Bonneville America Forums Forums Technical Forums General Tech Float, needle, and seat valve

Is there anything other than a failing float needle and seat valve that would cause gas to run out of the overflow hose and the back of the left carb?

A stuck/damaged float. It rides up and down on a hinge pin. If that pin is sticky or dislodged the float can be stuck in the down position allowing the fuel to keep flowing.
Sticky = need to run some cleaner thru - Seafoam.
Dislodged = you (or someone) recently had the bowls removed and didn't get things assembled correctly.
Damaged = somehow the float has a hole in it, is full of fuel, and no longer "floats", allowing the gas to run continuously.

It's also possible that the tab on the float is set too low and the float isn't shutting off the fuel soon enough when the bike is on the side stand...of course, this requires user intervention to occur, it doesn't just happen on its own (ask me how I know). This time of year in the northern hemisphere it wouldn't be uncommon to have a sticky float from fuel "varnish" after sitting up all winter and a dash of Seafoam should cure the problem.