377&highlight=stepper+motor

I have a new Feb05 1200GS and suffer surging at about 2500rpm on deceleration which makes slow speed work and cruising difficult and spoils what otherwise is a fantastic bike. It is my first boxer and I thought at first that it was just a learning process and different engine characteristics to my last 4cyl, but now 1000 mls and still there.
Things are better since my 1st service last week and I asked for throttle balancing check

But- being the sort of nosey person that I am, I read reams of threads, built a manometer and shock horror, balance is out at tickover and thereafter onwards up the rev range
This a little disappointing immediately after a service

I have never heard of 'stepper motors' but must assume that it is back to BMW for electrical balancing ?

Can anyone explain what a stepper motor is ?

Mouse, it would seem that you have balanced idle by means of throttle cables, but I feel that someone will offer a good technical reason why this is not the thing to do ?

Wraithwrider- has your surging been corrected ? I cannot believe that a Feb05 bike would need software remapping, but what do you think ?

I am gathering knowledge so that I know what to ask from BMW

 

[Wraithwrider]

The surging on decelleration is an old problem that you shouldn't notice on a Feb 05 bike. The cure was a software update way back in 2004.

My 1200 was supplied in Oct 04 and I've had no surging at all. So I would take it up with the dealers because your bike seems to have a fairly isolated problem.

Throttle body balence at idle and on an open throttle is adjusted by two different means.

When the throttle is open it is adjusted by the use of a manometer and the cable adjusters inboard of the throttle bodies themselves. You normally adjust just the one side to match the manometer readings - easy. Make sure the outer cable ends are properly seated in the adjusters though!

At idle it's a different story. I was initially under the impression that the BMW tech adjusted the balence using the computer plugged into the bike during service. On talking to Jefferies' top man he says that isn't actually the case. The stepper motors do the job automatically and there's nothing that you, I or they can do to adjust it!

Stepper motors as I understand the technology are motors that move in discreet steps as opposed to smoothly. So presumably the motor (fitted each side on the top of the body going down inside) is connected to a sensor which senses something, maybe flow, and then incrementally adjusts the balence when appropriate.

Now anything that adjusts in steps isn't going to provide the same sort of balence as a simple analogue manual adjuster as used on older bikes. This may be the problem I suspect.

My bikes idle was super smooth from new. After the 600 mile service I noticed that it can be quite lumpy. A manometer confirmed that the balence was 2 to 3 cm out.

I had the bike checked by Jefferies and they assured me that it was in spec. They suggested that I get some miles on it (now 2750) and if the problem persists they will take a look at the stepper motors which can stick/fail.

The stepper motors shouldn't be a factor in your surging though.

Sorry about the long post but sometimes short snappy answers don't really address the question.

 

[GrinningGSer]

Very interesting. I will need to pass this on to BMW. The surging is minimal, but noticeable and I wondered if it was the imbalanced idle, when the throttles are shut, which is causing this.

Regards.

 

[Mouse]

Mouse, it would seem that you have balanced idle by means of throttle cables, but I feel that someone will offer a good technical reason why this is not the thing to do ?

Actually I balanced my throttles at about 4000 rpm, which (obviously) didn't affect the idle at all, but did make it smoother when using the lower rev range.

 

[birdseye]

Mouse - did it make the bike any smoother at 4000 rev and above?

I'm suffering from numb hands brought on by engine vibes at motorway cruising speeds, to the point where motorways are impossible. Have been wondering about making a manometer but am not sure that it isnt an issue of basic engine balance. Why when the engine has a balancer shaft, I do not know. But currently its more vibey that a new Harley Softail!

 

[Mouse]

Yes, it did. People have said that on the older bikes, the throttles need to be balanced as often as every 3000 miles.

I think your vibes would be cured by balancing. Do a search for threads on how to make a manometer from plastic tubing

 

[R45]

R45

Hi Guys!
I'm new here, live in Taiwan and ride a 1200GS.

just for your info, you cannot do any of the balancing yourself
unless you have the "GT1" computor.
The idle is controlled by "stepper" motors and is not adjustable,
for balance under load (the throttle cables) you need to turn off
these stepper motors, which is only possible through a GT1.

