You asked some comments if someone made a carburetter conversion with a Stromberg 175CD. I made it last summer, for a friend, and here are the procedure and results:
Starting point: a 1980 1500 Spitfire with a single 150CD carb. which was extremely anemic on performance. I choose the cheapest route with a 1976 MGB carb. in good shape. It is an easy modification and you could return to original set-up in less than one hour.
An important item is to find an used Spit. 1300 manifold as 4 feeding tubes port fit perfectly with Spit head as they are same size. Spit 1500 manifold has those 4 outlets reduced in size, for venturi purpose, highly restrictive.
Work done on 1300 manifold with a rotary tool:
· Grinding asperities inside manifold to have a soft surface
· Enlarge inlet of manifold to match larger carb. size
· Polish inside of manifold as far I can reach with flapwheel starting grade 80 and after grade 120
Manifold is almost ready to fit carburetter. The next step is slightly more touchy as you need some precision here. Original carb. is hold in place by 2 studs. A larger carb. implies studs are not located at same place. You must locate on manifold flange in a cross-pattern a new location for studs and drill+tap holes to accept original studs; two original holes are useless.
You could retain original water choke but personally I converted carb. to mechanical choke.
The only difficulty was to find “THE” right needle for your Spit. I will retain all the extravaganza involved to find it. The Lotus Elan Stromberg Excel needle calculator was a plus…
At this moment the car is working a lot better than with original 150CD with a needle B1AP from a Volvo. This is fine compare to original set-up and giving good fuel consumption, but slightly on the week side mainly in altitude in Adirondacks mountains. I will correct that with a more rich needle B2BC from an XJ6.
Finally a free-flow air filter is a plus mainly for the looks
This year I fitted needle B2BC and now that car exhibits a true sporty behaviour! That's the way to go.