I am one of the many Z owners, with SUs, that has battled a lean condition on hard acceleration, or WOT.  My idle and cruise AFR readings (have AFM attached to header) are great at 14.5 or so, so have adjusted it as best as i could.  Along with SM needles, I adjusted fuel levels and tried to do anything I could think of to resolve this issue, to no avail.  I even switched to triple Webers, which allowed me to see how my car could really perform with appropriate AFR!  I decided to switch back to SUs, as I had some linkage sticking and fuel dripping that bugged me.  

So, I started looking into the different available SU needles to see if I could find something richer.  I looked at various charts and saw that the SB needle had the same configuration at the top two levels (so idle is the same), and was slightly richer heading down the needle.  I thought, let's give it a shot!  I could not find anyone locally that provides SB needles, so I went down under to Australia and ordered a set of SB needles from Competition Products for about $40 delivered (less than 2 weeks for delivery).

I was stunned at the improvement!  My idle and cruise AFR remained around 14.5, but my lean (16 to 17+ AFR) condition at WOT was gone, now hitting around 13.5 AFR!!  That is ideal!  I cannot believe the difference.  My L28 was rebuilt with flat top pistons years ago, but outside of that, there is nothing else outside of the norm.  

I would strongly recommend this solution to those with similar issues!  I strongly urge you to make sure your fuel level (and flow) is appropriate before you go this route, as that can resolve many of the lean issues.

Edited February 26, 20196 yr by duffman

I like stories with happy endings!

If you don't mind sharing, what was your source in Australia?

CP or Competition Products is the name on eBay, but the direct website is sumidel.com, they provided the SB needles for around $40 delivered to Arizona.

Edited February 26, 20196 yr by duffman

Great contribution to the Z community!

Are these the ones you ordered

NEEDLE (SB)

$12.50

Product Code: AUD1318

**Please choose your metering needle carefully as they are non-returnable. All sales are final**

 

Yes


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Link: http://www.sumidel.com/shop/item/needle-sb-

Thanks, Phil, I should have included the link!


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Good results!

So was there a thread here on the forum where you were working on fixing the WOT lean out problem with the SUs? I don't remember such a thread, but that sure doesn't mean it didn't happen.   

Yes


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I am going to give them a try. Have them on order


72 body and block, everything else 71, Tokico springs, Illumina, R180 CLSD, 83 close ratio, 3.90 gears, Ztherapy SUs, BRE 15X7 Libre wheels and BRE front spoiler.

No, CO, I did not create a thread about this in the past.  I read other threads about fuel levels, fuel pressure, etc.  I even learned how to rebuild SUs and bought old sets, rebuilt them and sold about 15 sets on eBay!  I learned a lot about how they worked, but I could never get my SUs to attain desired performance on my Z.  I guess after a while I just decided to live with it!  My triple Weber adventure taught me that I can get more from my Z than what I was able to get with SUs.  There had to be something I was missing, that other people were able to attain great results with SUs and there was no reason I could not either.  So, pursued a variable I thought would make a difference and solve my problem; needles that allow more fuel on acceleration or WOT!  

Edited February 27, 20196 yr by duffman

How many turns down for the mix nuts with the SB's?  I tried SM's for my modified 240z engine but found I had to drop the mix nuts a couple of extra turns to get it to idle, which made it way too rich at midrange, fouling the plugs. That's because the SM's (and other British needles that fit, as far as I know) are 0.099 at station 1, compared to 0.090 for the stock Hitachi needles, like N-27's. When I installed a modified 280/280zx engine, the first needles I tried were modified (richer at mid-range and top end) N-27's. Looks like my AFR numbers are about where the engine builder wants them so I guess I lucked out.

Checked my book, it shows SB's same as SM's at the top two stations, then they start to lean out more than SM's like you said. Anyway, your AFR numbers look OK, so however it works, it works. I've read where someone planned to drill out the nozzles to use British needles. Have also read about pushing the needles up into at piston as far as they'll go which is about 1/8" or 1 station higher than FSM says to put them. But that would only get you to 0.095 at the top station (if my 1/8" measurement guess is correct), not .090.