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Rich
09-22-2007, 10:16 PM
Hiya Jim,

Not one to do a whole lot of my own maintenance, I was motivated while going through all your "how to" threads, which you have do a super job on!

Today I tackled the valve adjustment and throttle body adjustment on my 07 GS. My bike has been idling rough, and backfiring more than I thought it should. The valve job went smoothly, and everything was pretty good except I had a tight exhaust valve on the right side. Easily taken care of with your directions, and I got them all adjusted in less than a hour. Not bad for a rookie.

Ok, on to the throttle body adjustment. I guess I was one of the unlucky ones. My idle on the Twinmax bounced, with a 2 as the center. You say you have never seen that, but I sure did. Lucky me..... :banghead

Anyways, I ran the RPM's up, at 2K and 4K the needle was dead center, or too close to worry about. So then I started to look at the idle you say there is no adjustment for. I crawled below and watched the bodies move (with the bike off) as my wife ran the throttle, and I could see a stopper screw where the spring loaded plates stop against.

So looking at the top of the bodies, I saw a rubber cap covering a 10mm screw. By backing out the left throttle body screw, I was able to bring my Twinmax needle to center, which started out way to the right. I gotta believe that is probably the way to adjust the idle, you can take a look and verify if it looks right to you. My idle immediately smoothened out.

Here's a picture of the screw, it has some blue silicone looking goober on it that held the rubber cap on, or maybe it is blue locktite. In either event, it was easy to adjust.

http://rp.smugmug.com/photos/198934614-L.jpg


I just took the bike out and it runs smoother than ever. And it quit shaking at idle, which is why I was wanting to do this work in the first place.

I'm pumped! Thanks for all the good info you provide, it's easy to follow and understand.

I'm off for an afternoon ride!

Rich

cboulden
09-24-2007, 01:39 AM
Rich i have a 05 12rt and on my first tune up i performed myself at 18000 i looked at a tb sync for an 04 1150 and i assumed that this screw with the blue thread locker on it was the same brass screw used on earlier models to adjust idle speed, well after 3 weeks and 850 dollars and 2 new throtle bodies later, i learned the hard way not to touch these screws, i to obtained a better and smother idle but the following morning the bike was difficult to start, and would not hold an idle for 15-30 seconds, once warmed up it ran ok but stumbled on throttle opening, the dealer thought he could take the tbs off another new bike and measure the clearence of the opening, this proved impossible for the dealer, in the end bmwna service rep advised that these are set at the factory on a bench flow meter and matched at the factory, since that time i purchased jims video and no longer worry about the idle, please be carfull adjusting these screws, as a point of shame i was told by the bmw rep that i was the first person to screw up there tbs by adjusting this screw.

deilenberger
09-24-2007, 02:06 AM
Rich,

That is the screw that is IMHO never to be touched. Idle sync is done by the stepper motors that Jim shows unplugged. Apparently the dealer can tweak this sync with the GT1 computer.. the blue screw is the base setting for the throttle plates - and is set at the factory by putting the throttle bodies on a flow bench to match the closed positions.

Rich
09-24-2007, 02:51 AM
You guys have me concerned now. Good thing I kept an eye on how far I turned it, if that matters.

In my tiny mind I would think that you would adjust the plates for a syncronized idle with the stepper motors disconnected, but it appears I'm incorrect by your statements.

I did a cold start this morning and went for a nice ride. It fired right up and idled great. The bike is still running smoother than ever, and even when I started it cold it didn't shake like it has been before I did any tweaking. The Givi windscreen that normally fluttered wildly now sits almost perfectly still.

So the big question: Do I put the screw back to where it was? My plan is to leave it as is, as long as it runs good. (I just ran out to the garage and started the bike again, it idles like a dream.)

What do you guys think? And thanks for your comments.

jimvonbaden
09-25-2007, 04:03 PM
HI Rich,

I would make a note of how much you moved the screw, then ride it as is for a while and see if you have any rideability issues with it. Since you know the original setting, you should be able to get it back close enough that the stepper motors can ajust for it.

I suspect you wont, though I agree with Don. The stepper motors will keep the bike close to tune, even if the Twinmax isn't showing it. However, I am very curious if the screw you adjusted moved the butterfly valve? If it did, that would be a bad thing, because the stepper motors will have to try to compensate.

