Hello dimitris_mc21 and welcome to the forum.

Grey plugs would normally indicate a lean mixture. The motor will always find it easier to rev in the low gears as it's under less load, even if the mixture is incorrect.

Symtoms similar to fuel starvation in the higher gears could be a lean mixture or incorrect float levels.

If the bike is fitted with the HRC jet kit, then the X-piece should be left open to air, as described in the tuning section.

Specific jetting is not allowed to be discussed on the public forum. There is a special section in the Members Area where you may get some advice on specific setup.
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Andy.
NSR-WORLD.COM

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