Yep, it's really important to turn your fuel off. The old style petcocks on the right (points) side of the tank also have a problem in that the rubber seal can be fine, but if the sealing washers under the two mounting screws are stuffed, fuel will leak past the screws, into the bowl, and into your carbs.
It's not hard to overwhelm your float needles, especially if they're the old style all metal ones without the rubber tips, and if your seats have any crap on them, fuel will run by. The big problem you've got now, is did any of the fuel run into your engine? If it did and there was an open valve it will have run into that cylinder, past your piston rings and into your sump.
Pull the oil dipstick and smell the oil. If it smells like gas, or if the "oil level" has risen considerably, you've got a gut full of gas and you need to dump it all out and do an oil and filter change. And make sure you turn your fuel off! Cheers, Terry.
