SU carb question....SM needles, 5.5 turns down.....wow

[A to Z]

SU question.

I was running N54 needles. WAY too lean, I got them to 4.5 turns down (at 6000+ elevation) and they finally stopped popping and ran until I hit 4000 RPM then that was it. When I went to change the needles, the needles were allt eh way in. So, I ordered some SM needles and went at it again. I set them with a straight edge level with piston bottom. I had to keep turning down I'm at around 5.5 or so turns down and the popping stopped, but driving I can smell the gas, and it is still acting like a governor ont he engine. The engine is definitely being held back. The engine is a 2859CC with 11.5 to 1 compression, ported head E31, with larger exhaust vavles, again ported out, nissan A cam exhaust manifold with free flow exhaust.......the engine isn't that hot, why are my SU's having such a devil of a time with it? Do I really need to sand/polish the needles at WOT? instead of 4000 RPM, its now 5000 RPM. I will reset the timing, but at this altitude we don't have air, so why would it need SO MUCH FUEL? thanks.

[madkaw]

I went thru this recently on a customers car . Similar L28 with a Maxima head but with a Bonk cam -520 lift . 
This car was an automatic which really made it a challenge . After playing with float levels I ended up about 4.5 turns with SM needles . Maybe you are pulling air from somewhere else ? I ran an electric pump if that makes a difference . 

[Miles]

If the SU carb has an air leak, it will create a lean condition for which no amount of tuning will correct.

 

The problem with the SU carburetors is that the throttle shaft becomes worn and allows air to seep past the shaft and into the carb causing a lean condition.

 

You can try contacting ZTherapy who specializes in  SU carbs and parts.  Also they sell a video called "Just SUs" it explains how to repair and tune the SU carb.

 

Just SUs video covers:  4 hrs of advanced college level theory of operation, diagnostics, tuning, surgical Weber removing and disposal.  Covers all years of Japanese Hitachi "SU" and 1.6L-2.0 Volvo HS6 1 3/4" SU (HS4, HS2 same).  Our newest video, 4 years in the making.  Directly replaces the first 1.5 hrs of ZTV01. Heavily updates and corrects info from ZTV01.  Part one is inspecting and  installing new ZT carbs and "Tuning for Dummies".
Part two is "Installing and Tuning a ZT Master Tuneup Kit for Dummies".  Balance of tape is answering common questions, racer tech and mods, airflow studies, horns, cold air box, etc. We address the Q+A sessions from the 2000 MSA and LSV shows-I worked hard to answer your questions on this video. If this does not answer every issue you ever had about the mighty SU, call me!  If you still don't get a satisfactory answer, demand your money back!!!  Ships free with new ZT carbs and the ZT MasterTuneUp kits.   Available in single play mode on two 2 hr SP tapes for $20 or on one single EP mode tape for  $15 (lower video quality). DVD available for $25

 

https://www.ztherapy.com/

 

 

 

[A to Z]

UPDATE.  Seat of the pants tuning, and trial and error.....2.25 turns down, 20 degrees timing at idle with vacuum plugged at 6400 ft. elevation.  runs pretty good!