Since this went to print I have an update, first in case you didn't know the SU HIF38 is a 1 1/2" and the HIF44 is a 1 3/4" carb. The HIF38 uses a 90 thou jet and the HIF44 uses a 100 thou, the 38 uses an A-- needle and the 44 uses a B-- needle spring loaded. Complicated. The Stromberg CD150 uses a 100 thou jet which got me thinking.
I have since changed the jet in my HIF38 to a HIF44 100 thou with a BDL needle and it works very well with pulling power up to 60 [ speed limit ], I haven't used it enough for economy but the plugs are a good colour. I have also made a new sandwich throttle bracket.