I have a 1995 s-10 Chevy Blazer with a 4.3 vortex engine,4wheel drive,auto trans. My question is why won't it start ? The only way to start it is to prime it first with gasoline or carb cleaner.

First step is fuel filter, next fuel pump. Last is regulator but when it goes bad it leaks fuel into the engine and floods it, starter fluid would make it worse

You could be having a fuel presser regulator leak down, with your fuel pressure gauge connected, you can jump the fuel pump wire at the relay 87- to 85 I think or just turn the key on and cyclical the key on - off (4 times) leave it on for 10 sec at each time , check the fuel reading still under 50psi? No start condition for the low psi or will tremble and die out. Replace the fuel filter only $15 doll- hairs, check if your getting a restriction and a fuel psi reading if not on spec.Next .... most likely the pump is going bad or the ground wire connection. I would add a secondary ground wire to the fuel pump ground wire and splice it in, replace the pump! Make the ground wire close to the pump like a under body part , polish the metal with sand paper and add a bolt to attach grounding wire to with new fuel pump. gives you better fuel pressure as the pump will run with less resistance to ground, giving it more use of the power provided, it's a good step. hope you get it.

Check voltage regulator

I had that problem it was the spider fuel injection