Kawasaki z250a bogging at high revs

[Sparky700]

hi all I'm after a bit of advice. I've just restored a barn find 1981 z250 twin which is a great little bike. She's purring like a kitten but won't go past 8k. Carb has been thoroughly cleaned and I managed to source some rare carb holders which improved it slightly. Timing has been checked and rechecked. I'm running out of ideas. One thing though is if I give it some choke she will blast past the red line no probs. Any suggestions?

[Easy-X]

Sounds like you're hitting a fuel flow limit. Assuming the carbs are actually jetted correctly I'd be looking at tank, petcock / fuel valve & fuel pipe blockages.
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[stinkwheel]

Pulling through a flat-spot at wide-open throttle when you apply the choke is a sign of lean running. If you do a plug-chop at WOT, I'd bet it's white and scorchy.

Is it on original airbox and filters? Needle position correct?

You may need a bigger main jet and/or different emulsion tube... The question is why?
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[jaffa90]

If the plug chop (colour) is showing lean then it`s more fuel or less air as in a denser air filter (part choke).
Providing no unwanted air going in.

[Sparky700]

[Sparky700]

[Sparky700]

[Robby]

How is the fuel flow out of the tank? If it was filthy and you cleaned it, all the remaining sediment (there is always some left) will collect around the lowest point in the tank - the reserve setting on the tap.

If you remove the tap you'll probably find some crud around the fuel tap hole.

[Sparky700]