It depends on how you have your distributor timed in relation to your engine, but on mine right now #1 & #2 plug wires are the ones closest to the driver fender. If yours was like this then you are possibly pushing the cap a little closer to the rotor, thus reducing arc gap there. If that is the case it sounds like you have a weak ignition. Like in need of points and capacitor, or new coil. The temperature thing could be the coil. My 66 Mustang back in high school (God rest her soul) had it's coil go bad, and it started misfiring as the coil warmed from the current in it.