'91 FZR isnt running smooth

[primus92]

ok well the story is, that over the past two weeks i took my radiator off, and changed my spark plugs. and she ran perfectly fine, rpms was doing great and everything. i rode her a for a little bit on the open road, to see how she would do, and i was doing 45 in 3rd gear, and when i gave it throttle she didnt seem to want to jump into any higher rpms above 5 to 6 thousand. switch to a lower gear, and still same problem, i slowed down to a complete stop, and she just died on me, finely got it back to the house, in my truck. and figure that ill let it sit to cool down some. i checked my coolant level, and it was low. at first i thought she just got too hot and died out, cuz when i put my radiator back on, i thought i might of trapped some air in my block so coolant couldnt pass through. i started the bike today and after a few cranks and some throttle. she fired up, after getting her warmed up,i backed the choke off, and gave it some throttle turns and the bike seemed really hesitant when throttle was givin. and she would start to bogg down after 5 thousand rpms. its like she would try to pull air, but doesnt want to make the power. after checking out the bike looking over it, the only things i noticed was some cracks in the boots under the carbs. took the carbs off, and the cracks didnt seem to break through, didnt know if that mattered or not, or if cracking is cracking. does anyone have an idea, why my FZR is acting up this way