cavi mike is exactly right about the tickler.
if the bowl is empty, fuel will flow into it as long as the needle & seat isn't stuck closed. holding the tickler down at that point does nothing because the float is already down and the needle & seat are already open.
the stock petcocks (still funny) are **** and they are a very basic design with a little rubber diaphram inside....they flow very poorly.
the best and easiest thing to do is remove the petcock (giggle) all together.
go to the hardware store and get yourself a brass hose fitting and screw it into the tank in place of the petcock (yep, still laughing). Take that petcock with you to the store so you can find a brass fitting with hose barbs on the end. The brass fittings have the same threads, just match the size to the threads on the petcock.
Then, get yourself an in line fuel shut off valve (that sounds better than petcock) for a lawnmower. you can get these at almost any auto parts store or hardware store for a few bucks. (i know that autozone sells them) this eliminates the crappy in-tank petcock all together, and the fuel will flow into the carb A LOT better.
If you happen to have the same carb as I do, the carb has a fuel shut off built right into it in line with the hose fitting. so on mine, all i did was put the brass fitting into the tank in place of that silly pet-rooster, and i rely on the carb mounted shut off to do the job. Fuel flows like crazy with no restrictions for me, and when the shut off is closed, no fuel comes out, no drips, no slow leaks...it works great.
I do have an in line shut off valve for a lawnmower on my other bike, and it works great too.