Engine weak above 4000 rpm

I have a 79 KZ 400 Ltd. I just cleaned the carbs and I think I did a good job since it starts perfectly and pulls better than ever at low rpms. However over about 4000 rpm it won't pull, seems like it is not getting fuel. This happens in every gear, with or without the air filter in place.

I adjusted the timing but it makes no difference. Did I do something wrong when cleaning the carbs? Is the float bowl level too low? Is it a valve adjustment issue?

Thanks for your help.

Check for kinks in your fuel line. I had a similar issue, @ about 6k on a KZ650. Had a longer a fuel line... snipped ~1/2" and all is good...

Also, got an inline fuel filter? If so, new or used? It's only $2-3 for a new one... please consider this.

What a good idea, I will check tonight for kinks. J

10-4... good luck. Also consider the filter...

Well I checked the fuel line, it is clear. What next? Maybe the petcock is bad? Would cleaning the carbs affect the float bowl levels? Thanks.

these old carbureted girls' fuel is gravity fed....Make sure your tank is venting properly...I had a TON of crud inside my gas cap's vent channels...They "breathe" through the keyhole in the cap...Not enough air in, not enough fuel out! Something to try, anyhoo!

Thanks I will try that next.

Check your timing advance and make sure the cam lobe rotates counter clockwise easily, and snaps back into position clockwise. If the timing is not fully advanced at 3500 rpm, the motor will fall on it's face.

Thanks for the suggestion, the timing advance is well-lubed and moves easily. J