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choke adjustments on SU carbs

940 Views 8 Replies 5 Participants Last post by  ianz
i just ordered the SU book and will be tuning the carbs this weekend. i dont think they are off much except for the choke, but want to get a good baseline on them to make sure.

the car runs a good now, but on morning startups (around 50 degrees outside) the choke has to of course be pulled, but it runs really rough and some black smoke belches which is obviously rich. i know the choke richens up everything, but should it run rough like that with choke on anyway or should it be smooth running with choke on as it warms up? just trying to get the choke situation cleared up before the temps drop into the 30-40's.

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Is the rpm's coming up also when the chokes are opened? The butterfly should be slightly cracked open when the chokes are pulled. There is an adustment you can make by bending the little arm on the side of the carbs to judge how open the carb becomes. It is best to do this with the carbs off the car and then you can measure it. The Hayne's manual gives a good reference on how to adjust them.

yes the rpm's come up when the choke is on.
It maybe too rich and it's loading up the plugs?

Don't open the choke as far?
yes, i hit the choke halfway to fire it up then back it way down just to keep it running for a minute.

its definatly very rich, but when its off the carbs are fine.
Remove the domes and set nominal nozzle depth at .100" If you don't have dial calipers, screw nozzles all the way up and then back down to 2.5 turns.

Bend the "fast idle" linkage so that throttle opening starts at the same time the nozzles begin to drop:

Remove the choke cables, and operate the choke levers by hand. Place one finger on the nozzle down under, and pull the lever with your other hand. When you feel downward movement of the nozzle, watch the throttle butterfly for motion. The throttle butterfly should begin to open just when the nozzle drops. If this isn't the case, bend the link connecting the choke to the throttle until it's right.

None of the SUs I ever adjusted came properly set from the factory.

Also lubricate the fuel nozzles with graphite or copper type grease to prevent sticking, which is the main problem with these carbs.

The proper fast idle will prevent overly rich burble and plug fouling. (i.e. more choke.......more fast idle)
ok thanks,

these were Z Therapy carbs purchased about 6 months ago so i assume the owner before me checked them out adjustments wise but i hate to assume ya know.
AH HA!!!

Z therapy carbs which means you probably have SM needles which run rich as sin with the choke on......

it's the price of SM needles.....but the benefits are worth it......
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