Hey all,
I have a FZR that runs and rides great but around 5000 RPM it has a serious flat spot and a noticeable loss of power. Also, it idles fine once warmed up at around 1100rpm but sometimes when I stop for a light it will idle so low it'll cut out.

Is this something to do with the Exup valve or is it more likely to be a carb issue?

Thanks in advance!

A couple of things:
Clean the carbs and renew the fuel filter. If you're doing this check the needles looking for any polished ares that would show the needle is touching the emulsion tube.
When the carbs go back on you'll need to check they're balanced.

Exup. When you turn the ignition on you should hear the "weep weep" noise of the exup servo cycling open / closed. It's best to see if the valve needs adjusting, the tricky bit is getting the chrome cover off the exhaust collector box the bolts are usually seized so be warned you might need to drill them out. With the cover off you'll see the exup pulley with 2 prongs, you should be able to put a pin/bolt between them and into the hole behind them. If not slacken the cable adjusters up by the servo, put the pin in and use the adjusters to take the slack. Only do this finger tight, you should be able to squeeze the cables together behind the pulley by 2-3mm. Take the pin out, turn the ignition on see the pulley cycle and return to the correct position - do this a few times. Check the cables haven't frayed, if they have you can get a repair kit from Venhill.

I think it's more likely the carbs if you're not confident with it find a dyno (rolling road) tuning shop to clean and set them up. This isnt cheap but it will be done properly and your bike will run a lot better after.

Did you ever sort the carb issue?