N27 needle equivalent?

[Boomguy]

Has anybody found an equivalent match to the  n27 needle in an SU needle? The n27 needle does not show up in in the SU reference charts. There must be someone who has plotted the 12 or so zones of this needle in the 45 years it has been around. Any help will be greatly appreciated.

C

Ps. I think I put this originally in the wrong area so I apologize for doubling up here.

[Chickenman]

N27 doesn't show up in SU charts because the Datsun carbs are not SU's. They are a copy of the SU design. However, as you mention... someone somewhere has to have measured them. Ironically, I did just that back in the late 70's when I was making some custom needles for my 240Z race car. And i just mailed my last set of N27's today to a fellow in Hong Kong. Could have miced them for you if I saw this post a day ago... Sorry. 

[Chickenman]

Double irony.  I live in Coquitlam.... Sorry again. 

[Boomguy]

Hey Chickenman thanks for the reply. You would think somewhere on the Web someone would have posted a comparison between these Hitachi needles abd the Su equivalent.... can't find it. I took my car over to my friends shop and we did some testing with an Innovate Lm1 air/fuel system and laid down some numbers. Thought I had sm needles in her but turned out they were N27 when I double checked, now to figure out the zones with a micrometer and what spacing to use for each zone and how many readings. 

[Diseazd]

Bruce or Steve at Ztherapy should be able to direct you to where you can get that info.

[240260280]

I think Captain Obvious characterized some needles on this site.

FYI Now that I have a lathe, I am catching up on ideas I have pooled.  I am am currently building a needle fabrication machine for making customized needles.

I may offer customized needles eventually.

[240260280]

http://www.classiczcars.com/topic/51593-measurements-for-stock-su-jet-needles/

[Stanley]

Maybe the problem with using the British SU needles is that they're bigger (leaner) at stations 1 & 2  (0.099" vs. 0.095). My car, stock 240 displacement with some mods, was going lean at top end WOT with N-27's, stock and modified, so I put SM's. That fixed the top end miss, but to get it to run at low rpm under load I had to lower the mix nuts about a half turn from where they were with the N-27's. This causes it to run too rich at lower mid-range swhich is usual for around town. Every few weeks I need to un-foul the plugs.

It might be OK just polishing down stations 1 & 2 on the SM's. That should allow the mix nuts to be raised to get better A/F ratio at low end and better gas mileage around town. It would lean out the top end though, so the WOT miss might come back. Another idea would be to push the SM's a little further up in the piston, so station 2 becomes station 1. Haven't heard of anyone doing this, though.  

Maybe unmodified SM's would work correctly on built 280's with SUs. It would seem to make sense since they'd need more gas at low end too. Anyway, there are a bunch of British needles available and they can all be modified, so there should be something that will be perfect for any size and tuning stage of engine and for every driving style. Stock N-27's should be right for a stock (including stock air cleaner and exhaust system) 240z.

I had planned to do a 3-D graph of all the applicable British needles in some unknown way that would be useful to myself and others, but it's a huge amount of work and I'm busy, so it might not ever get done. Maybe someday...

[Captain Obvious]

13 hours ago, 240260280 said:

I think Captain Obvious characterized some needles on this site.

Guilty as charged.

I'm not aware of an equivalent match for the N-27's and I believe that profile was developed custom for Hitachi for the Z's.

Many people run the SM needles, and Stanley well described the issue that some people find with them.

Boomguy, Just sent you PM as well.

[SteveJ]

Could this be of any help? http://www.teglerizer.com/suneedledb/090needlesortjava2.htm

[Chickenman]

On my modded 1971 240Z ( Cam M445 Shadbolt, 2.5" exhaust, ported and polished E31 head ) I ran E88 needles if my memory is correct. . Again those were perfect at the Top end but too rich at idle and low range with the Cam and Mods I had.

So what I did is install the needles dropped .020" from the flush setting. This leaned the low end , but kept the Top end. Taper changes fairly rapidly at fat end, but the taper is slow at thin end. I just used a set of Vernier calipers set to .020" and butted the needles's shoulder up against that. Then tightened the set-screw. Mixture came out perfect. 

[Boomguy]

Chickenman were those the N38 needles that you used from the 280z? I am finding the N27 too rich at idle and low end.