Great writeup and following info.
The only experience I have with hif carbs was years ago when I put an mg metro engine in a minvan. The 38 that ws supplied with the engine was woefully underpowered. After fitting the correct 44 the transformation was night and day.
Since then I have stuck to hs carbs and a suitably needled hs4 will easily power a HC 1275. It is what I am using now.
I did find that with a hs4 the dissy curve is extremely important as well as the correct needle.

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Cheers Dave.