sputtering

[provs240se]

i have a 1993 turbo KA. when i fire it up it runs great pulls fine and everything, but once it warms up to the middle of the temp gauge it suddenly breaking up... Its hard to describe but it sounds like the timings off it sputters and bogs down and then eventually it stalls and work right until it fully cools down, Its really got me stumped..... thanks in advance for the help.