I have a stock 86 z28 with a E4ME computer controlled quadrajet. The car runs great most of the time, but on hot days the car occasionally stumbles and hesitates really bad when the secondaries kick in. After that, the car hesitates and surges even when part throttle (primaries). But once you get up to crusing speeds, runs great. Idles fine too. Sometimes it clears itself out and is ok after and sometimes runs crappy until it cools down again. The problem only seems to start when the secondaries open and it doesn't always happen. Electronic problem with TPS or mixture solenoid or what??? Any suggestions?????

 

Could be a hot fuel issue. At idle and cruise, the computer is adjusting the mixture ratio. At WOT, you're in mechanical open loop mode, and hot fuel is not as dense as cool fuel. May also not be enough being supplied to the carb due to heat.

An electronic problem with the ignition isn't unlikely, either.

 

Yeah, completely stock factory set up with the fuel lines. All of the rubber insulation is still there on the lines-but that thought did cross my mind. New coil, plugs, wires and ignition module too so probably not that either but thanks.