The hissing may be a tank vent issue. Remove the seat and look at the lower rear of the tank where it bolts to the frame. Above that bolt flange you'll see a hose barb coming from the tank. It should have a hose attached, running down towards the ground. Check for pinching or kinks, especially if you have an after market seat. Then leave the tank lid open and start the bike and see if you find joy. I suspect you will find no change. Tank vent issues usually result in an engine that won't run at all until some pressure is let off or it bleeds down on its own. There are air vents in the fuel filler cap. They may hiss when venting.
What have you done to get the cob webs out of the circuits in that carburetor?
“many a trip continues long after movement in time and space have ceased”- Steinbeck, [I]"Travels with Charlie"
[FONT="Century Gothic"][I]Sometimes your only available transportation is a leap of faith[/I] [/FONT]