Have you changed the engine breathing characteristics from stock? Air filter, Exhaust... stock?
The turnouts on the bike in your avatar are likely less restrictive than the stock ones. This lack of restriction will help evacuate the cylinders at high RPM and require more fuel to make optimimum power. High gears / high engine loads and throttle positions approaching wide open settings, demand the most power output from the motor. Your symptoms do sound like skimpy fuel ratios. But, there is not enough data for a conclusive determination.
Do a full and complete tune up.
Install brand new plugs and perform a plug chop after a run with throttle wide open.
Read plugs and proceed using this information.
You can also get proper information by utilizing a Dyno facility that can instrument your bike, load the engine in any gear, and sniff the exhaust for combustion by products. This will tell you about mixture setting at any throttle position, and be a guide for corrective changes.
If I assume that all your tune up items are perfect, carbs clean and balanced, a clean air filter and exhaust in a design you have no plans to change, then, I'd guess you are probably looking at raising the main throttle valve needle and possibly a larger main jet.
If you fiddle with the carb jetting before you stabilize the other items, you may well increase the practice time you'll have with corrective jetting procedures.
Cheers,
