Flat spot from hell after jetting

[mainlinecoffee]

Hey everybody. I got a 01 gz with stock carb six six sizes up on pilot jet and 140 main but I noticed that at any speed if under load if I snap throttle open it just flatlined and looses all power. If I baby it open it has power for days. I thought it would improve in warmer weather but no such luck...is it possible it is junked up from running fuel through a new gas tank? Someone said oil would build up in carb.