If you try to balance under load without having switched of the
steppers, you will get an incorrect reading on the vacum guages
as the stepper motors will constantly try to compensate and
consequently balance will quite possibly be even worse!
For you guys that used to fiddle around yourselves (like
me), this era has passed (GT1 Euro 15'000.- +)

 

[Wraithwrider]

R45

Do you mind if I'm contrary and suggest that the stepper motors only operate at idle.

From where does your info come?

Peter

 

[Mouse]

You could always unplug the stepper motors, but I haven't found this necessary. I doubt they have enough movement to create much difference at large throttle openings.

 

[Wraithwrider]

The way that I look at it is this:

If the throttles are opened by the trottle cables then they effectively 'hang' on the cables above idle, just as per previous BMW twins.

Therefore the relative adjustment of the cables regulates the balance of the throttle bodies at all positions above idle.

I believe that the stepper motors have nothing to do with anything but the idle set up.

They are about discreet and fine incremental adjustment in resonse to signals obtained by measuring differences in pilot air flow across the two throttle bodies at idle. I'm quite amenable to being proved wrong on this but it doesn't make engineering sense to have them somehow regulating balance above idle too. They would have to sort of 'follow the throttles' as they were opened to do this. This isn't what stepper motors do.

Evidentally early 1200's did have idle adjustment screws fitted together with the stepper motors. Therein I believe lies tales of adjusting idle balance by disconnecting the stepper motors. The problem I see with this anyway is that as soon as you re-connect them they negate the manual adjustment anyway! I don't believe that disconnecting them above idle would serve any function at all.

I wish the manual explained how things work. I assume that there must be Technical data out there. This stuff isn't rocket science.

Peter

 

[Wraithwrider]

How can you tell I'm busy?

I've just been through the manual and extracted this:

Quote

Note that synchronisation does not affect cylinder balance and engine rpm at idle speed. In order to ensure that they do not affect syntonisation with the throttle valves slightly open, the idle actuators must be brought to a defined position with the aid of the BMW Motorrad diagnostic system.

Test
Check that when the throttle grip is released, both throttle valves are fully closed irrespective of the position of the handlebars.

Both throttle valves reach the idle stops.

Slight play is perceptible at the throttle cables of the throttle valves. (1 to 2mm)


Test
Use the BMW Motorrad diagnostic system to set the engine management system's idle actuators to synchronisation mode. To do so, follow the instructions issued by the BMW Motorrad diagnostic system.

Using BMW Synchro (No. 130831) , (No. 130832) , (No. 130833) , (No. 130802) measure the difference of the average values (AVG) of the partial vacuum in the air intakes with the throttle valves slightly open.

Unquote

So what does all this mean? Well for Motorrad diagnostic system read GT1. For idle actuators read stepper motors.

Effectively R45 was spot on - apologies for doubting you!

With the throttle valves SLIGHTLY open the stepper motors can (I believe that can is the right word to use here) effect sychronisation.

The problem being that whatever revs you use to set up the balance, because the engine is not loaded, the throttle valves will only be 'slightly open' so the stepper motors COULD effect your readings.

There's no mention of adjusting idle synch in the manual presumably because it's done automatically by the aforesaid stepper motors.

Max Dp for the throttle bodies is given as 15 mbar.

So now we know.

Peter

 

[Wraithwrider]

And I can now think of why idle synch can get worse after a service:

Stepper motors are put to the 'park' position for the sych procedure.

When they're re-energised they automatically synch to at setting which is within spec but not as good as before the service.

It all makes sense now.

 

[birdseye]

And I can now think of why idle synch can get worse after a service:

Stepper motors are put to the 'park' position for the sych procedure.

When they're re-energised they automatically synch to at setting which is within spec but not as good as before the service.

It all makes sense now.

It doesnt really make sense, any more than the servo brakes do. BMW engineers have done it this way "because they can". The stepper motors seem like overcomplication for the sake of it, just like the servo and the canbus, and thosebl**y self cancelling indicators. And of course it means you have to use your dealer for servicing.