A friend of mine put some early TR-4 Stromberg 175 CD carbs on his TR-6 cause
he liked how much more adjustable they are than the later ones with extra
emissions stuff on them. They are a good bit simpiler too.
Well he eventually put them back on his 4 which he put back on the road, and
got new ball bearing SU's that he is very pleased with. I seem to remember
him having a good bit of trouble finding stromberg needles and not much at
all finding SU ones.
To this end I will quote what I read the other night in the TR-4 competition
preparation manual which tells how to adapt SU needles to Stombergs. (note
this is for TR-4's and I'm not sure how it will apply to other TR engines,
but I thought it might be useful.)
CARBURETORS
The S.U. and the new Stromberg carburetors are very similar in design,
except that the latter uses a more easily adjustable jet screw, and instead
of
a machine fit on the piston and dashpot, utilizes a diaphragm arrangement.
The diaphragm gives a more accurate air depression and raising of the piston
than the S.U., but some trouble will be experienced in procuring different
needle shapes. We will deal first with the needles.
The simplest method is to make up a small .006" shim tube that will
slip over the S.U. needle shank. As the difference in diameter between S.U.
and Stromberg needles is .013", there will only be .0005" difference, which
will not hinder the fitting to the Stromberg piston.
Wrap a small piece of .006" brass shim stock around the shank or fitted
end of an S.U. needle; remove the formed tube of shim stock, and cut it in
half down the length of the tube. Now fit the S.U. needle to the Stromberg
piston, and slide the half-tube of shim stock in next to the needle shank op-
posite the piston set screw. This will force the needle up tight on the shim
stock when the set screw is tightened, and center the smaller needle shank.
There is not a definite needle correlation between S.U. and Stromberg carbu-
retors, because of the more accurate lift of the latter's piston. But the
method
described will put you close to the correct mixture the first time without
making up special needles.
Make certain that the top bearing of the jet in the Stromberg carburetor
does not stand proud of the carburetor body. This can be adjusted with
small shim washers under the jet bearing head. Should you experience a
lack of fuel in the float chamber, increase the needle and seat size to .225"
diameter, the stock size being .175".
Other than thinning the throttle shafts and throttle butterflies, there
is
not much else that needs to be done in the carburetor area. If you have
thinned
out the throttle shafts, be certain that you solder the butterfly retaining
screws into position.
The following are S.U. needle recommendations for the various Triumph
racing camshafts:
Lean Standard Rich
'C' CAMSHAFT S.M. R.H. R.G.
'D' CAMSHAFT R.H. R.G. R.F.
'F' CAMSHAFT R.G. R.A. R R
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