Can't be drilled throuh - there is a vacuum valve the other side of that plate which turns the tap on when the engine spins. The OP is still active here - I sent them a message to see if they would tell more of the story...

 

Unfortunately the petcock can have three problems:
rupture of the membrane. A new one is put in and solved
Fuel leak from the o-ring. The rivets are drilled, screwed and a new o-ring is put on and it is solved.
But there is no solution for the OFF, ON, RES positions to intercommunicate, or at least I have not been able to fix it.
It is not possible to drill and tap, since the pad of the body of the petcock is very thin.

Excuse my English, it is a Google translation that is surely quite ridiculous.

 

It's perfectly understandable, thankyou - Es ist völlig verständlich, danke

 

I had same problem with petcock on 88 Hurricane. I bought the rebuild kit on ebay, and it worked perfectly. I highly recommend using the rebuild kit, it even has instructions and a drill bit.

 

The '88 petcock (SC21) is completely different from the 93' onwards (SC31) - there's no kit available for the SC31.

 

Well it looked really easy, then I got a call from a Neurosurgeon, and he says I need neck surgery (I am 77). but it is a simple procedure (for him?) 2 days and you are out and back at it. So I had the 600 down to pulling the carbs and decided to finish next week. That was a month ago and a week in the hospital. Now I can not look down for more than a few minutes without OUCH although I can sometimes drink a cup of coffee with my right hand. My baby is sitting in the garage whispering fix me, but even replacing the petcock took an hour and lots and lots of ouch ouch ouch. Next those easy to get at carb boot screws, ouch

 

Cbr600 petcock is totally different than the cbr1000f…