Anyone have a diagnosis for the way my bike behaves on idle. When I come off the throttle the idle sinks to about 500 rpm (just barely running and always about to die) and then after a second increases to a very steady and reliable 900 rpm -- which is where I would like it to always be. The bike is a 1964 650SS with twin new (6 yr old) Monoblocs. I am not running air cleaners and my intake manifold is about an 1/8 longer than stock because I have doubled up the heat insulators. My slides are 3 1/2 per the standard set up and seem to be in very good shape (they are the chromed version). I am running my needles on the top notch because any lower and the bike sputters accelerating up from idle. The bike now picks up cleanly and runs nicely from idle on up. The bike seems to like Champion N4's better than NGKs and ignition is by magneto. Do I just have a set of worn slides? The carbs have only have about 2,000 miles on them -- but then again I am not running an air cleaner. I could, I suppose, put in a set of nos slides and see what happens. Any ideas? Domitwin.

I'm going to answer my own question. The cause of the problem, and of a general rich running condition, was a leaky float. First time I've ever heard of the plastic floats on Monoblocs leaking -- I thought leaks were a soldered float specialty. Always learning, always something new.

I used to have a concentric float that was 1/2 full of gas for show. Rare failure, but should be looked at when the motor is running rich. Orlin inSC/USA