Has anyone else here tried using Mikunis on a B in place of the original SUs?
When the HS4s on my ' 70 B-GT got past the point of another sensible rebuild I investigated options for replacement. New SUs were available here in Canada, but very pricey. I've always disliked the sliding jet choke system, as it seems like a series of leaks waiting for the opportunity to spring to life. Single side-draft Webers are similarly expensive, and guys I know who have fitted them to road cars have had trouble with them in terms of driveability in town and massive consumption.
In the end I fitted a pair of Mikuni HSR 42 flat-slide carbs meant for bikes, and they have really brought the old girl to life. It's an easy conversion, and the carbs are light years ahead of the old SUs in just about every respect. They're available from many bike shops and can also be found quite reasonably priced on ebay from time to time.
Because they are intended for gravity feed in bike applications, you need to stick a fuel pressure regulator in the line to stop even the modest pressure of the MG pump from blowing the needles off their seats, and because of the slight incline on the MG intake the float levels need to be lowered slightly. Jetting is straight forward and bits are readily available quite cheaply.
MG purists may turn up their noses when they open my bonnet, but the Mikunis do wonders for both performance and reliability, and are cheaper than a new pair of Skinners Unions.
KH Canada