Luhbo wrote on 09/21/10 at 21:08:06:

Then we are in agreement, because that is just what I said. Disable closed loop in order to *avoid* this! 

As a retired Standards Laboratory Engineer, I have to agree with raz.  In order to insure that the TB's are synchronised, you have to eliminate other means of compensation (the CylOffs table, and O2 sensor inputs).  Once that is adjusted as closely as possible, the O2 sensor(s) will "fine tune" any minor imbalances by means of the CylOffs table.  When I reversed the O2 inputs on my bike, the CylOffs table started to show large values.  I followed raz's advice, then put the O2 inputs back in proper order, set the O2 sensor input back to "both", and now the CylOffs table shows only small values.

OK, Not to argue, but to do a better job of explaining, (RAZ, correct me if I'm wrong!), here are the details as I understand them.  The O2 sensor(s) are the input to the ECU so it can adjust the AFR by changing the Injector Duration.  CylOffs is that compensation for the right cylinder.  When you change the AFR, it affects how that cylinder performs, and it will change the intake vacuum at the specific RPM where you are adjusting.  The pressure gauge attached to that cylinder will then show the compensated vacuum pressure.  This works, but as the TB's get more and more out of sync over time, more and more compensation has to be applied.  Since the engine is operating closed loop, you may or may not notice the difference, it's just a matter of procedural correctness.  I hope I did a good job of explaining the details.

Luhbo wrote on 09/22/10 at 18:34:36:

I'm not sure I understand your point. The OEM users already run open loop so they can just hook up the manometers and sync it. I can too, running open loop or not. But COnewbie should disable closed loop because he has two sensors. I may be wrong, it's just a gut feeling.

COnewbie wrote on 09/23/10 at 04:46:17:

I think you got what I meant but like I said, I'm not sure we are right. After all, the vacuum is produced by the rotating engine, more or less regardless of individual A/F's. Maybe this is how you see it, Luhbo?

An extreme example would be this: Sync your TB's. Then kill one of the cylinders, eg. pulling the wire from its injector. Now, are the TB's still in sync while the engine is running on only one cylinder? I can't believe it would be.

I just imagine that if you have imbalance (i.e. a mechanical imbalance), the individual closed loop can compensate a little for it, and this will make real (mechanical) sync harder. Maybe this is not much of an issue, but one thing I'm 100% sure of: Syncing in open loop will not hurt.

I tend to think of extremes in order to understand smaller things but maybe that was too extreme 

The more I think of it, the more I believe you are right. If it's an issue at all, it's probably academic.

I believe you're right, but with this caveat:
If both TB's have the same opening, and all four valves are adjusted exactly spot on, then both cylinders (assuming perfect sealing of the piston rings), will have the same A/F, and CylOffs would be expected to show 0 throughout the CylOffs map.  The reason I mentioned the valves is because the valve lash affects the timing of the intake and exhaust cycles.  Less lash makes the timing earlier, and more lash makes it later, which can affect the A/F if there is overlap with InjDur or SpkAdv.  That's MY guess!