I'll check into this when I get a chance, and see if I can determine for sure what the function of the screw is?

Thanks for the input,

Jim :brow

PS I just don't get what happened with Carl's bike. I can't see how he irreperably damaged the TB's, nor why a competant tech could not reset them?


You guys have me concerned now. Good thing I kept an eye on how far I turned it, if that matters.

In my tiny mind I would think that you would adjust the plates for a syncronized idle with the stepper motors disconnected, but it appears I'm incorrect by your statements.

I did a cold start this morning and went for a nice ride. It fired right up and idled great. The bike is still running smoother than ever, and even when I started it cold it didn't shake like it has been before I did any tweaking. The Givi windscreen that normally fluttered wildly now sits almost perfectly still.

So the big question: Do I put the screw back to where it was? My plan is to leave it as is, as long as it runs good. (I just ran out to the garage and started the bike again, it idles like a dream.)

What do you guys think? And thanks for your comments.

Rich
09-26-2007, 03:04 AM
It sounds like Carl went to cranking on both sides, which probably got everything out of wack. He can add details if he reads this. Hard to believe it would require new bodies, you would think someone could put them back to specs.

It appears to me that the screws are the close stops for the plates. You can see a little ear on the plates that actually close and rest against the screws. I actually backed off the left side screw about 90 degrees, letting the plate close a hair more. That's my take on it. My adjustment didn't affect the reading at higher RPM's at all.

I will take your advice and ride it, I have a 4 day ride planned in the Black Hills this weekend. I should know by then if something is amiss.

jimvonbaden
09-26-2007, 03:36 AM
I agree, and it sounds like a reasonable plan!

Keep us informed as to what happens!

Jim :brow


It sounds like Carl went to cranking on both sides, which probably got everything out of wack. He can add details if he reads this. Hard to believe it would require new bodies, you would think someone could put them back to specs.

It appears to me that the screws are the close stops for the plates. You can see a little ear on the plates that actually close and rest against the screws. I actually backed off the left side screw about 90 degrees, letting the plate close a hair more. That's my take on it. My adjustment didn't affect the reading at higher RPM's at all.

I will take your advice and ride it, I have a 4 day ride planned in the Black Hills this weekend. I should know by then if something is amiss.

Rich
10-05-2007, 01:17 AM
Several cold starts, a short warm-up idle, and a 1000 miles later, all is well. :thumb

jimvonbaden
10-05-2007, 01:08 PM
Several cold starts, a short warm-up idle, and a 1000 miles later, all is well. :thumb

Sweet!

Something I noticed on Tina's bike when I did the 24K last week is that hers has no covers on them like the GS. Probably because they are under a fairing piece.

My friend Kermit is going to do his 36K this weekend, and has complained about his idle being rough. I told him about this, and he will likely give it a try, keeping very close tabs on exactly how much he moves the screw.

Thanks for the update!

Jim :brow

burnszilla
10-07-2007, 12:26 AM
With the stepper motors disconnected what should the idle RPMs be?
I'm using a Synchromate2 and it also tells you the RPMs.

burnszilla
10-07-2007, 02:22 AM
I reckon 1100 RPM +/-50

jimvonbaden
10-07-2007, 08:05 PM
With the stepper motors disconnected what should the idle RPMs be?
I'm using a Synchromate2 and it also tells you the RPMs.

The stepper motors don't effect the idle rpm. It should be around 1100 +- 50.

Jim :brow

maxscycle
10-09-2007, 10:02 AM
The stepper motors don't effect the idle rpm. It should be around 1100 +- 50



Forgive please, just what do the stepper motors do? Or control?
max

jimvonbaden
10-09-2007, 11:34 AM
The stepper motors don't effect the idle rpm. It should be around 1100 +- 50



Forgive please, just what do the stepper motors do? Or control?
max

Unless a dealer tells us, and none seem willing to do so, we are only guessing, but since several tests at idle with the stepper motors connected, then disconnected, have shown absolutely no changes, most of us are guessing it controls off idle transitions, and possibly idle balance, but not idle speed apparently.

Jim :brow

deilenberger
10-09-2007, 12:13 PM
Unless a dealer tells us, and none seem willing to do so, we are only guessing, but since several tests at idle with the stepper motors connected, then disconnected, have shown absolutely no changes, most of us are guessing it controls off idle transitions, and possibly idle balance, but not idle speed apparently.

