carb issue
How many turns out do you have the mixture screws?
Try 2 rounds.
How far open are your butterflies?
The transfer slot should barely be showing looking from the bottom of the carb up.
Sometimes the butterflies have too much of the transfer slot uncovered which will make it run rich at idle then go very lean when you whack the throttle because it already using part of the transfer fuel supply while idling.
87-90 jets squared with no PV's should be close on the jetting
Is timing locked @ 38 or do you have an advance in the distributor?
May try locking it, if it's not already.
Have you checked for a vacuum leak?
Good Luck, Mark