for starters you need to be running an AR3932 Plug and close that gap to 25 for starters.
Next have someone pull the trigger on the Nos ( just test the selenoid)..make sure Nos is not live nor fuel or Nos is dumped in motor.. while car is idling (3k) see if timing is being pulled out ( with timing light) when trigger is pulled...you will see it back up on the balancer.
i can tell you have not flowed the Nos by your post...thats ok many do not know how to properly flow a (wot) Free flow...i don't know if i can explain it good enough for you in a post...
What concerns me next is what kind of fuel pump you got supplying the Motor and Nos ?..then what kind of igintion you running ( crank trigger) ???
if your not running a BG 400 or Magnafuel Prostar 500 or some comparable fuel pump..chance are you don't have near enough pump to support a 300 shot on a 502 ( in one pump)...
my advise to you..is don't run any more NOS until you know for sure rthe things i have posted...youll burn that bad boy down in a skinny minute with a 250/300 shot..
there's alot more to running Nos Safely than what one thinks ?
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Bjuice..
"I'M YOUR HUCKLEBERRY ! "