Dave-
As you tighten the mixture nuts, make sure the jet itself follows
the backside of the nut-
The springs which return the jets to their normal position after the choke
has been used sometimes become weak and do not pull the jets snugly up
against the backside of the mixture nuts, resulting in a rich mix. As a
test, pull the choke On and observe the way the jets move ( seen just
below the mix. nuts.) Push the choke off, and with your finger, press the
jet upward, to see if there is any additional movement. If so, you may be
able to resolve this with stronger springs ( or just clip a few turns out of
the existing ones...) or if it moves but feels really gummy then there is
probably no other choice than to renew the jet seals. I think there are some
'better than new' materials for this, which allow for an easy choke pull
and reliable return to the warmed-up position. ( also make sure the sealing
surfaces on the jets are really clean and smooth, for best operation of the
chokes..)
The needles and jets might be worn, although this usually only
happens when the needles and jets are not centered and rubbing occurs. This
usually makes the car run terribly, and you mentioned that the carb pistons
move freely already ( although, rubbed until clearance develops???) and is
just too rich. My money is on sticky jets.
Good Luck
Bob Westerdale
59 3A TS 36967E
-----Original Message-----
From: willgray@region.net [mailto:willgray@region.net]
Sent: Monday, July 17, 2000 11:11 AM
To: triumphs@autox.team.net
Subject: SU Carb Tuning
I suspect all you experts on this list are going to roll your eyes at this
enquiry, but as a newcomer to this business of being my own mechanic
(although I did own and drive a TR 2 way back in 1959/60.Wives and family
have filled the intervening space), I am currently attempting to what
laughably seems to be called "tune" the SUs on my recently acquired 1957 TR
3A (of uncertain historyand a bit worn round the edges, although she goes
and stops reasonably well, and seems to have mostly original parts).
Following the instructions in a variety of manuals including Hynes and
"Practical Hiints for the Maintenance of the TR 3", I balanced the air flow
as best I could using a length of tubing, then with the engine idling at
about 700rpm, I lifted the piston of one of the carbs the requisite 1/16
inch, at which point the revs increased slowly, supposedly indicating the
mixture is too rich : I turned the adjustment nut one flat up (leaner?) and
found to my suprise that the nut was virtually at the end (fully closed) of
it's travel.
Does this mean that the jet/needle is so worn that there is fuel flowing
even when the throttle is closed? Both carbs seem to be the same. This
attempt at tuning was prompted in large part by finding the plugs with a
black deposit after a longish outing. The engine has been "reconditioned"
and uses virually no oil, and the exhaust is clear. I had diagnosed too
rich a mixture.
Dave.
TR 3A 1957
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