Is exhaust back pressure the culprit here?

RedFish said

I'm thinking fuel delivery too, although I question the exhaust being the cause.
Had the car been on a road trip before going to muffler shop ? Or did this road trip get the intake and carb a lot hotter than it had been before ? If I'm right a stone cold start will show no problem.

Click to expand...

You might be onto something. I went out to the garage this evening and it started just fine and idled smoothly like it has been for weeks. Stone cold start...depressed accelerator once to give it a sip and set the choke. Popped right off, had to give it just a little coaxing to settle into a nice even idle. Let it warm up, killed it, waited a few seconds, and it fired right up again.