I'm trying to decide what needle to try next in my SU HS6 carbs on my
TR4A. Currently I'm running the "rich" needles (SW). According to
both the "seat of the pants" method, and an O2 sensor, I'm running a
somewhat lean starting at about 2500 under heavy acceleration, and very
lean above 3500 under any acceleration. Pulling the choke, which drops
the jets about 1/4" (two stations) smoothes out the missing, but
according to the O2 sensor it is still a little lean. Above 4000 or
so, even with the choke out, things lean out again.
Using SU Search, I'm thinking of trying something like an RR, RV or RH
needle. They are all about 2-3 stations richer above "low cruise",
which seems to correspond to what using the choke indicates. Any flaw
in that logic?
Alternatively, can anyone recommend a needle for an engine with
following:
Mild comp cam
K&N filters
1.5:1 roller rockers
87.5 mm pistons
C/R calculated to 9.25:1
Headers
(there is more done to the engine, but I think that is all that is
relevant to needle selection).
Lastly, does anyone know of a good source for SU needles on the US west
coast? I know that Joe Curto carries a large selection, but I'd like
to save a few days on each cycle (I'm guessing it will take more than
one try to get a good fit).
Ultimately, I might try tuning the needles myself, as outlined in
"Building and Power Tuning SU Carbs", but I want to get to a standard
needle that is a bit closer to correct first.
-Darrell
--
Darrell Walker
66 TR4A IRS CTC67956L
Vancouver, WA, USA
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