carb question (Holley)

The power valve is probably blown out due to a backfire throught the carb at one time. It doesn't take much, a hesistation when coming off idle when cold & poof! More probable too since you have no choke to help it warm up either. Cutting the choke horn off (assuming it was done correctly & not butchered up) shouldn't cause the power valve to open early. You also want to make sure the idle circuit isn't blocked otherwise that will cause the fuel to pull over.

I'd put a new power valve in it & clean out the idle circuits real good & go from there.

Funny, I had damn near the same set up on my '83 Mustang GT too. Probably put a 1/2 dozen power valves in that car.