I've actually found brake-kleen (the stuff in the green can) works well for blasting out the wee little passages. Depending on the type of carb, you might be able to get away with just taking the carbs off, (the whole rack off), taking your float bowls off, examining your gaskets, and *one at a time* unscrewing the jets etc, cleaning everything out with the brake-kleen (won't harm rubber in the long run, might make it swell a little temporarily) and checking to fiche that all your stuff is *there* (I've noticed that on a lot of these older bikes, we, as 2nd, 3rd or so owners inherit a long list of jerry-rigged chickenwire fixes...) blast out the little passages, learn which passages go to which little jet within the carb, make sure your accel. pumps are working, if you have them) (take the top (bottom?) off 2 and blast through those little passages until you get a small jet through all four) etc etc. I've never soaked my carbs, for fear of what the stuff would do to any rubber I may have accidentally left in place. That, and I'd recommend the minimalist approach first, then more and more involved as you see fit. If your carbs are leaking, it may be due to your float height, or stuck floats in general... sometimes you can give the carb a good knock with a rubber hammer or the handle of a long screw driver for a quick fix.