how to fix my petrol problem?

hi i have a derbi senda 04 model with a vacuum petrol pump, i recently changed my carb and i thought the vacuum tap was knackered as it would flow without the suction pipe on the carb, but now its stopped flowing and i cant find where abouts it goes on the carb. if i suck on the pipe petrol will come thru i just cant seem to find where the suction pipe goes on the carb.. any help would be appreciated cheers