Any visible wear ion the needles is bad news. They are turned to
.0001 precision and wear at the idle end is particularly bad. Also take a close
look at your nozzles. A little wear goes a long way, expecially at idle.
I was looking at needles for the 2000 to replace the stock N-17. You
might try the British SU needle MC. Its just a little richer through the
midrange and some more richer at WOT.
The needle selection thing is a real art. I would highly reccomend the
book "How to build & power tune SU carburettors" by Des Hammill. It is
available through Amazon or some of the other on-line book dealers. It is the
best
I've seen on setting up the SU carbs.
keith williams
> Hi all!
>
> I am having some troubles getting my SUs working
> properly and not sure how much of it is due to having
> the "B" cam in it. Some on the list have given me
> some great help (thanks DatsunMike for the awesome
> spreadsheet!) and I am making headway.
>
> Is anyone running a 2000 with SUs and the "B" cam?
>
> ENGINE SETUP:
> - 68 2000
> - de-smogged since 1976
> - Rebuilt SU Carbs, new floats but old needles
> - Air/Fuel nuts 1 turn out on front carb, 1/2 turn out
> on back carb
> - No visible signs of blowby at the throttle shafts
> - About 2000 miles on a total engine rebuild
> - recurved distributer about 30K ago
> - MSD 6AL
> - Exhaust is 2" with (2) 24" glass packs in series
> - new "B" cam about 30K ago
> - Old needles are 1.53" long (short?), have no
> markings and show wear at the idle and off idle
> position
> - The diameters of my needles match closely to a KK
> for the first inch but lean out (larger diameters)
> compared to the KK for the last half inch.
> - The length of my needles seem to be shorter than
> most of those I have seen in the spreadsheets
>
> SYMPTOMS
> - running a little rich at idle - smelly
> - lean off idle and part throttle - stumbles
> - pulls hard to 4500 then starts to taper off above
> that (lean? rich? I hear no pinging, no high temps)
> - setting the carbs richer makes for stronger low end
> power up to 4500 but not much difference at full
> throttle above that
> - setting the carbs richer makes it hard to synhronize
> them, requiring me to screw in the idle screws and the
> back carb is already all the way in to begin with.
> - Tried some longer needles in from an old 240 (richer
> at idle - leaner at the high end) which made it run
> smoother without stumbles at the low end but flatter
> at the high end
>
> What do you all think?
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