By ear?? Yeah, right! :)
With modern portable tachs and/or a
Colortune to assist, why rely on old technology when the modern stuff will do
it much better/faster and more accurately.
The Colortune is a godsend and needs no
explanation.....'cause it comes with a written one! Know what to look for
according to the directions and following
them will get you there most efficiently
when setting mixture. It's a great tool.
12 flats "out" or "down" from the jet bridge
is a sensible nominal starting point, Dan
and you should follow the tuning procedure
indicated in your Haynes, Bentley or Chilton
manual. Additionally, if you've got the rods...
...those rods came in the SU kit along with the jet adjustment wrench, jet
centering
tool AND a complete set of written directions on tuning single and multiple SU
carbs.
When the mixture is correct by Colortune, then it's correct by color of
combustion.
With the portable tach, you are looking
for a momentary increase of no more than
50 rpm when the air valve is lifted 1/8", before the engine settles back down
to essentially the initial idling speed you had
before lifting the air valve to check for
mixture strength.
Just bend down and
line up your eyes with the intakes and insert the flat of a small screwdriver.
Lift
the air valve a tiny amount while you watch the portable tach for that
"momentary" increase in rpm when mixture is correct.
When you "change" mixture strength on one carb, you must check again BOTH for
mixture strength, considering they are interdependent. You'll end up going "back
and forth" a couple of times but eventually
you'll get it right.
Even, or "synchronized" air flow is a good
part of accurate setting and I would highly
recommend a Unisyn (sometimes called
a Unisynch) or Carbalancer to visually
set equal (idle) airflow, rather than the "subjective" listening thru a length
of
rubber hose to get this right!!
I have tried all three and personally prefer the Unisyn (www.LBCarCo.com or one
of the other usual suspects).
Before setting mixture strength, follow the
procedure outlined in the manual for dis-
connecting all appropriate linkages. When
you get good at this and know what to look for, you won't have to necessarily
do this with a set of well-functioning carbs
except for throttle linkage loosening re: idle airflow synch. as it changes
in accordance with engine compression/
leakdown over time (engine "wear"),
but for starters, follow the procedures outlined "in the book" exactly.
Once you get mixture strength accurately
set, the difference between correct setting
for summer vs winter operation should be
about between 1/2 and a full flat considering the difference in engine
compartment induction air temps when operating in 90F summer temps vs 32F
winter temps.
Once you take the time to teach yourself to do the procedure by the book, it
all falls into place and becomes second nature in time. The Colortune and/or
portable tach
(linear, not digital) takes all the guesswork
out of it, providing a set of well-functioning
(no "sticking" air valves, fr'instance) carbs to begin with.
CaptBob
'60 :{)
Cap'n. Bob '60 :{)
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