I recently purchased a '72 240z and am having issues with the carbs. I don't know a lot about SUs so I havn't done much with them yet. I am having several problems:

When starting, the rear one backfires a lot, but only for a little while and consistantly at about 1800rpm.

After warming up, it will idle at about 1100-1200rpm, but will jump to over 2000 after driving awhile, then go back down to normal after about 10 minutes. I have never encountered idling problems like this, but have never worked with SUs before

At low rpms, it boggs a little and doesn't run well. I cleaned them and put 10w30 fluid in them because I heard that the thicker fluid can help, but that has had little success. Perhaps they are just running lean?

These SUs are a lot more confusing than other carbs that I've worked with, so any suggestions or references will be greatly appreciated. Thanks!

sounds like the back SU is running lean and the Previous owner cranked up the idle screw to compensate for it.

reach under the rear carb and turn out the big knurled knob about 1/2 turn, to see how that feels. Also start checking all of your vaccum hoses for leaks and loose fittings. 10/30 is actually a little thick for the SU's but if you check the dipsticks on top, you'll barely see 2 small lines, keeping some 20 weight near the lower line will allow the SU's to react a little faster under acceleration.

turn down the idle screws as you increase the fuel on the bottom half. Get yourself a flowmeter from the local auto parts store.

Use the Search function here at the site. There has to be a couple hundred posts from the pros about ajustment.

Good luck,

Dave.

synchronizer and the JUST SUs video or DVD will prove essential to your solving these and any other carb issues.

Questions? Give a call or email......

Bruce Palmer

sales@ztherapy.com

503-587-9800