Carb/ Gass Tank problem

I posted a few weeks about about buying my first motorcycle it is a 1979 KZ650C. the couple i bought it off said it had sat in the garage for a while and had old gass in the tank. i bought the bike and bought a battery for the bike and we added new gas 2 the already old.My roommate and i started the bike up and he said he drove it and got it up 2 60. I tryed to start the bike later that night and couldnt get it 2 start. The next day my roommate and i got the bike 2 only idle for a little while after i gave it any throttle it would die . we added engine/ carb cleaner (threw gas) and it started again for a little while. Later I couldent get it 2 start and i opened a screw at the bottem of a carb ( i was jsut getting to know my bike) and found a rust flake come out. I looked into the tank and saw rust and sludge type stuff. I ordered Por 15 a motorcycle tank repair kit Por15 I am going 2 recive the kit Wednesday and am goign to start working on the tank.
Do you think that was my problem? and if so will this fix the problem.

Thanks Keith

The old gas may not be your only problem , but it is probably the biggest one .

While you are waiting for the POR15 kit , find a good local automotive carb repair shop who has an ultrasonic cleaning tank and get the carbs cleaned. This is by far your best bet if you are not real familiar with working on carbs .