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Information in this section is comprised from various sources including the web, books, magazines, Fast Idles Cheat Sheets, friends and my own experiences. Before acting on
anything you might read here, bear in mind that I can't garantee the accuracy of the information and that I do not accept any responsibility for the consequences of using it.
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NEEDLES
- The '70-71 240 used "N27" needles and related nozzles.
- The '72 manual trans used N54, the '72 automatic used N58, both with
the same '72 nozzles.
- The 2000 Roadster used N17's which are reportedly good for racing
when used in the 240.
- SM needles from British SU's are supposed to be great. Impact Parts
carries them.
- the 260Z intake manifold is said to produce 10hp more than the 240
version. It's stamped N36.
Use 1970-'71 carb needles and nozzles on a set of 1970-'72 carbs. The
'73-74 carbs/needles are shabby for performance.
CONVERSION NOTES
On checking I realized that the last carb owner had installed '72 N58 needles. So I immediately ordered a new set of N27's and '70 nozzles from the dealer. By squinting, the N27 needles appear to taper faster than the N58's, so they should run better on the top end.
After installing them the engine now idles silently and predictably, acceleration is powerful and linear, and gas mileage went way up. So I think replacing both nozzles and needles with NEW ones is one of the most significant (and cheapest) improvements I've made to this engine.
For a brief while, I also tried a pair of N17s from the dealer. They are 3mm shorter than the stock 240s, and the taper near the tip is much larger (richer). On the road the midrange seems leaner, while near redline it still hauls. I plan on keeping them for racing.
- Buy new rubber bushings from the dealer to hold
the float bowls to the carbs, make sure they're snug and level. Keep the
stock fuel return rail and use an aftermarket electric fuel pump with
3-5 psi. Higher pressure can overpower the needle valves, lower causes
the bowls to run dry on heavy acceleration. Don't use an injection fuel
pump (30+psi, too high.)
- I had trouble finding an electric fuel pump that worked at
low pressures. But then I remembered that the early '80s Mazda RX-7 used
a 4-barrel carb and had a 7000 redline. Suspecting it might be perfect
for a Z, I read the shop manual specs which quoted 3.7- 4.7 psi.
Perfect! I got it for $15 from my junkyard, it's quiet and powerful.
Always mount an electric pump as close to the gas tank as you can. It's
better to "push" the gas rather than "pull".
- Stay away from the auto-store Purolator electric pumps. Excellent
reliability I'm told, but very noisy. I tried 2 but both had a powerful
ratcheting sound like a tiny jack-hammer. Purolator told me that was
"normal", so back they went to Advance Auto.
- remove the little copper mesh filters in the float bowl inlets.
These can restrict flow. I have a Purolator "clear" fuel filter
installed where the hose comes off the firewall. This is easy to inspect
and clean.
- Retain the water cooling through the intake manifold.
- Don't block off the PCV hoses. It's important that the crankcase be
vented to the intake so the motor stays clean. Using a little K&N
breather on the valve cover looks cool, but stinks the car up with
fumes.
- Don't disable or block off air or emissions hoses. It won't increase
power...it'll throw the engine out of tune.
- Also keep the flow-valve connections to the carbs, otherwise the car
may reek of gas.
- Courtesy Nissan in Texas
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