Mikuni BS40 Carb settings - confusion no more!

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RING_DING
To the on ramp
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Suzuki 2-Strokes: 1974 GT750 B-4 (JDM), 1975 GT750M
Location: North Carolina

Mikuni BS40 Carb settings - confusion no more!

Post 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!
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Last edited by RING_DING on Sat Jul 30, 2011 2:50 pm, edited 1 time in total.
1973 Suzuki GT750K with Sidecar - Bonneville 2020
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tz375
Moto GP
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Re: Mikuni BS40 Carb settings - some confusion - please help

Post 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.
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RING_DING
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Posts: 447
Joined: Thu Apr 21, 2011 5:32 am
Country: USA
Suzuki 2-Strokes: 1974 GT750 B-4 (JDM), 1975 GT750M
Location: North Carolina

Re: Mikuni BS40 Carb settings - problem solved!

Post by RING_DING »

Thanks TZ! Carbs are back on, and she is idling away nicely.
1973 Suzuki GT750K with Sidecar - Bonneville 2020
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