The petcock from a Yamaha Raptor works manually instead of by vacuum... This is the way petcocks have operated for nearly a century until some fool thought that a vacuum operation would be clever...
I'm glad you've found the problem,... but, bypassing it, ain't fixing it... with it bypassed, you will no longer have a reserve, and whatever ain't right in there, will still be wrong... and, the Raptor looks better, works better, and makes tank removal easier for future maintenance...
I know it's an irksome thought,.. but the $23.00 you wasted on the stock petcock repair is still wasted, whether you buy a Raptor or not...
I'd strongly recommend getting a Raptor,...
This is the Raptor part no. 5LP-24500-01-00
2003 Yamaha Raptor 660 YFM660R
http://www.ronayers.com/browseparts.cfm?SearchString=5LP-24500-01-00&adv=5&kw...
PS,.. people recommend that you shut off a manual petcock when you park, but I never have... and it's never been a problem for me in 30 years... I only shut off to pull the tank or do carb work...
... as it is,... you have know idea whether turning your broken petcock to run position when parked is doing anything anyway...