Jim :browThis is a case where I would have beg to disagree.

The stepper functions should be identical to the function of the BBS (Big-Brass-Screw) on oilheads and the fast-idle control.

The BBS set the idle throttle body balance AND the idle speed. The butterflys are set to a default position at the factory and are not to be field adjusted. The steppers control idle speed - especially duing cold start, just like the fast idle lever did on the oilheads.. they allow more air around the butterfly to maintain idle speed on a cold engine.

It's unclear to me what "off idle transitions" are..

For a test of the stepper functions.. stop the engine after idling when hot. Disconnect the steppers - then let it cool overnight and try starting it. Bet it won't idle happily when cold.

Disconnecting and reconnecting at a single temp (a warm engine for instance) won't show a difference between connected and disconnected - since the system doesn't have to compensate for temperature of the engine.

jimvonbaden
10-09-2007, 12:28 PM
Points well taken Don, and they make sense.

I will test the theories out on the next TB sync.

Just a case in point though, I did disconnect the Stepper Motors with the engine cold, and warmed it up on one bike, TB off slightly. Plugged it in and it was still off. But only once, so hardly definitive, and the bike didn't idle well until it was warmed up. It is also possible that the stepper motors only function is to act like a choke, electronicly. So far either the dealers don't know, or they are not saying.

As for not adjusting the butterfly set screws, I would normally agree on an oilhead, but maybe not necessarily on the Hexhead, this remains to be seen as well, as there is some evidence that this is a viable way of setting the balance at idle.

NOTE: I am NOT recommending anyone move the butterfly screw, just not convinced it is going to cause the same issues it caused on the Oilheads!

Good discussion, and we are all learning as we go.

Jim :brow


This is a case where I would have beg to disagree.

The stepper functions should be identical to the function of the BBS (Big-Brass-Screw) on oilheads and the fast-idle control.

The BBS set the idle throttle body balance AND the idle speed. The butterflys are set to a default position at the factory and are not to be field adjusted. The steppers control idle speed - especially duing cold start, just like the fast idle lever did on the oilheads.. they allow more air around the butterfly to maintain idle speed on a cold engine.

It's unclear to me what "off idle transitions" are..

For a test of the stepper functions.. stop the engine after idling when hot. Disconnect the steppers - then let it cool overnight and try starting it. Bet it won't idle happily when cold.

Disconnecting and reconnecting at a single temp (a warm engine for instance) won't show a difference between connected and disconnected - since the system doesn't have to compensate for temperature of the engine.

Rich
10-09-2007, 11:54 PM
I'll keep watching this thread for further updates as it moves along.

As far as the what appears to be an unsyncronized idle, has anybody had this problem and actually had it smoothened out by the dealer adjusting the stepper motors the way Don described?

I'm just curious if it is a normal everyday problem?

I'm with Jim and Don both, don't go cranking on the screws just yet. I may have gotten lucky, and I'd sure hate for someone to really mess up something that maybe just shouldn't be messed with.

AntonLargiader
10-10-2007, 12:28 AM
The stepper motors do function like the BBS' did. Idle speed AND balance.

Idle speed: try this: while your bike is running, unplug an injector. What happens? What happens on an R11xx?

Balance: self-ex and I think it's pretty clear.

Bottom line: there are no user adjustments for either one so it's pretty logical that the computer deals with it. It does this by reading the crank speed on each firing stroke and adjusts each side (fuel and air) as needed to maintain the right RPM and the right balance between the left firing strokes and the right ones. It knows which is firing by reading the cam sensor on the right-side cam, and it monitors the engine speed by the HES which reads the teeth on the front balance shaft drive gear.

As for the sealed throttle stops, IMO just like the R11xx you can make an adjustment that works with the ECU's assumptions or you can make one that makes it harder for the ECU to adjust. Sounds like Rich did the former and Carl did the latter.

All that the user can do is adjust the cable synch (really, this is all the dealer does also but he does it without the steppers interfering). I don't know if the steppers will try to smooth out the part-throttle operation or not.

jimvonbaden
10-10-2007, 01:18 PM
The stepper motors do function like the BBS' did. Idle speed AND balance.

