my 1990 kick,when cold startup it seems to run well, no stumbling when under throttle but when it warms up it has a very bad dead spot right when you take off under load, when it stumbles i can pin it and it just about dies till i let off and apply power slowly, when revs get up it clears up and goes well till next time i shift, any ideas, thought off plugs/wires but why smooth when cold/rich mode??