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Mikuni BS40 Carb settings - confusion no more!

Posted: Sat Jul 30, 2011 6:09 am
by RING_DING
Hi all,
Couple of quick questions for the BS40 experts:
1. Pilot screw adjustment: Suzuki shop manual states 1/4 turn out for Pilot Screw. Haynes says 3/4 turns. Which is correct?
2. Float Bowl Gasket: I am not sure that I have the gasket in the right way around in my pic below. The shop manual says to have the extra hole "opposite" the starter pipe. Not sure whether I have interpreted "opposite" correctly.
As always, your advice & counsel greatly appreciated!

Re: Mikuni BS40 Carb settings - some confusion - please help

Posted: Sat Jul 30, 2011 10:43 am
by tz375
That's not too hard to answer. Bikes with #47.5 pilot jets used 1/4 turn (L) and those with #45 (MAB) set the fuel screw at 3/4 turn out.

The gasket is not so obvious, but the hole aligns with a cutout in the float bowl.What exactly it is there for is not clear. The extra hole doesn't line up with the air drilling to the pilot jet for example, so why it's there is not clear, but it goes the other way round. That brass tube in teh upper right of your picture is the starter fuel feed and the whole should be the other side of the needle jet to that.

Re: Mikuni BS40 Carb settings - problem solved!

Posted: Sat Jul 30, 2011 2:49 pm
by RING_DING
Thanks TZ! Carbs are back on, and she is idling away nicely.