Airscrew Adjustment to fix off-idle stumble and Throttle Body Sync - w/ pigtails

[kjetil4455]

Hello, thank you for this post. I hope I can get some help here with my problem as I have tried to calibrate my throttle bodies as well.

I recently bought a 2012 ST. It runs pretty well but is extremely weak in idling, and I choke it (ie it turns off) if I don't turn the throttle very carefully when I am initiating forward motion. I don't have so much experience with big heavy bikes, so the lack of an effective clutch really makes me make a lot of mistakes and I already dropped the bike once due to this.

We have increased the CO2 in both cylinders to "10". We also set the throttle body bleeding screws to 3/4, but this made it run horrible. I live in south america and this type of MC isn't common here, and the mechanics don't know so much about them. I personally am certainly no engine expert, but I am overall techy and hope I can sort this out, so I started reading online and realized I needed a proper manometer. So we tried again: We turned the WHITE (bypass) screw to 3/4 and checked the vaccuum pressures, and they were way off. C1 had 6cm Hg higher pressures than the second cylinder. Unfortunately, however, and this is what I was hoping to get some advice on; turning the second (non-dominant) screw does nothing at all. Being completely closed or open, it does not change the vac pressure in the second cylinder. So in the end, what we had to do to get a half-assed calibration was to open the WHITE screw by 2.5 full turns from closed position, and leave the NON-DOMINANT screw completely closed. This way we got almost to spec at approx. 1.5 cm Hg difference in pressure (using a liquid mercury manometer).

For the vaccuum pressure I've seen done by others, it is around 24cm Hg. We ended up at like 18cm Hg at fair calibration. I presume this, indeed, is a problem.

Is the throttle body damaged, is that why turning the non-dominant screw does not work? Or is there some maintenance that can be done to fix this? I'd like to reach 0 difference. Finally, is it a problem that the white screw is 2.5 full turns? The throttle response does seem much positively improved after what we did.

Sorry for a long text, this is my first post.

 

[Wallkeeper]

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Wally

 

[eemsreno]

Hello, thank you for this post. I hope I can get some help here with my problem as I have tried to calibrate my throttle bodies as well.

I recently bought a 2012 ST. It runs pretty well but is extremely weak in idling, and I choke it (ie it turns off) if I don't turn the throttle very carefully when I am initiating forward motion. I don't have so much experience with big heavy bikes, so the lack of an effective clutch really makes me make a lot of mistakes and I already dropped the bike once due to this.

We have increased the CO2 in both cylinders to "10". We also set the throttle body bleeding screws to 3/4, but this made it run horrible. I live in south america and this type of MC isn't common here, and the mechanics don't know so much about them. I personally am certainly no engine expert, but I am overall techy and hope I can sort this out, so I started reading online and realized I needed a proper manometer. So we tried again: We turned the WHITE (bypass) screw to 3/4 and checked the vaccuum pressures, and they were way off. C1 had 6cm Hg higher pressures than the second cylinder. Unfortunately, however, and this is what I was hoping to get some advice on; turning the second (non-dominant) screw does nothing at all. Being completely closed or open, it does not change the vac pressure in the second cylinder. So in the end, what we had to do to get a half-assed calibration was to open the WHITE screw by 2.5 full turns from closed position, and leave the NON-DOMINANT screw completely closed. This way we got almost to spec at approx. 1.5 cm Hg difference in pressure (using a liquid mercury manometer).

For the vaccuum pressure I've seen done by others, it is around 24cm Hg. We ended up at like 18cm Hg at fair calibration. I presume this, indeed, is a problem.

Is the throttle body damaged, is that why turning the non-dominant screw does not work? Or is there some maintenance that can be done to fix this? I'd like to reach 0 difference. Finally, is it a problem that the white screw is 2.5 full turns? The throttle response does seem much positively improved after what we did.

Sorry for a long text, this is my first post.

Just for kicks, try setting the co2 up to +50 or 60. I've had great results with this.

 

[Bill_C]

Per the manual, if that bypass air screw (the non-white one) doesn't do anything you need to remove and clean the throttle body. Just be careful and follow the manual. If you don't have one, then one of us can post pictures of the pages you need.

