BS38 Throttle Cutaway

[xsbean]

Hey everyone, I’m running over the carbs on my 79 special. I’ve got everything up to spec, but I am interested in how to determine my throttle cutaway. I know what cutaway is but in my manual, the spec for my cutaway is listed as #120. Can anyone tell me what this means?? cheers!

 

[xsbean]

Also noticed the butterflies say 120, maybe that’s what it means?

 

[5twins]

Yes, it's the number of the butterfly plate. I'm not exactly sure what it denotes, maybe a measurement of some sort. The early BS38s ('70-'73) use a different one, a #125. The later BS34 carbs also have a different one, a #135.

 

[xsbean]

Thanks 5twins. Got any good suggestions for good pod filters that don’t block air intake holes? The original airboxes didn’t come with my bike, I can’t find any anywhere.

 

[5twins]

UNI foam pods are the usual choice. For your BS38s, you'll want the UP4200 or UP4200ST (dual layer). These have a 2" I.D. inlet and fit the BS38s like a glove.

 

[Jim]

the spec for my cutaway is listed as #120. Can anyone tell me what this means?? cheers!

@TwoManyXS1Bs measured the angled edge of the butterflies and found a correlation between the edge angle and the number. Your #120 plates have an edge angle of 12°. A 125 plate is 12.5°
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