Stuart
Nothing to do with your question, but I spotted the following in the
late Don Jackson's booklet "Your SU Companion" about 1 1/2 in carbs on
the 1250cc TF engine:
<<In May 1953 the prototype 'T.F.' was delivered to S.U. for them to
check the carburation. First it was tested thoroughly, as it was, and
then the results analysed. S.U. soon found that it was over-carburated
- that is, the H.4s were too big for the potential of the engine. With
the H.4s, it was found that, at full throttle at 70 mph, the piston lift
was only half an inch - less than half of what it should be, and this
despite the fact that lighter than usual piston springs had been
fitted. This made needle selection virtually impossible and to get
reasonable fuel consumption, power at the lower speeds would have been
sacrificed. At this stage, they fitted the more normal H.2s and ran the
tests again. These gave much the same maximum power output, and
eliminated the 'flat' spot at the lower speeds. Piston lift at 70mph was
3/4". Specific fuel consumption figures given below, show how much more
efficient the H.2s were :-
Road speed under full load Specific fuel consumption
(pints/BHP/Hour)
mph H4s H2s
10 .85 .82
20 .78 .69
30 .75 .70
40 .76 .63
50 .75 .70
60 .82 .72
70 .88 .84
You may wonder why the T.F.' finally went into production with H.4
carbs. It was said that M.G. felt that the selling point of "larger
carburetters" for their new model was too important to dismiss, so they
had to stay.
If you want to get better results from your T.F.', therefore, fit a pair
of "T.D.' carbs and EU needles!>>
Don was a test engineer at SU in the 50s.
I have no idea whether this is also relevant to TD Mark 2 - I just pass
it on without comment.
Regards
Cliff
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