Another with gas in air box
 

I haven't been on the bike in awhile. I had not left much gas in it so I decided to dump it a go fresh. I decided that while I was at it I would change out the fuel filter. Got a new one, changed it out and put things back together. Bike started right up and soon fell into a smooth idle. I let it sit for a few minutes, revved it a few times, no hiccups. Checked for any leaks and there were none. Shut it down and put it away for the day. A couple of hours later i was in the garage and noticed a gas smell. Found gas to be dripping from the front side of the engine. I pulled the tank and there were no visible signs of leaks from the tank. I opened the air box and found gas in the bottom of the box. I cleaned it out. There wasn't a huge amount in the box but I checked to make sure the filters were not wet. I gently blew through the two vent lines that go to the tank. They were unobstructed. When I blew through the smaller tube that goes to the back side of the petcock, gas came up from the rear carb. Any ideas as to what I need to check?
Mine you, the bike was running fine with no leaks last time I had it out. The only thing I did was dump the gas and change the internal filter. And, it started right up and ran smooth. It seems like the gas came back up through the rear carb after I shut it down. Would that be the diaphragm in the petcock?
Thanks for any ideas.

Could be both the petcock diaphragm and float valve failing. Look at the float valve first.

Agreed with the above post.
Check your oil level too to make sure it didn't get past the rings and into the case.