Stumbles/Hesitates at anything more than 1/3 throttle

'88 Corolla Deluxe. Just bought it. Runs well and idles smooth. When cold, she runs fine and can give as much throttle as you want. Once hot (normal temp), give it more than 1/4-1/3 throttle to accellerate and it's like a switch - total loss of power. Back off a little bit and you have power.

Any ideas? Well maintained engine with regluar oil changes (verified by inspection when I pulled the cam/valve cover). Runs very well, just looses power like a switch when hot.

Passed Ohio smog check with very low emissions a couple days ago.

So no one has an idea?

How is the oxygen sensor used on the 4AF engine with 2bbl carb? How does the computer use the sensor info to control the carb?

Given this problem only happens when the engine is up to operating temps, I am beginning to think the computer is controlling the feedback carb incorrectly and compensating what it thinks is a problem when there is no problem.