ZZR 250 intermittent prob.....

About a week ago I was riding along at about 60ks and changed down gears for a corner, when I started to power up to exit the corner, the bike felt like it was lacking heaps of power. So I wound the throttle right on and slowly it picked up to normal again. Next corner, clutch in to down shift and the engine dies and wouldnt start again. >:(
I got the bike back from the mechanics today and took it for a run out of town. The mechanics pulled off the carbies and cleaned them, emptied the tank and cleaned it out (apparently the carbs were filthy), new plugs and fuel filter. Anyway, bike ran fine for a few ks then felt like it was lacking power again. I hit the hundred zone and gave it a bit and could only get to 120ks and the engine was feeling really 'flat'. So i pulled over and it died again and wouldnt start. After alot of swearing because I had no phone signal and was about 10ks out of town, i started pushing it back and came to a hill, so I tried to clutch it in 2nd which got the engine just chugging over with full throttle. Eventually it picked up speed and ran fine into town and back to the bike shop.
The mechanic took it for 2 rides and found no problem and said he got it to 160ks which is about normal. He suggested possibly a kink in the fuel breather line but I deliberately kinked the hoses but nothing happened...
WTF??? Has anyone else had this problem?
Sorry about the length, but I wanted to put as much detail as I could... Any help is REALLY appreciated!!!!!
Thanks!!!!!
I got the bike back from the mechanics today and took it for a run out of town. The mechanics pulled off the carbies and cleaned them, emptied the tank and cleaned it out (apparently the carbs were filthy), new plugs and fuel filter. Anyway, bike ran fine for a few ks then felt like it was lacking power again. I hit the hundred zone and gave it a bit and could only get to 120ks and the engine was feeling really 'flat'. So i pulled over and it died again and wouldnt start. After alot of swearing because I had no phone signal and was about 10ks out of town, i started pushing it back and came to a hill, so I tried to clutch it in 2nd which got the engine just chugging over with full throttle. Eventually it picked up speed and ran fine into town and back to the bike shop.
The mechanic took it for 2 rides and found no problem and said he got it to 160ks which is about normal. He suggested possibly a kink in the fuel breather line but I deliberately kinked the hoses but nothing happened...
WTF??? Has anyone else had this problem?
Sorry about the length, but I wanted to put as much detail as I could... Any help is REALLY appreciated!!!!!
Thanks!!!!!