i have an 84 z28 with a chevy 350 in it when i bought the car the guy had no plug wires on it so i went and bought new wires and put them on along with new plugs cap and rotor it has an hei ignition i kno i have the right firing order the one im using is 18436752 and ive had the engine at tdc and it will fire up but runs like crap i have to keep it at wot in order for it to run and when its running its running like crap and as soon as i let off the throttle it dies and belches fuel up thru the carb...i am so confused on what to do so any help would be greatly appreciated.

 

I hope you mean 1 8 4 3 6 5 7 2 looks like you have 5 and 7 crossed.
try that first it should fix the problem

 

Also, there are TWO TDC's - one on the compression stroke, and one the exhaust stroke - you HAVE to have TDC #1 piston on the COMPRESSION stroke, the make sure rotor points to #1 plug wire on cap, then follow firing oder on cap clockwise for other wires..