Throttle stop screws............?????

[Gavin4333]

When I checked my throttle balance at 12,000 miles (the 1st service I carried out) the balance was spot on at idle and 3-4000 revs so I never looked in detail at the throttle stop screws.
However just carried out 18,000 mile service and found that at idle and revs the balance was out of sync by the same amount, ie when revved the out of balanced did not alter - odd as the throttle stop screws should dictate idle balance and the cables dictate balance at revs.
The reason for this was that the throttle stop screws were not touching the plates (by a couple of mm's!!) and the throttles were 'hanging' on the cables, with obviously no slack.
So what I've done is:
Slacken off both cables (5mm as per manual)- engine hardly ran.
Using a thin piece of paper as a gauge screwed both screws in so they were just touching the plates. The orignal sealing appeared to be intact.
Balanced at tickover to achieve 1100 revs by adjusting each screw slowly.
Set cable freeplay to about 5mm and balanced at 3-4000 revs.
Checked the balance several times and everything stayed spot on.
Left it overnight to cool and tried it in the morning - spot on again.
Rode 50 miles and rechecked - still spot on.
So the question is: Have I done this right, because searching the forums has thrown up many statements saying NEVER touch the throttle stop screws, but not any reason - and my logic says that what I did is correct and that the reason to have them is to balance the tickover.

Any comments welcome, especially as I leave on Friday for a couple of weeks in the Dolomites and the Alps!!!!!

Thanks

 

[Steve]

So the question is: Have I done this right,

Yes. (that was easy wasn't it?)

 

[Kenny Rodkiss]

odd as the throttle stop screws should dictate idle balance

I think it is the large brass 'air bypass screws' that dictate idle ballance and not the throttle stop screws which are not used unless you are trying to do a complete throttle body set up.
If you had a gap betwwen the screw and plate then you shoud have slackened the cables to give a small amount of slack.
B*W recomend zero slack but that can lead to noisy butterflies.
If the tickover was then too slow screwing out the air bypass srews will increase tickover speed.
Then you have to balance them so left and right are giving the same readings.

 

[Gavin4333]

Kenny, I tried that before I touched the screws - the brass air screws were, and are again, set at 1 turn out, without any success.
Also my BMW manual says 5mm slack (with a detail drawing - if really needed!!).

Forgot to say that it is running as good, if not better than before, with very stable tickover and no surging (it has never suffered from this).

As you say Steve it seems right so I think I might be being overly concerned - but let me know if you think different, I'm always willing to admit to being an idiot (comes from lots of practice!!!!!!!!!!!).

 

[Steve]

Ahhh, sorry. I misread the post. It is, as Kenny says, the large brass screws that should control both the idle speed and the idle balance.

 

[(RIP) Kaister]

having just done my throttle body balance, idle speed , zero=zero, and 4k on the centre stand balance - i've got a few questions.

what are the brass 'idle' screws' actually controlling ?

the reason i ask is that after doing everything, i reckon my idle is slightly rich.

usually, you do a balance at idle , check at 4000, adjust cables within the slack range to balance so that idle is un affected and then adjust idle mixture screws for highest idle speed to give correct idle mixture, then reset the stop screws.

I had to use the idle mixture screws to get the right idle speed - as you're saying also - and i'm not sure about it.
I think i should go back and re-adjust for highest idle speed on the brass screws, then reset the stop screws for correct speed and ballance - seeing as they aren't connected.

this is all hypothetical at the moment though - as i'm currently 'without'

 

[Kenny Rodkiss]

screws

The large brass screws are air bleed screws and they bleed air into the inlet tract.
Unscrew anti-clockwise (out) to let more air through and this has the effect of speeding up the tickover on that throttle body, which will give you a lumpy tick over untill you adjust the other side to match.
You should be using the screws to balance the bodies at tickover and then use the same screws to adjust tickover speed to your preference.
They are not used for highest idle speed.

These screws will not affect your tickover mixture as this is taken care of by ECU.
If you think your mixture is rich then do all the obvious checks not forgetting the Lambda probe.
Do a search for more indepth info.

 

[(RIP) Kaister]

ok - so why does unscrewing' automatically' speed up idle speed ?

surely - for correct idle speed the mixture is at 14.67:1 already ? - ie stoichometric.

more air = slower idle

as does

more fuel .

correct air / fuel = highest speed, most complete combustion ??

I don't understand this theory then. ?

done searches - read everything - etc

please explain this more and completely kenny

 

[carbold]

Unscrewing the idle screws will let more air into the cylinders. This excess of air is detected by the lambda probe and the ECU will send more fuel to the injectors to keep the ratio air/fuel close to the stoichometric one. The net effect is more fuel (air+petrol) in the cylinders i.e. higher idle speed.

 

[(RIP) maverick]

Gavin what you did was pretty logical and correct although it is not advisable to fiddle with the stop screws as it controls you TPS setting as well. So if you set the LHS throttle stop screw you might of set the TPS voltage out of range or by the sounds your moto is running actually into range. But if you merely screwed them back untill they just touch the stop plate it should not give any problems.

I fiddled with mine for weeks untill someone found a dodgy TPS problem. Replaced and have not looked back since

 

[Gavin4333]

Thanks for your thoughts, as I'm fairly happy with the running I'm going to leave it as it is but I think I need to find out a bit more about this type of fuel injection - then I can really fiddle!!!!!!