Idle speed: try this: while your bike is running, unplug an injector. What happens? What happens on an R11xx?

Anton, I'm not sure what you mean by this? On the R1100/1150, the idle goes to crap, and it runs on one cylinder. Obviously that will also happen on the R1200, but what does that have to do with the stepper motors?

Balance: self-ex and I think it's pretty clear.

Bottom line: there are no user adjustments for either one so it's pretty logical that the computer deals with it. It does this by reading the crank speed on each firing stroke and adjusts each side (fuel and air) as needed to maintain the right RPM and the right balance between the left firing strokes and the right ones. It knows which is firing by reading the cam sensor on the right-side cam, and it monitors the engine speed by the HES which reads the teeth on the front balance shaft drive gear.

As for the sealed throttle stops, IMO just like the R11xx you can make an adjustment that works with the ECU's assumptions or you can make one that makes it harder for the ECU to adjust. Sounds like Rich did the former and Carl did the latter.

All that the user can do is adjust the cable synch (really, this is all the dealer does also but he does it without the steppers interfering). I don't know if the steppers will try to smooth out the part-throttle operation or not.


So, essentially, you are saying I have been doing it right all along?

Thanks Anton, I know you have occasional access to the GT1, so I figure you have an insite. From what you just said, the GT1 does NOT adjust anything at idle, the bikes computer does it all by itself via the stepper motors and the spark timing? Or was it just the stepper motors?

Thanks again,

Jim :brow

mneblett
06-23-2009, 08:41 PM
Dredging up an old thread -- please bear with me, as I didn't see another subsequent thread on the same subject.

I'm curious whether in the 1 1/2 years since the last post in this thread, anyone has gained any more experience with adjusting the "thou-shall-not-adjust-me" throttle stop screws.

I expect my new '09 RT will smooth out a bit as it breaks in, but as of today (~1100 mi.) it is idling a bit rougher than I would expect (yes, I know -- "it's a boxer, it's gonna rock and roll at idle" :)) My expectation though, based on the 4 boxers currently in the garage, is that the counter-balanced R12 should idle smoother than my wife's R1150GS.

So, when/if I ever get any free time, I intend to throw the TwinMax on the bike to get a current baseline reading at idle for future reference. Then, at some point in the future, if no one has had any further problems with tweaking the stop screws, the curious ex-engineer in me will probably start fiddling with the screws to see whether an adjustment helps smooth things out, or whether, even if adjusted, the steppers cancel out the throttle stop adjustments anyway when they are reconnected.

Also, before I do so, I will seek out a better understanding of the stepper motors' specific function -- as I currently understand it, the stepper motors control the air bypass around the throttle plate for *both* idle speed and cold start high idle control. I suspect they also are coordinated with the fuel injection amount in response to the closed-loop O2 sensors for emissions purposes (once the O2 sensors are up to operating temp).

FWIW, at the moment at least, I'm guessing that the the reason the stop screw adjustment is "critical" is that the stepper motors have only a limited command authority, and therefore the throttle bodies have to be set up in a relatively narrow range of adjustment to ensure the stepper motors can exercise bypass control over the entire intended operating range. Accordingly, if they are adjusted enough that one or both of them are out of the "acceptable" range and the stepper motor can no longer provide enough bypass flow to meet the engines requirements, the engine runs poorly.

If that is correct, I'm guessing that the stop screw adjustments are not so much "critical," but simply intolerant of large movements away from the factory settings -- settings made on a flow bench to a tolerance of "good enough" for correct operation with the stepper motors, but not necessarily "perfectly" matched to obtain the smoothest idle. In other words, I suspect that a bit of fine tuning to improve balance should be well tolerated as long as the throttle plates remain within the operating range of the stepper motors.

Well, that should stir up things a bit :D Seriously, I'd appreciate further thoughts/debates/suggestions from the Collective. Thanks!

Mark

azgman
06-23-2009, 09:59 PM
Mark, I read somewhere (I'll have to search a bit to see if I can find the reference) that it is possible to adjust the stepper such that it binds up and cannot be fixed. I thought that the source of info was reputable at the time. The story was that they had to buy a new TB to solve the issue.

marchyman
06-23-2009, 11:41 PM
Some comments about idle sync from an amateur....