Sent from my SM-S906U using Tapatalk

 

[kjetil4455]

Per the manual, if that bypass air screw (the non-white one) doesn't do anything you need to remove and clean the throttle body. Just be careful and follow the manual. If you don't have one, then one of us can post pictures of the pages you need.

Sent from my SM-S906U using Tapatalk

Thanks Bill, yeah I saw that, so we are planning a cleaning on wednesday. Not sure exactly how this is done to restore normal calibrative potential for the left screw, but I hope the mechanic does. As I said in the post, they are not well versed in these bikes and I am a newb, so I am trying my best to come prepared.

Just for kicks, try setting the co2 up to +50 or 60. I've had great results with this.

Thanks man. We raised it to 10 today. It was 0 on cyl2 and 5 on cyl1. Will see if we can fix the throttle body sync and pressure, and if we do, I'll keep trying around with the CO2 levels. I saw other people on this forum recommending "6", but I have seen higher as well. Will try your advice!

 

[kjetil4455]

UPDATE for the misfiring between 2-3000 RPM on my super tenere. I also noticed that it was misfiring more when it rained and, also, more during higher altitudes. Reduced the CO2 to -10 and it got better, but clearly did not go away. We finally changed the 4 coils, however, and the problem completely resolved. I guess the last cleaning we did on the coils and the coil cylinder's walls just made it short circuit more and that's why this - coincidentally - started after also changing the CO2 settings. Runs like a kitten now. We also redid the TB calibration after replacing the coils, and changed the two tiny o-rings that help sealing the bleeding screws because they were flattened, and it was once again difficult to regulate the vacuum pressure using the bleeders.

 

[TenereGUY]

Reading this thread... I was getting ready to do a TBS... but I need to adjust the CO 1st. I have a 2017 and 14+ models have to have that done at a dealer. Then I can get it home and do the TBS or would the TBS be included in the CO setting? Is the CO setting a one time thing and then I can check my TBS once a year at home?
TIA,
Guy

Sent from my SM-N960U using Tapatalk

 

[kjetil4455]

Careful with the CO settings, they change the ECU fueling quite significantly. High CO settings made my stock bike run like shit. I live at 1000m altitude, and a CO between 0-5 worked best for me. You can experiement with it a little. I recommend leaving them stock unless you live at very high altitude or in very cold climate (both of which would require running leaner or richer)

Set CO somewhere between +10 (cold climate) or -10 (high altitude) depending on your needs (I don't know why, but after changing the CO you'll have to ride for a while before you really feel the changes and become aware of which setting is better). and then do the TB sync

I leave my CO at what's appropriate for my home town and I don't change it if I go to the mountains. I would change it if I LIVED in the mountains. It's a one time thing presuming you're living at the same place. I don't know if it's worthwhile to raise CO at winter time, but it's possible to try.

 

[eemsreno]

Reading this thread... I was getting ready to do a TBS... but I need to adjust the CO 1st. I have a 2017 and 14+ models have to have that done at a dealer. Then I can get it home and do the TBS or would the TBS be included in the CO setting? Is the CO setting a one time thing and then I can check my TBS once a year at home?
TIA,
Guy

Sent from my SM-N960U using Tapatalk

You are correct that the dealer must change the CO settings on 14 and newer. You would have to ask them to do the TBS if you want them to do that, it is totally separate. Just for reference it takes about 30 minutes of labor to change the CO setting if the dealer knows what he is doing.
My 17 is set to +45 but if I had easy access to it I would try +55. My 2012 is set at +60 right now but it is easy to change.

If you have a flashed ECU this might not apply.

 

[TenereGUY]

You are correct that the dealer must change the CO settings on 14 and newer. You would have to ask them to do the TBS if you want them to do that, it is totally separate. Just for reference it takes about 30 minutes of labor to change the CO setting if the dealer knows what he is doing.
My 17 is set to +45 but if I had easy access to it I would try +55. My 2012 is set at +60 right now but it is easy to change.

If you have a flashed ECU this might not apply.

