Hi James
well, we all have our own theories and opinions........... and different ways of expressing basically the same things.
Simon's listing of base jetting, as established by Keith Nairn, is bang on.
Brett is bang on about the need to get float height exactly correct, and fresh fuel in the tank.
Ignition timing and advance has to be perfect to get best result.
Valve clearances have to be very good and no vacuum leaks from the intake rubbers, and no leakage from the choke plungers, which absolutely have to have the rubber tips in good condition and the choke plunger height set properly to be sure of a good seal when the choke is off.
so, usually I check and set valve clearances, then dial in ignition timing
for each ignition pickup, then put in place whatever air filtration is going to be used, make sure there are no vacuum leaks and that the choke plungers are seating, then do an initial carb synchronization with vacuum gauges. All of that will give you a solid base line to work from. Another thought, if you did not rebuild the carbs yourself, take out all three idle mixture adjuster screws, and fish out of their orifices whatever is left behind. Each mixture screw should have a rubber O ring seal, then a flat washer, then a spring, working from the tip back up the shaft. The rubber O ring has to be present, not perished, in good condition, and at the tip of the mixture screw. Also does not hurt to smear a bit of grease on the Or ring for even better seal. If the O ring is missing, you will never get your idle right due to the resulting air leak right through the mixture screw.
then, turn all three idle mixture adjuster screws all the way In, clockwise, until they seat on bottom, gently. Then turn each one out three half turns each, which is another way of saying a total of one and one half turns. If you have to, use the common mechanical idle adjuster on the cross bar of the carb rack to raise the idle so the engine continues to run, then individually turn each mixture adjuster screw in about half a turn, and out about half a turn with the engine running, and observe what happens to the idle.
having typed all that, my best guess is you are going to wind up around 60, maybe 58, 65 will likely be way stinky rich, 55 will likely result in a hard to start and slow to warm up engine that is hard to get to stay idling, but to a considerable extent the result will depend on state of tune, general condition of the engine, and even the altitude above sea level as well as the use of an air box or individual filters. My experience has been that a Laverda 120 ill comparatively run poorly with individual filters and will idle so much better(and in fact simply rum much better overall) with the stock air box back in place. No harm in cutting two round holes in the bottom of the 120 air box the same size as the ones in the front of the air box for the intake manifolds, in fact you can add extra rubber manifolds to the new bottom holes.....
my two cents.....
Paul LeClair
