Cb500 98 twin no fuel flow

[Castro12]

I have the above bike but cant get it started, the plugs are dry so i unscrewed the carb bowls drain screw and noticed there's no fuel in them. I then removed the vacuum hose from the petcock to the left carb and sucked on the vacuum hose fuel on the left carb immediately began to pour out of the left drain screw hole but hardly anything on the other side. The bike has in an line glass sight type fuel filter which is about half full, I should add that the carbs have recently been rebuilt so no chance of the floats sticking and I've gently tapped the bowls with a rubber mallet to see if I could dislodge anything if they were stuck. But why is the fuel no running freely into the second carb??

[Tinkicker]

Because it is on its sidestand and is leaning to the left?

[Castro12]

No! It's on its center stand