It's flashed. So I should not touch the TB at all until the CO is done. That's what I'm getting out of this. Correct?

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[eemsreno]

It's flashed. So I should not touch the TB at all until the CO is done. That's what I'm getting out of this. Correct?

Sent from my SM-N960U using Tapatalk

You can adjust the TB any time regardless of the CO settings. I was under the impression that having it flashed done away with the need to richen up the CO. You might have to ask the person that flashed it if it still needs CO adjustment.

 

[magic]

I played around with the CO settings quite a bit on my 2013 when it was new. I did not see any improvement in the off idle response until I increased the CO settings to about +40. I have been running the bike with both cylinders set at +50 for a long time now with no affect on gas mileage and the plugs always look good. Bike runs better than it did new, but probably not as good as a flashed one.

 

[TenereGUY]

You can adjust the TB any time regardless of the CO settings. I was under the impression that having it flashed done away with the need to richen up the CO. You might have to ask the person that flashed it if it still needs CO adjustment.

Ok, thanks.
I was planning on doing the TBS and didn't think it would hurt.

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[Meterpig]

I have two items to cover here.

1) Airscrew adjustment to fix the off-idle stumble that some have complained about, especially in the California model.

2) Throttle Body Sync that will apply to all models. The TBS has to be done after the airscrew adjustment as part of the process.
I also installed pigtails to the ports to stay installed to make checking the sync later a simple process that will not involve lifting the tank. If you have to make adjustments, you will have to lift the tank to access the screw on the left, but the check is easy without lifting to see if a change is needed.

According to the Yamaha technician that I spoke to, the off-idle stumble and low RPM rough running issues are caused by the adjustment that Yamaha has to make to pass emissions. He said the airscrews are adjusted all the way in from the factory. The service manual says not to adjust the standard airscrew (the one on the right side with white paint on it). For this fix, you adjust both.

Here is the fix:

1) Remove side panels, and tilt tank up to gain access the throttle bodies.
2) The right Airscrew on mine was the standard with white paint. The service manual says not to adjust this one. For this fix, you adjust both of them three quarters of a turn out, (counter-clockwise rotation 270 degrees).
Once they are both rotated 270 degrees out, then you adjust the unpainted one in or out to do the throttle body sync. This puts the Airscrews in the needed position for smooth low RPM running.


I marked my screws with a sharpie ahead of time to be sure of the original location and to see what adjustment I ultimately made to the screws.

Here is the right side standard before adjustment.

Here is the left side before adjustment.

Here is my left side airscrew after the throttle body sync. I ended up having to adjust it back in about an eighth of a turn to get in sync after the adjustment.

The actual Throttle Body Sync is very straight-forward and is outlined in the service manual in section 3-8.
I did install pigtails on my ports to stay connected as I mentioned earlier.
You can see them in my pictures above.

Here they are before I put them in place.

The materials you need for this are:
1) about two feet of 5/32 vacuum hose
2) Two .1875" brass barb connectors
3) two 5/32 vacuum caps
4) One .1875" Vacuum "T" connector
5) three small spring hose clamps to ensure no vacuum leaks.

For the left port you cut three sections of tubing to 1.5", 3.25" and 6".
For the right port, cut one section of tubing to 8".

Assemble them as shown in the picture. Install on the ports and route as shown in the pictures.
When you do a TBS, pull the vacuum cap off of the hose barb and connect your manometer. After the sync, cap the barb and leave in place for the next time you need to check sync.
I suggest you use the small spring hose clamps at the two ports and the plastic nipple on the left side. I tried it without these first and got an engine light fault on decel from a vacuum leak.
A smaller diameter .125" ID hose would be better, like the small one that is removed from the left side, but I could not find that at my auto parts store.
You can also remove the pigtails and replace the original tubing and cap and access this once the tank is down. You can add the pigtails back without having to lift the tank.


This was an easy fix to the off-idle stumble and made a huge difference.
The bike actually idles along on its own now and will run in first gear at about 8mph with no throttle input.
I hope this helps.

thankyou for the excellent photos and write up. I was able to do my 2012 in 5 minutes.