SU Float Chambers

[Paul N-M]

All nicely done Terrytuned.
I ran an HS4 on a semi downdraft Y manifold on my second special which worked very well. Usual engine mods for the time, Jack French type of thing, and a tubular exhaust. Went very well indeed. Could keep up with a 3ltr Bentley on country roads. Never found carb too big but of course its all down to the engine spec.

Paul N-M

[Rogerfrench]

I think the main issue wit h an SU that's too big isn't so much the choke size. After all, being a constant depression carb, if you don't have enough suck the piston won't fully rise, so it's a little self-adjusting. What you lose, of course, is the full range of the needle that you get in a carb that's the right size.

[Mark R]

Looking at the semi updraft use of an HS2 or similar I'm thinking this may be best for my setup as the float chamber etc is where the exhaust manifold is. How can the fuel level be properly modified. When using an HS2 from 30 to 0 degree standard setup there is no adjstment for float chamber height Vs the jet is it just a compromise or am I missing something. Terry or others do you know how much the drop down needs to be for 30 degree semi updraft use of an HS2 please?

[Terrytuned]

You need to drop the float chamber 3/4" to give the correct fuel level for semi updraught, you also need to lengthen the the jet feed pipe. Photos show mounting for float chamber there two types of float camber on an HS2 you need to flatten the faces. Cut the nylon jet tube short insert the brass liner from the float camber end so the rubber fuel pipe can be clipped use a small length of copper brake pipe(3/16") and use the nut, washer and rubber ring on it to fit in float chamber end pre bend the copper tube to align pipe to jet
Terry.

[Mark R]

Thank you, that's very helpful, saves me starting from scratch working it out.