I am having trouble getting my S/U l28 to Idle. No matter where the idle adj screws are set the idle eventually falls to 400-500 before shutting down. These are newly rebuilt carbs (minus new throttle shafts). I am so tierd of fooling around w these S/U's. I wish I would have just gone EFI.

Are your plugs black? An overly rich condition can do this

We need some background info. What negative symptoms caused the rebuild. Who rebuilt them and were the linkages, throttle shafts, float bowls totally taken apart? What source are you using as a reference guide for tuning and what have you tried to get it running correctly? The float setting is the primary mixture adjustment.

3 hours ago, Patcon said:

Are your plugs black? An overly rich condition can do this

Yes. Not heavy build up but definitely black. Ill start over with the mixture settings. 

1 hour ago, Mark Maras said:

We need some background info. What negative symptoms caused the rebuild. Who rebuilt them and were the linkages, throttle shafts, float bowls totally taken apart? What source are you using as a reference guide for tuning and what have you tried to get it running correctly? The float setting is the primary mixture adjustment.

I got this car in a bunch of pieces. I rebuilt them because I didn't know their condition. I used a Ztherapy kit. Everything was cleaned and adjusted to Ztherepy recommendations except for the throttle shaft bushings.I am using a mix of Ztherapies grainy video, https://zcarguide.com/tuning-adjusting-datsun-240z-su-carburetors/, and https://www.z-car.com/blog/cars/tuning-su-carburetors. I spent a lot of time dealing with the floats I think they are correct. 

It's been a long while since I've read this but it seems like the fuel pressure was a main link in the switch over. Maybe the fuel tank vents too? Anyway here's the thread from an old friend I've bookmarked for my "one day soon" SU swap over on my '77. 

 

Edited August 11, 20206 yr by siteunseen

3 hours ago, Civilizedape said:

Yes. Not heavy build up but definitely black. Ill start over with the mixture settings. 

 and a new set of spark plugs.

Any luck so far @Civilizedape?  I'm having similar issues with my build, so I'm interested to hear how yours turned out.

6 hours ago, rcv said:

Any luck so far @Civilizedape?  I'm having similar issues with my build, so I'm interested to hear how yours turned out.

It turned out to be a fuel issue. The fuel pump was cutting out after start up. I had the safety oil pressure switch wired wrong.