How do I know if I need to rebuild my Carbs?

In what condition would a carburetor have to be in so that the carbs need to be rebuilt. I am in the process of cleaning mine but don't know If i should really be rebuilding them. What conditions must be present? pics would be great!

 

Cleaning and rebuilding tend to overlap.

If the float bowl gaskets leak when the screws are tight - replace w/ new.
If the little "O" rings from the Pilot needles (go fish them out) appear flattened or in any way worn - replace.
If you had a surging, floating idle when warm/hot, get and do the (8) throttle shaft seals.
If the needle/seat just doesn't seal, causing high/flooded float levels - despite your efforts at polishing the seat - replace needle/seat

The more you replace, the more you are doing a rebuild, rather than a cleaning.

 

Think of it as a carb service. Plan on replacing most all of the o-rings and gaskets; but for the other things, like TIME said, you replace those as necessary. And "necessary" is determined by disassembly, cleaning and careful inspection.