Power is intermittent...wont reach 25mph

Hi

Ive got a 1998 yamaha neos. Just had it on the tacho and the revs maxed out at 9700rpm...idles as sweet as a not and throttle very responsive. Took it for a spin last night and there is no power under load, hardly reached 25mph let alone 40+.
It never stalled but the power drops off then comes back...drops off then comes back...you get the idea.

Any ideas please?
Flooding maybe?
Ive been told it may have had a big bore kit fitted. I dont know myself. Its a phbn carb with 72 main jet. No filter in airbox.
Thanks in advance

 

Put the filter back in to start with and go from there!

 

Thanks for reply. Will do that