The RepROM states that an idle imbalance of up to 25 mbar is allowed. I assume that is with the steppers parked. Until the GS-911 adds that function I'll just have to trust that things are close enough without parking the steppers. Anyway, the manual states that if the imbalance exceeds 25 mbar at idle you should

1) check for air leaks
2) check the valves

This makes lots of sense to me. I'd be very wary of playing with the stop screws when making sure that the valves match side-to-side might be all that is needed. I've watched folks do valve adjustments and while all are very careful to make sure that the valves on each side match, some are not so careful about matching side-to-side. That is, one side may be slightly tighter than perfect while the other side is slightly looser than perfect.

If my idle goes to hell I'm going to take extra care on the valve settings.

New2rt
06-25-2009, 02:28 AM
I can give you some information on the stepper motor from the automotive application, how much it translates to BMW MC's, I don't know.

The stepper motor controls idle by bleeding air past the throttle plate, it is also responsible for the air bleed (idle increase) during cold start.

When we would set the base idle, it was done using a scanner and monitoring the stepper motor reading. Engine at normal operating temp. The base idle was adjusted until a specific stepper reading was reached.
(base idle was set by changing throttle plate position using a stop screw or an additional air bleed screw)
I needed the scanner because as the throttle plate was opened the stepper would close and vise versa, rpm's would stay the same. not reading the stepper motor position could cause it's operating limit to be exceeded.

The stepper motor had a given operating range, if it was exceeded it would damage the motor in short order.

I would think BMW could recalibrate the throttle bodies without replacing, they have to do it anyway. Turn around time might be another issue. I would guess that a good service tech can also come close by reading the stepper motor on your bike but the key word is guess.

I for one would not touch these screws unless I could read the stepper position and return it to that setting. Even then it's the idle and I'm not usually at that position too long.

Hope this helps.

To add to this I'm not a fan of unplugging them to check idle balance. There are two and to unplug them and get them in sync would be a challenge. They constantly change and would cause balancing to two different stepper settings, unless you can lock them equally, I would leave them plugged in.

deilenberger
06-25-2009, 03:40 AM
To add to this I'm not a fan of unplugging them to check idle balance. There are two and to unplug them and get them in sync would be a challenge. They constantly change and would cause balancing to two different stepper settings, unless you can lock them equally, I would leave them plugged in.Stepper motors inherently "self-lock" when de-energized. They resist moving from the "step" they're in. And on the R12 series - the two move in sync. They don't move independently of each other.

The latest GS-911 beta software has the ability of "locking" the steppers for balance adjustments, and has had the ability for some time, of reading the stepper motor positions. That's how we found out the two move in sync.. so to me - it really doesn't matter if the TB balance is done with them connected or disconnected - since they're in sync, and only really effective at or very close to idle (which isn't where we're balancing the TBs) - they have no effect on the end result.

One thing I believe is coming on the GS-911 will be the ability to change the base settings of the steppers so as to be able to adjust the idle speed. Not that I've ever had my bike stall on me - but having the ability might be nice.

deilenberger
06-25-2009, 03:49 AM
Mark, the perfectionist in me likes what you're thinking of doing.. the hesitant to touch screws that are never to be touched engineer wouldn't suggest doing it.

I'd love a perfect idle on my R12R - but since I don't ride at idle, I found I am capable of ignoring less than perfection - especially since it's a bit temperature dependent. I agree with your analysis - and the caution Marchyman makes - make sure everything else is perfect before making adjustments to the TBs.

So far on my bike - if I get the valve adjustment what I consider anally perfect - sync above idle is as perfect as I can measure on my TwinMax at maximum sensitivity. Maybe I'm lucky - but I'm guessing BMW did get it right when they initially set it up. Given that perfection where I actually ride the bike - I've decided to just ignore the slight rocking at idle - and think of it as character.

BTW - you might take a look at the DIY/Tech area - there are some great writeups there with very clear illustrations of what is being adjusted and why..

Best,

New2rt
06-25-2009, 11:15 AM
Stepper motors inherently "self-lock" when de-energized. They resist moving from the "step" they're in. And on the R12 series - the two move in sync. They don't move independently of each other.

The latest GS-911 beta software has the ability of "locking" the steppers for balance adjustments, and has had the ability for some time, of reading the stepper motor positions. That's how we found out the two move in sync.. so to me - it really doesn't matter if the TB balance is done with them connected or disconnected - since they're in sync, and only really effective at or very close to idle (which isn't where we're balancing the TBs) - they have no effect on the end result.

