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Re: Can you fit "75" R90S Del'Orto Carbs on a "75" R60/6
Posted: Fri Nov 22, 2013 7:52 am
by sprints@pldi.net
I've spent quite alot of time swapping carbs, milling them down from top to bottom in stages of .1 at a pass, bandsawing, and learning of internal passages over the years. Unless you can buy a Mikuni that is already setup almost exactly for that specific motorcycle, go with the Delorto or the Bings. Mikunis offer literally 100's of needle, jets, nozzles, etc that will break your bank account and drive you nuts - they work well when correct but have too many variables to dial in. The Delorto's have less than 1/10 of the needles, nozzles, and jets to contend with and are very good carbs.
Pushing the choke lever doesn't flood the carb, it only opens an enricherer passage like the Delortos old and new. (choke lever are not like an accelerator pump).
Last point - bigger is almost never better with stock street bike carbs.
Re: Can you fit "75" R90S Del'Orto Carbs on a "75" R60/6
Posted: Fri Nov 22, 2013 4:34 pm
by Jean
"Last point" I agree, Sprints.
Yes, I know Mikuni makes a bunch of different sizes but as stated by sprints, the tuning possibilities are close to infinite, and I'd rather ride.
Re: Can you fit "75" R90S Del'Orto Carbs on a "75" R60/6
Posted: Sat Nov 23, 2013 12:03 am
by PITAPan
Jean wrote:"Last point" I agree, Sprints.
Yes, I know Mikuni makes a bunch of different sizes but as stated by sprints, the tuning possibilities are close to infinite, and I'd rather ride.
The possibilities might be very large but the ones that work are already known. Unless the motor is fairly modified, a working Mikuni can be bought off the shelf jetted for the application. For a modified motor you start w/ the stock jetting and then work with the Mikuni tuning manual and some instrumentation to walk it in.
Any carb sized for a 900CC motor will be problematic on a 600. The airflow is much lower and with the big venturi you get less air velocity and higher venturi pressure. Hard to draw fuel from the jets with that. Massive jetting rework required. Then you loose your lower end torque anyway. Not a great idea.
it is desirable to isolate the carb thermally from the head. Floating them between rubber bushings also reduces vibration which in turn affects how the floats work. It's nice to have minimal corrugations in the surface of the fuel in the bowl.