akpasta did you ever get this issue resolved. I have the same issue and I havent been able to correct it.
I can't find a repo or NOS petcock for my 65 scrambler 305 anywhere. Any help would be a Christmas gift to me.Why all the fun with 50+ year old parts? When it comes to fuel, a leak can be dangerous. NEW petcocks are available and not expensive. "Reproductions" $15-$20, new Genuine Honda $60.
Do yourself a favor and buy a new assembly. Don't fool around with fuel related issues that can burn up your bike or burn down your garage/shop/house. Don't ask why I know about that, it's a sad story. HondaJohn