jonmac wrote:
>
> 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
John, not disputing what you say, but every thing that I have read and
every carb shop that I've talked to say the neddle must be flush with the
bottom of the piston.
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