Throttle Body Sync Questions

[boxerpaul]

Thanks in advance for your help.

I've just tried my first throttle body sync. (I adjusted the valves just before winter storage)

I made a manometer to do this based on descriptions I read here and other forums.

My questions are:

Leaving one side alone as a reference/control and only adjusting one side seems to make sense to me. Am I completely incorrect about this?

I can never get the water levels to line up completely, there is always a little fluctuation. Are they supposed to be dead even with no movement at a given RPM? (I was using ~3000 as my set point - please correct me on this if this was incorrect)

The water levels at idle jump back and forth a lot, and I think this is ok, however they're not really at the same height, there is usually one side that is higher at all times (idling) and they jump up and down at their respective levels. There was a time during the process when they were more even, but they were out of whack while revving.

I can't for the life of me snug down the locking screw tightly without throwing off the adjuster. How snug does the locking screw have to be?

Finally, is there any harm that can be caused if I've upset the balance worse than before other than the engine running a little rougher?

Your help is much appreciated!

[deilenberger]

Thanks in advance for your help.

I've just tried my first throttle body sync. (I adjusted the valves just before winter storage)

I made a manometer to do this based on descriptions I read here and other forums.

My questions are:

Leaving one side alone as a reference/control and only adjusting one side seems to make sense to me. Am I completely incorrect about this?

Correct. The usual adjustment is done on the right side TB. That's a holdover from the R1100 engine where touching the left side was sort of verboten.. it was the reference side. Not as critical now that our engine computer can "learn" the throttle-position-sensor, but it is easy to get to, so I would stick with the right side.

I can never get the water levels to line up completely, there is always a little fluctuation. Are they supposed to be dead even with no movement at a given RPM? (I was using ~3000 as my set point - please correct me on this if this was incorrect)

A water manometer is going to be way sensitive. Using a TwinMax on max sensitivity, I'm happy if the overall engine range doesn't deviate +/- 1 division from 0. You might try replacing the water with engine oil - the more viscous fluid will damp the motion better, and also won't damage the engine if it's sucked in by accident (and that DOES happen..) Many people also add a restrictor of some sorts in each of the vacuum connection lines to help damp the manometer.

The water levels at idle jump back and forth a lot, and I think this is ok, however they're not really at the same height, there is usually one side that is higher at all times (idling) and they jump up and down at their respective levels. There was a time during the process when they were more even, but they were out of whack while revving.

You shouldn't even consider idle readings since the balance at idle is under the control of the computer. They rarely are even at idle - the ECU is adjusting them individually via the stepper motor bypass passages to get the best idle. Personally it doesn't do a great job, but since I don't ride at idle, I don't worry about it. The TB is most sensitive at about 2,000-2,500 RPM. That's where I set it. Above that, differences aren't as significant since the differences are small compared to the total amount of air going through the TBs.

I can't for the life of me snug down the locking screw tightly without throwing off the adjuster. How snug does the locking screw have to be?

Snug. 4" wrench finger snug. You may find it useful to hold the adjuster gently with a needle-nose pliers as you tighten the locking nut. You also will gain a feel for how much tightening it actually changes the adjustment, and pre-compensate for this.

Finally, is there any harm that can be caused if I've upset the balance worse than before other than the engine running a little rougher?

Not a lot of harm. The O2 sensor should keep a cylinder from running way too lean and burning things. The vibration might be annoying.

Your help is much appreciated!

A FWIW or two:

1. I've never needed to rebalance mine IF I get the valve adjustment PERFECT (anally perfect) before checking the balance. Make sure you're not compensating for an inbalance caused by a poor valve adjustment.

2. If you're a BMW-MOA member - the Hexhead DIY section has an article on doing a TB sync with photos and hints - done by an outstanding author. I highly recommend it.

[boxerpaul]

Don, thank you very much for answering all of my questions. People such as yourself are the reason this forum is such a great place.

I'll have to look into becoming a BMW-MOA member.

[rtallent]

You shouldn't even consider idle readings since the balance at idle is under the control of the computer. They rarely are even at idle - the ECU is adjusting them individually via the stepper motor bypass passages to get the best idle. Personally it doesn't do a great job, but since I don't ride at idle, I don't worry about it. The TB is most sensitive at about 2,000-2,500 RPM. That's where I set it. Above that, differences aren't as significant since the differences are small compared to the total amount of air going through the TBs.

Don -- Just did TB sync (really easy on this bike!) but one question relating to above. I didn't expect the TwinMax needle to sit relatively still at idle like it does at higher revs, but I DID expect it to hover around 0, not around, maybe 2.25! (In other words, it varies +/- 1 to 1.5 divisions or so but with roughly 2.25 at the center, not 0). Is this also considered normal? I really don't want to spend $300 on a GS 911 right now if I can help it and I don't have time to spend a whole day going 250 miles to my dealer to take care of this now either, if it needs taking care of. The bike rides great and even feels ok at idle. What's your take on this? As always, many thanks.

[deilenberger]

Bob, I'm not sure exactly what you mean.

You may see some rapid movement around center on max sensitivity if you don't have restrictors installed (does the TwinMax come with them?) If you do see this - it should still be centered on zero, so if you're seeing 2.5 divisions of movement total - I'd expect 1.25 divisions on either side of 0. This should go away as the engine speeds up (the integration time of the twinmax damps it out..) Restrictors are simply something in the connection that slows the airflow - through a small hole usually. Think of it as damping.

[rtallent]

Bob, I'm not sure exactly what you mean.

You may see some rapid movement around center on max sensitivity if you don't have restrictors installed (does the TwinMax come with them?) If you do see this - it should still be centered on zero, so if you're seeing 2.5 divisions of movement total - I'd expect 1.25 divisions on either side of 0. This should go away as the engine speeds up (the integration time of the twinmax damps it out..) Restrictors are simply something in the connection that slows the airflow - through a small hole usually. Think of it as damping.

Thanks, Don, I guess that answers it. The rapid movement you describe is what I'm seeing (and what I expected), it's just not centered around 0, it's centered around a point way to the right (a point roughly between 2 and 2½). (The movement does go away with increasing rpm and is quite steady at syncing rpms.) I guess I'll have to invest in the GS 911

[tmfirestone]

This may sound like a dumb question but where is the adjustment screw? I have checked mine and the right side body has more vacuum than the left and I need to adjust. I do not see the Big Brass Screw mentioned in the adjustment procedure in the ADVrider.com Hall of Wisdom. Thanks for your help!

[hjsbmw]

This may sound like a dumb question but where is the adjustment screw? I have checked mine and the right side body has more vacuum than the left and I need to adjust. I do not see the Big Brass Screw mentioned in the adjustment procedure in the ADVrider.com Hall of Wisdom. Thanks for your help!

There is none. Could they be talking about an oilhead? You adjust the throttle cables directly. If your right has more vacuum you have to lessen the tension in the right cable, or turn the right cable adjuster clockwise. I think it is said that one usually adjusts at the right throttle body, but I don't know why. I am sure someone does. So, assuming I am right, if your left side had a higher vacuum you would still adjust the right to compensate for that.

[rookie]

Here's how I did it: Used a small diameter transparent tube that fits snug over the TB nipples Use a long enough piece (about 3 meters or 9-10 feet). Put about 1 meter length of water in it. Pinch the tube closed then start the motor. Slowly release the tube and then do the sync (right side only ) at about 2500-3000 rpm and you're done . Remember to do the valve adjustment first . She's now running smooth .