Z1Driver wrote: But above 60-80 mph highway cursing speed
I have a cursing speed too. I believe when my 900 was running better at almost WOT than at WOT, I adjusted pilot air to fatten it up a bit. I was getting a hesitation at WOT and if I backed the throttle off a bit it would smooth put and run better.
There should really never be much change in mixture from 3/4 throttle to WOT since there will be no sudden changes in the needle and it's predominantly main jet and needle that control things there. A fuel flow issue might cause it, but seems unlikely since just off WOT runs fine.
One thing that can cause this, and often is a problem on 550's is the throttle stop screw. On the 550's with mechanical carbs, the throttle stop screw is often set to stop the throttle at a point beyond where the slide is 100% open. This means that after the slide reaches fully open, which is where the slide is flush with the roof of the carb throat, you can still pull it open a little farther. For that little extra pull, you are adding more fuel since the needle is raising and letting in more fuel, but you cannot add any more air because the slide is already past fully open. This means the mixture takes a sudden nose dive towards rich and you will lose power.
On a stock 550, it's not so drastic. When you hold WOT for awhile and the bike comes up to speed, if you start to roll the throttle off very slowly, you will get a sensation of accelerating. Only after you roll off a little more will it start to slow down.
I'm not sure how the 900 carbs are setup, but if there is a throttle stop adjustment, you may want to make sure the slides are not opening beyond full open.