Listers:
Though I am pretty much a mechanical rookie compared to others on the list
(and therefore pretty much just "listen in" to the list instead of
contributing to the threads), I might be able to shed some light on the 175
carb and manifold discussion since my 72 Spitfire has exactly that; a single
175 CD-2 Stromberg water choke carb and new manifold on a rebuilt engine that
was revised from a 1296 to 1500 using a 1500 block and a new piston set with
the longer stroke. The PO did all this work and I just inherited this set up.
All emissions equipment had been removed , and lucky me, you don't have any
emisssions requirements for pre-1975 cars here in Oregon. So my Mk 4 has a
bigger engine, bigger carb, and no emissions equipment which makes the car
quicker than most. How much quicker, I have no idea, since I have no point of
reference from never having owned a Spitfire before. I called BPNW for a part
one day and the guy explained that putting a 175 (TR6) carb on a Spitfire was
not all that uncommon. He suggested it would probably idle rough at 1200 rpm
and burn rich, but add a fair amount of power. He was exactly right. Another
experienced mechanic of LBC's suggested I replace it with a 150 if I ever
wanted it to run right and that it was just too big a carb for the car.
Another long time Triumph owner suggested I not only close up the air by-pass
valve, but plug the holes inside. He promised it would bring the idle right
down to spec (800 rpm) and smooth it out as well. I rebuilt the carb and
followed this advice and , sure enough, it worked like a charm. Still burns a
little rich, but all in all not too bad. Can't tell you which size bore I
have on the manifold since I have never had it off. Can tell you that the
carb mounts require 4 bolts, but I don't see any indication that anything was
welded on or adapted to allow this. Since I am just in a learning as you go
mode( and having lots of fun doing it with the help of the list) I just can't
compare this manifold to a "regular" Spitfire manifold since I have never
laid eyes on one. I thought I had a regular manifold until I started reading
this thread. If anyone is interested in trying this kind of carb setup, I
think I can report it seems to work pretty well. Maybe I'll take here out
tomorrow and see the time it takes to go 0-60 and let you know how much more
power this arrangement is producing. Again, I'm new to this and you will want
to check with the pros on the list to get your best information about the
merits of this carb approach.
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