Hello all
Now that I have enlarged the manifold to accept the HD8 carbs on my
140, I have a question as to which needles should be installed? The
manual states that the VR was used on the H8 sandcast, but the HD8
was never fitted in pairs to a 3.4 liter. The carbs currently have
UM, which were correct for a 3.8 liter when three were fitted. Has
anyone fitted two HD8 carbs to a 3.4 liter, and if so, which
needles did you use? I should also mention that the engine is an
8:1 CR with 150 PSI compression, and the cams have 267 deg of
duration and .384’’ of lift. TIA.
Joel–
ex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
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Joel;
Probably what you will have to do is measure the “stations” on the VR
needles of the H-8’s and find a corresponding set for the HD-8. This should
get you close… but, as with any jetting adjustments, without a Dyno and an
Exhaust Gas Analyzer, it’s going to be a lot of Trial and Error…
Measuring the “stations” of the needles requires a set of quality
calipers, with a “dial indicator” (digitals are really nice) and a “sharp”
set of jaws. The “stations” are simply 1/8" increments, starting at the
“shouldered boss” of the needle (a very fine point marker/Sharpie, etc. is
very helpful to identify “where” to measure)… Keep in mind, the larger the
diameter of the needle, the more “Lean” it is at that “station”.
The Haynes book on SU’s, Strombergs, & Webers has an appendix listing
(nearly?) all the Needles and the diameters of their stations.
Hope this helps.
Charles #677556.----- Original Message -----
From: “ex jag”
Hello all
Now that I have enlarged the manifold to accept the HD8 carbs on my
140, I have a question as to which needles should be installed? The
manual states that the VR was used on the H8 sandcast, but the HD8
was never fitted in pairs to a 3.4 liter. The carbs currently have
UM, which were correct for a 3.8 liter when three were fitted. Has
anyone fitted two HD8 carbs to a 3.4 liter, and if so, which
needles did you use? I should also mention that the engine is an
8:1 CR with 150 PSI compression, and the cams have 267 deg of
duration and .384’’ of lift. TIA.
Joelex jag, '66 E-type S1 4.2, '56 XK140dhc, '97 XJ-6
Denison, TX, United States
Joel,
Charles suggests using the VR as a start, as these were fitted to H8s on
3.4 litre cars.
If you buy a pair of UVRs, these have the same profile as the VR, but with
a 1/8" shank, so they will go straight into your HD8s.
However, if you find that these work out too rich, I would suggest you try
UOs.
Regards,
David Lonsdale
Classic Carburetters
Cirencester, UK
+44 (0) 7786 912011
In reply to a message from DavidNLonsdale@aol.com sent Sun 31 May 2009:
Hi Joel
David built me a lovely pair of carbs for my 3.4 XK150. When
setting up my car I needed to get it running well very
quickly as I was booked to attend a trackday. So I ended up
get Chris Window at Racinggreen cars to sort it. He ended up
fitting UH needles before he could get it to work right at
the top end. Chris couldn’t remember ever having fitted UH
needles to a 3.4 before, but that was what mine ended
needing. It certainly ended up running very nicely and was
very responsive at road speeds. With this combination I was
seeing just over 5000RPM in top (non overdrive) at the end
of the Lavant straight at Goodwood.
XK150s have a B type head, so that will probably be
different to your XK140.
Cheers
Ken–
Ken XK150 FHC S824252, see her on xkdata + X300 3.2 Sport
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