Been having a bit of bother with the YZF lately. Bike starts fine, idles fine & runs fine up to 4-5000 rpm. Beyond that point it feels flat & struggles to rev out. Rev counter needle jumps to 9000 rpm, drops to 3000 rpm & then to zero. Sticking EXUP valve? Fuelling issue? Any ideas?...I know the rev counter movements are a sort of diagnostic code but what does this particular movement signify? Any help appreciated.

Take a look to the EXUP valve:

1. Is the servo motor properly plugged?
2. Start the bike and look if the servo motor moves from its position.
3. Clean the connections with dielectric grease and try again.
4. If the symptoms persist, open the servo motor and check if the wires and the small gears are OK.

The servo motor must be always connected to the ECU.

A friend of mine had a similar problem