Damned clever, these Japanese! I should have guessed that they would use a needle, most of the euro peds seem to live withou and and depend on air box restriction to enrich the mixture at wider throttle openings.
With a needle, you have the option of moving the clip on the needle to a different groove, normally there are 5 grooves. The top groove is the leanest setting and the bottom groove, closest to the point, is the richest setting.
Unfortunately, your problem is at full throttle, when the needle is typically all the way out of the needle jet. You may want to verify this when you check that the slide rises up all the way. If the needle can be set low enough, you may be able to lean the mixture at full throttle, otherwise, the main jet and float level are the only things you can change. If your carb has a hinged float, it is fairly simple to lower the float level.
The normal carb adjustments, in order, are:
Float level, to establish the correct fuel supply.
Main jet, to control wide open throttle mixture.
Needle position, to correct mid-range mixture.
Idle mixture and speed adjustment.
There you go, have fun.