Mixture screws ,up/in for rich,down/out for lean.

Are we talking SU's?

On HS su's, screwing the adjuster down will richen the mixture, up will lean it off.

Andrew

What Carb yes they are differant

for HS Carbs
http://www.sucarb.co.uk/TechnicalDetail.aspx?id=82

or for

HIF Carbs
http://www.sucarb.co.uk/TechnicalDetail.aspx?id=74

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looking at the diagrams i'd say hs.is one more common.i have a origanal 1275 ls set up single 1 1/2"

1275 LS's originally came with a 1 1/2" HS4, so I'm guessing that's what you've got.

HS su's are probably the most common in oz, as they came standard on all oz Mini's, but plenty of HIF's are floating around now too.

Easy to tell them apart, HS's have the float bowl hanging off the side, with the jet hanging out the bottom, HIF's have the float inside the bottom of the carb (hence their name "Horizontal Integral Float"),and nothing hanging off the sides (other than linkages etc.)

Andrew

Screwing the jet down/out takes it away from the needle, making the gap between the needle and jet larger - more fuel to flow past - richer
HS carbs have the float bowl externally, HIF is internal float

Or for HIF carbs, im pretty sure scewing the adjustment screw in makes it richer.