Popping from passenger side exhaust when first started

this is on my 302 with the kaase canted valve heads the last two times i started it it was popping like a fire cracker it seems like from just one cylinder then about 20 seconds it clears up and is fine. I'm wondering if its a sparkplug i have the autolite ar3934 gapped to 45. The reason i'm leaning towards the plug is it clears right up and is fine after that. i know on my yellow mustang with the 472 once in a while when it first starts after sitting for a while it seems lazy at first then clears up and sounds better and revs better so maybe its the same on the 302 o and it was in the low 30's out when started. Any other ideas ? maybe plug gap too big?

Maybe you fouled one out. It may clear up and idle fine, but when you put a load on it, it might start missing again at higher rpms. I have had this happen with resistor plugs.

I had a similar problem once it popped through the exaust until it started to warm up and it was a bad header gasket. once it started to warm up it sealed itself.

Bad Plug? Valve Sticking?

Thanks for the replys i'll check the plugs as far as the gap .045 should be fine you think ? using all msd ignition.