I'm going to assume you're in Oz, not that it matters but always nice to know where everyone is.
Think of the fuel system as being one continuous tube which runs between the fuel filler on the tank to the jest in the carbs. At any point between either end there is potential for fuel to escape. Even a minute weep will cause a smell.
So to find the leak, start at the top (the tank) and work your way down the tube to the carbs. Check the seal around the filler cap isn't damaged for starters. Check that the tank breather isn't blocked.
I've had a few problems with petrol leaks on both my canes, firstly starting with the tank its self and then on the second bike, the fuel tap had an internal leak through the seals around the valve shaft resulting in petrol leaking out through the tap body. It took me quite a while to suss that one out and the only cure was to replace the whole tap. Replacing the diaphragm made no difference.
Take off the tank and check there's nothing weeping from under the front mounting point. If you detect a petrol leak around this area of the tank you're probably going to have to change the tank. Trying to seal it from the inside is hit and miss and even if you do seal it the chances are that it'll start leaking again as there is a lot of flex between the tank and the bracket when the bike's in motion.
You may be lucky, it could just be a rubber hose further down from the petcock.
Its a process of elimination. Hopefully it'll be pretty obvious.