One thing I believe is coming on the GS-911 will be the ability to change the base settings of the steppers so as to be able to adjust the idle speed. Not that I've ever had my bike stall on me - but having the ability might be nice.

I ordered the GS911 but it is currently backordered, from what I read it has the ability to zero the steppers and until I get it I'm not sure what this means (lock for throttle sync or sync to each other) I figured they moved together but did not know if they were at the exact same setting as compared to each other.
(same as a throttle sync, they move together but one will be at a different setting as compared to the other) Hope you understand what I'm trying to say cuz I sure don't

deilenberger
06-25-2009, 02:57 PM
I ordered the GS911 but it is currently backordered, from what I read it has the ability to zero the steppers and until I get it I'm not sure what this means (lock for throttle sync or sync to each other) I figured they moved together but did not know if they were at the exact same setting as compared to each other.
(same as a throttle sync, they move together but one will be at a different setting as compared to the other) Hope you understand what I'm trying to say cuz I sure don'tThe steppers show the same number of steps at all times - ie - they move in sync. No independent control apparently (which is actually understandable since we don't ride at idle..) And yes - even the current GS-911 software has the ability to zero the steppers (I've done it - idle drops, then the ECU takes over again and brings it back up if the engine is running..) but since they move in sync, I see no reason or need to use it for balancing the TBs.

Wallowa
06-25-2009, 06:05 PM
Another issue related to balancing induction via throttle body cable adjustments with, in my case, a TwinMax...throttle body cable end or free play...specs call for .5-1mm at TBs and .5mm at grip [R12s]...how do you folks adjust this and how do you get them equal, right/left, and within specs?

Also we balance via only one TB cable, in Jim's video and in Haynes manual the right side, that seems counter intuitive to me to only increase or decrease one side to match the other...plus doesn't that then change the free play balance?

Thanks for any ideas or comments...

mneblett
06-25-2009, 06:25 PM
Another issue related to balancing induction via throttle body cable adjustments with, in my case, a TwinMax...throttle body cable end or free play...specs call for .5-1mm at TBs and .5mm at grip [R12s]...how do you folks adjust this and how do you get them equal, right/left, and within specs?

Also we balance via only one TB cable, in Jim's video and in Haynes manual the right side, that seems counter intuitive to me to only increase or decrease one side to match the other...plus doesn't that then change the free play balance?

Thanks for any ideas or comments...
I've never thought of it in terms of any sort of "balance" of cable slack -- the slack specs are there to ensure that the throttle plates will definitely go to their rest positions when the throttle grip is released, no matter what effect temperature/handlebar turn angle/etc. may be having on the cables. There is no need for the slack to be "matched" -- only that there be at least a sufficient minimum slack at all the cable ends.

In fact, you can't balance vacuum if you are constrained to keep the slack exactly the same. Balancing is done because the cables are two microscopically different lengths -- balancing effectively shortens or lengthens one cable so that when the throttle grip is operated, both cables pull their throttle valves open at the time. Maintaining equal slack precludes "matching" of the cable lengths.

I tune for vacuum balance, and then double check afterwards that there is enough slack at all the cable ends. If not, I mutter under my breath :) and then adjust the cables generally equally on both sides to increase the slack, and re-sync the vacuum balance (and then again double check for the existence of slack).

That said, I rarely have to adjust slack -- the balancing adjustments are so small that they rarely ever eat up enough slack to require adjustment.

As to which side, it used to be that BMW called for adjustments on the right side. With the newer, different throttle cable arrangements, it doesn't matter which side you adjust, as long as sufficient slack is available -- and there should be no need to adjust both sides (again, unless there's insufficeint slack on one side), because you are only changing the relative flow between the sides (i.e., adjusting up on one side would have the same effect as adjusting down on the other).

HTH!

Wallowa
06-25-2009, 07:29 PM
I've never thought of it in terms of any sort of "balance" of cable slack -- the slack specs are there to ensure that the throttle plates will definitely go to their rest positions when the throttle grip is released, no matter what effect temperature/handlebar turn angle/etc. may be having on the cables. There is no need for the slack to be "matched" -- only that there be at least a sufficient minimum slack at all the cable ends.

