^^ speaking from experience the centrifugal advance in a carby distributor needs to be re-tuned for specific range spark advance where you would like to hit nitrous, also adding the correct fuel to compensate the additional oxygen you just dumped in.
the case in Pakistan is - collect pocket money or beg daddy to give some money, go to perf shop, install MADE IN CHINA super duper NOS with 2 dozen stickers, drive off, blow your engine and have ustaad rebuild it.