Righty Tighty, Lefty Loosy! (the Navy taught me that
in Machinist Mate "A" school about 22 years ago!)
But remember your looking down
on the carb, so its opposite. Tight means shutting off the
gas, loose means opening it up. (actually setting the initial
height of the needle in its bore, but the analogy is good).
Tune up points and plugs
and set valves before fooling with the carbs. If there
is a problem with just one carb, I would balance the linkage.
Basically make sure both carbs start opening at exactly the
same time. (you have to pop off the little plastic things
and make one of the rods longer or shorter to do this)
Also, adjust the idle speed with the screws on
the carb , not the master screw on the linkage. If everything
is balanced well, adjusting either idle speed screw will make
the engine slow down or speed up. Both screws should be adjusted
the same turns. You can very carefully observe when the screws
first touch the lever, and set both screws to this point, plus about
one turn, as a starting point.
Then, once balanced, make sure the floats
are the same height before you fool with the mixture adjustment.
I used some clear tubing from the hardware store
and wired them up next to the float bowls from their inlet
at the bottom of the float bowl.
People will
quote various heights as proper, but more important than
exact height is that both are exactly the same.
A little too rich is better than a little too lean, unless
your going to drive up a mountain, in which case it
will get too rich as you go higher. (We are talking about
at least a few thousand feet change, usually not
a problem).
Look at the tailpipe immediately after a good fast run,
it should be dark gray to black, any medium or light
gray means too lean. You can back this up with
a more accurate measurement by looking at the color
of the spark plugs, which will also indicate if
one carb is different than another.
I remember my neighbors
1970 Chevy Wagon, when smog controls were
first starting, but compression was still high.
He was worried about the almost white tailpipe,
and for good reason, his (and thousands of other)
350 four barrel V-8s burned exhaust valves
within 20,000 miles.
Funny, I was just starting High School at the time,
but I was completely fascinated by this revelation....
a foreteller of things to come in my life I guess.
Best Regards,
and hope this helps.
Jim
Chesapeake Va
----- Original Message -----
From: datsunmike
Sent: Saturday, June 08, 2002 11:16 PM
To: audela2; Roadster Mail Group
Subject: Re: Adjusting carbs question
Start from scratch and tighten both mixture nuts all the way closed
(counter-clockwise) and then back each out 1.5 turns to start out with.
Give the car a tuneup and check the timing to get it right.
Then make sure there's oil in the carbs - I use straight 20 wt. but others
may use something else. Then balance the carbs.
Burning too rich or too lean will cause overheating as well as a lot of
other things too. Dieseling can be caused by a variety of problems including
carbon build up and sharp edges in the combustion chamber.
Mike
----- Original Message -----
From: "audela2" <audela2@cox.net>
To: "Roadster Mail Group" <datsun-roadsters@autox.team.net>
Sent: Saturday, June 08, 2002 10:05 PM
Subject: Adjusting carbs question
> I'm really new to adjusting SU carbs, and I have a situation I need help
with.
> I get some backfiring from one of the carbs, and when the engine is shut
off
> it still runs a few seconds, then dies with a puff of white smoke from the
> carb. The engine runs very roughly and heats up quickly, and I've read
that
> this could be because of a rich fuel mix. Although all the guides talk
about
> adjusting the idle screw, I'm confused as to which direction makes the
fuel
> mix richer. Any insight would be greatly appreciated!
>
> Charlotte & Leonard Hoover
> '64 SPL310
> '67 SPL311
>
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