i assume your running pods?
i had a bad outerwear once, that if would run fine until it got to power, then it wouldnt let enough air flow through, and would shut a cylinder down. something stupid that took me a while to find.
basically the same setup as mine and i have 28pwks. if you go any bigger you will lose bottom end, and maybe gain a little at the very top of the range.
not worth it.
no, you dont need bigger carbs until you get a lot more mods.
honestly, look at a timing plate, and porting, they are the best bang for your buck in the power department.
as far as i know, they bearings OD are all pretty much the same, its the ID that changes depending on the diameter of the axle.
I have 4 bearings in mine as well.
that leads me to think you have a hole in the float.
i cannot see any reason why the motor would cause it to overflow. if it has that much pressure returning to the carbs, i would think it would try to push back by the slides, not into the bowl.