In fact, you can't balance vacuum if you are constrained to keep the slack exactly the same. Balancing is done because the cables are two microscopically different lengths -- balancing effectively shortens or lengthens one cable so that when the throttle grip is operated, both cables pull their throttle valves open at the time. Maintaining equal slack precludes "matching" of the cable lengths.

I tune for vacuum balance, and then double check afterwards that there is enough slack at all the cable ends. If not, I mutter under my breath :) and then adjust the cables generally equally on both sides to increase the slack, and re-sync the vacuum balance (and then again double check for the existence of slack).

That said, I rarely have to adjust slack -- the balancing adjustments are so small that they rarely ever eat up enough slack to require adjustment.As to which side, it used to be that BMW called for adjustments on the right side. With the newer, different throttle cable arrangements, it doesn't matter which side you adjust, as long as sufficient slack is available -- and there should be no need to adjust both sides (again, unless there's insufficeint slack on one side), because you are only changing the relative flow between the sides (i.e., adjusting up on one side would have the same effect as adjusting down on the other).

HTH!

Thanks...lots of info here...when I mentioned 'balance' in my post it referred to induction balance...AKA 'synchronisation' of right to left TBs...evidently that balancing out of TBs can be affected by the amount of free play/slack/end play...let me quote the Haynes manual:

"Note: It is essential that freeplay is the same in both cables, otherwise the operation of the throttle valves will not be synchronised"

Your description of fiddling with the slack and synch painted a good image...and one I can relate to...my original question was how do we measure that ".5-1mm" freeplay? I guess we just eyeball it. What I hear is that freeplay is not critical [if within specs?], but that it should be the same on both cables...or at least within specs...which at .5-1mm means they are damn near identical...as I understand the freeplay is between the cable housing the metal adjuster at the TB...the cable does not have freeplay...If cable housing is too loose or too tight it can affect the operation of the cable inside that housing.

OK...back to the shop and another shot at it!

Thanks again..

mneblett
06-25-2009, 08:12 PM
let me quote the Haynes manual:

"Note: It is essential that freeplay is the same in both cables, otherwise the operation of the throttle valves will not be synchronised"

The number of mis-statements and errors in the Haynes and Clymer manuals would fill a book ... um, come to think of it, they do. :)

It is not "essential" that the freeplay be the same on both sides -- only that some freeplay exists. The 0.5-1 mm spec is really there to make sure people don't leave just an RCH of slack, and then later have a throttle butterfly hung open. At the other end of the slack spec, you actually could put as much slack in as you want (but you wouldn't, as you'd be annoyed with how far you have to crank the throttle grip before the cables start moving the butterflies).


...my original question was how do we measure that ".5-1mm" freeplay? I guess we just eyeball it.
Sorry if I wan't clear. Yes -- if you can lift up on the cable ferrule and see at least a half mm of slack, it's fine.


but that it should be the same on both cables...or at least within specs...which at .5-1mm means they are damn near identical...

Nope :) -- see above comments regarding Haynes :D


as I understand the freeplay is between the cable housing the metal adjuster at the TB...

the cable does not have freeplay...If cable housing is too loose or too tight it can affect the operation of the cable inside that housing.
Yep!

marchyman
06-25-2009, 09:09 PM
The latest GS-911 beta software has the ability of "locking" the steppers for balance adjustments, and has had the ability for some time, of reading the stepper motor positions.

Beta? Oh, I see there is a new one. Thanks for that info. The previous release would let you sync the steppers side-to-side, but not lock them. Time to do some downloading. Good timing, too... my 48K service is around the corner.

New2rt
06-25-2009, 11:11 PM
The steppers show the same number of steps at all times - ie - they move in sync. No independent control apparently (which is actually understandable since we don't ride at idle..) And yes - even the current GS-911 software has the ability to zero the steppers (I've done it - idle drops, then the ECU takes over again and brings it back up if the engine is running..) but since they move in sync, I see no reason or need to use it for balancing the TBs.

Huh, I did not know that, I was thinking they can self adjust to allow an equal power pulse at idle from each cylinder. Now I see why that special screw begs to be turned. My bike is new and I'm sure breaking the seal would not be good for warranty and actually I kind of like the character idle.

Thanks for the information