odd air leak symptoms. 02 gz250

[tunil]

Hi everyone, first time poster here. im a fairly experienced motorcycle technician but havent had much experience on this 2002 gz250.

The symptoms seem a lot like a simple air leak but not really. It runs fine when i first start it up, no choke, itll hold idle for 10 minutes if i let it sit there. As soon as I take it down the street a mile and back it starts acting up. It revs high for 30 seconds after releasing the throttle and eventually slows down returning to a slow idle, usually stalling. So I replaced the intake boot with a new one as well as the sealing o-ring. Also replaced the vacuum line to the petcock. I did a full teardown of the carb to clean it just in case. New spark plug and air filter too. But it still does the same thing.

This ones got me kinda stumped. Any help is greatly aprreciated.