2000 Suzuki Katana is lacking power between 9000 and 6000 RPM?

Question edited for a lot more clarity, full 'year make model'..
Question moved to model category.

Of course if it is fuel injected, but you are near the crossover year. Do you see carbs?

https://www.google.com/search?q=2000+Suzuki+Katana+600+does+it+have+a+fuel+pump

https://www.motorcyclespecs.co.za/model/suzu/suzuki_gsx600f_katana%2000.htm

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No you can't. You will burn out the switches. Just buy a used kickstand relay for $15 and a flasher relay for $8.71. There appears to be two relays, one for flasher and one for relay. When you write 'flasher/kickstand relay', you are indicating one relay does both because of the slash /

https://www.google.com/search?q=2000+Suzuki+Katana+600.+flasher+kickstand+relay

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The power regulator may be at fault.

1. GSX 600F Katana - Motorcycle Specs

   www.motorcyclespecs.co.za/model/.../suzuki_gsx600f_katana%2098.ht...Suzuki GSX 600F Katana ... Wet Weight, 229 kg / 504.8 lbs. Fuel Capacity. 20Litres ... The original GSX600F was launched in 1988 as a sportsbike. At that time ...

lack of fuel,float level wrong or blocked jets

Remove the carbs from the bike, then remove the bottom of the carbs to gain access to the floats. You want to flip the carbs upside down and set them level by bending the tabs.

Displacement: 599.00 ccm (36.55 cubic inches)
Engine type: In-line four, four-stroke
Power: 86.00 HP (62.8 kW)) @ 11000 RPM
Torque: 58.00 Nm (5.9 kgf-m or 42.8 ft.lbs) @ 9500 RPM
Valves per cylinder: 4

IF EVERYTHING ELSE IS OK, SOUNDS LIKE YOUR IGNITION SWITCH COULD BE GOING BAD.

your carbi will need a clean first and tune as well . air filters will need cleaning to allow full air intake .
Make sure to have clean spark plugs too

sounds like a bad diaphram in one of the carbs