John, I'm no expert at anything LBC (just see my previous posts), but I
thought you were supposed to fill the carb dampers with a lightweight oil; like
a 20W or even Marvel Mystery oil. To fill them with "regular engine oil" when
you are running a 20W50 might bee too thick; no? Please enlighten me.
Jeff
'73 TR6
Subject: SU carbs
Author: "jonmac" <jonmac@ndirect.co.uk> at SMTP
Date: 4/14/98 8:16 PM
Hi, Justin
>Food for thought. Make sure your butterflies can close tight!
>Otherwise... you'll probably never be able to get a normal idle.
The SU has got to be arguably the simplest carb yet designed this
side of the pond, with the possible exception of the Wick Carb designed by
George Lanchester.
>From what I've been reading on SU threads over the last few weeks, it still
seems that some people are getting in a hopeless tangle tuning them.
Plenty's been written on how to go about it and checking the butterfly
closes fully is the very first step in preparing to retune. If it doesn't
shut completely, its the throttle stop screw holding it partially open (as
you mentioned) or the butterfly spindle has worn. I've come across very few
cases of the latter, though no doubt there have been exceptions of which I
remain ignorant.
At the risk of being repetitive, the starting point for setting up an SU is
a simple six fold check
1.Ensure the fuel needle is not bent. If it is, don't try to straighten it.
Get a new one
2. When re-fitting the needle, the base of the shoulder must be parallel
with the bottom of the chamfered hole in the piston, NOT parallel with the
bottom of the piston.
3. Ensure the sliding clamp pin operating into the yoke on the throttle
spindle is entirely clear of the of the yoke.
4. Ensure the butterfly is fully closed by unscrewing the adjusting screw
so it no longer bears on the spindle
5. Ensure the jet is exactly parallel with the jet bridge
6. The piston damper is filled with normal engine oil and falls with a soft
metallic 'clok' when lifted.
That's the set-up. Initial procedures prior to fine tuning for mixture and
idle speed are:
7. Turn down the jet adjusting nut by 8 flats
8. Screw down the idle screw by one point five turns to open the butterfly.
Each carb has to be adjusted individually for mixture with the other one
totally shut off. Ain't no way you can do two at the same time. When
mixture is the same for both, air intake is regulated using a
Unidoodlywotsit - or, a piece of rubber pipe. Alternatively, you can do it
"in stereo" with an old stethoscope.
It's only AFTER all this other work has been done, that the interconnector
pins are put back into the throttle yokes and tightened. People who fail to
do this and think they can adjust their carbs with two locked yokes will
NEVER get it right.
John Macartney
Now in the same museum as the cars he sold when they were new
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