I notice that some think a TBS is more effective if you do it at 4000 rpms instead of idle speeds, but it would seem that the throttle position required to make 4000 rpms would be far less in a no-load situation than when actually riding at 70 mph making the TBS at a 4000 rpms somewhat meaningless. True or false?
True and false. It is true that the throttle position under no-load is considerably less than the throttle position under load. It is false to assume that it has no bearing.
For those that are unfamiliar with the linkage between the throttle bodies, the throttle cable is attached to the #3 throttle shaft. The #4 throttle shaft is connected to the #3 throttle shaft by way of two little springs. Similarly, #1 is connected to #2 and #2 is connected to #3. So when you twist the throttle, the cable does not open the butterfly on #1 directly. It opens #3, which applies pressure on the springs of #2 and eventually opens it, which applies pressure on the springs of #1 and eventually opens it.
Opening the throttle, even without load, takes the butterflies off the stops and puts tension on the springs, settling everything into the position they will assume at 4,000 rpm under load. So while the actual throttle opening used during the synch is not the same, the effect is.
Why wasn't this done at the factory? I'm sure it was. The problem is that springs fatigue over time and each spring fatigues at a slightly different rate. These things are extremely sensitive -- I love showing people how just the mere weight of the screwdriver resting on the adjustment screw makes a difference in the vacuum readings. So, while it was undoubtedly perfect in the factory, things slip out of adjustment over time.
BTW: I personally do it around 3,000 rpm. Others have since suggested 4,000, reasoning that 4,000 is a more common resonance point. I don't think the actual rpm makes the slightest difference -- what is important is that the butterflies are all off the stops and the springs are at operating tension.
I will close with the same warning list I gave when I originally suggested it: This is NOT the Yamaha recommended procedure. Yamaha does not authorize fiddling with those screws. Yamaha puts a dot of paint on each screw so they can tell if you fiddled with it. Do this at your own risk. Just because it worked for me does not mean it will work for you. If you bugger up your bike, I wasn't there, I didn't do it, He only looked like me and I don't know her.
Etc.