spark plug heat range

What does the heat range of a spark plug mean any way?
Cause what i have is a spark knock problem that I have only encountered this season. So here is what i did to get it. Last season i pulled to a stop light and the engine stalled HMM. wtf. got it started off i go next stop light same thing HMM. wtf. so I find the culprit (spell check) on of my air/fuel screws kept backing out making it run to rich which is what it was always doing anyway.
So i find some rubber hose that fit the screws and into the hole of the float bowl (holley carb). I have finally got it running some what right no more fuel smell anyway plugs running a little white (lean) right? So the only other thing that i have done is change the spark plug. Local parts store didnt have the ngk#7 so I went with r44ts and now i have spark knock. also my dizzy is msd locked and is set at 32 deg. Oh and the only time I get this is when i put my foot int he carb (full throttle).
12.5 compression with race fuel.
950 proform carb
I have already started jetting the carb up in sizes and the spark plugs are getting darker and seems to be running a lot better on the bottom end and even mid range but full throttle spark knock. so my question is would the spark plug make that much of a diff

To add to Denny's post, Remember that NGK reverse's their numbers. Higher is colder. Lower numbers are hotter. FYI. (Thank's Denny, didn't mean to step on your toes).

so a hotter plug could cause pre ignition

ok Denny thanks one more question then.
will this change the air/fuel ratio? i mean have i been barking up the wrong tree here will it run richer with a colder plug.

they had cork gaskets and they were wore OUT badly so thats what i did i dont know if i like that spring idea Oh thanks for your help Denny

I run a NGK #9 plug in my bike. It will burn a hole in the piston if I run anything hotter.

Yes, They sell the "corks" by themslves. Usually have to order them but worth the wait. Thanks Denny for bringing up the springs. I forgot about those from the olden days. (not to make any of us any older....:LOL:)