240z Choke adjustment | The Z Club of Great Britain

240z Choke adjustment

Discussion in 'General discussion' started by Bobafett, Dec 27, 2017.

  1. Bobafett

    Bobafett Forum User

    Bit of advice or help please if I may ask.

    Have a 1973 240z which originally had flat tops but the previous owner installed earlier Hitachi carbs without all the emissions paraphernalia.

    Car runs great when warm no flat spots and pulls throughout the rev range. However, with cold start it really is pants. Barely catches, and everything serviceable was renewed as part of the recomissioning in the year.

    Is there a procedure to adjust choke setup?

    Have tried to search the archives, but nothing relevant or substance came up.

    Thanks in advance.
  2. smileyinside


    Hey Bobba!

    I had the same problem on my 260 with 240 carbs. Turned out to be mainly due to timing not being advanced enough. (Now set to 34 degrees at 3K RPM without Vac hose connected and plugged at the carb during setting process. Works out about 17 degrees at idle).

    I find it now starts a lot better without choke or very little at all.

    Have you also checked a couple of obvious things like carb balance, fuel delivery and compression?

    I'd personally start with timing+ ignition lead/spark plug/coil/ rotor arm / dizzy cap health first.

    Good luck and let us know how you get on.
  3. uk66fastback

    Z Club Member

    Is the choke actually working effectively? Have someone sat inside the car work the control while you look at both carbs - mine was shocking - gunked up to crazy and ineffective.
  4. johnymd

    johnymd Active Forum User

    From what I can remember, the choke has 2 stages. Check it operates fully and both carbs move together.
  5. dav118118

    Z Club Member

    I had a similar problem that turned out to be one jet was being pulled down further than the other causing rough running on the choke. However the biggest problem I found was getting the jets to seat correctly when the choke lever was pushed back in. I found that a t wouldn’t quite seat on one or both jets causing rough and unstable running at idle. Some micro fettling gets the jets to seat but it’s a bit of a faff esp if the choke cable has been kinked in the past. The mechanism needs quite a hard push to fully seat the jet. I’ve tried additional springs etc to try and encourage the jets to seat when the choke is pushed in but all this does is give resistance when applying the choke in the first place and you end up having to hold the choke in place when warming the engine through plus it makes for a stiff operation.

    I also greased up the choke cable to prevent any stickyness in the operation that will eventually cause you to crack the centre consel, which I have done!!

    I would do this first as it’s an easy fix, hopefully prior to delving into the carbs, esp where your carbs have beeen set up and and running fine when warm

  6. Bobafett

    Bobafett Forum User

    Thanks for the info chaps.

    Will have a proper look and hopefully diagnose what the issue is. Have done some initial research also, and wow - quite surprised how few moving parts there are in the SU/Hitachi carb. I have played with Webers and Holleys before, but will certainly have a go.

    There's not much I can see now for 'choke adjustment so apologies for the daft question. Hopefully it is something simple as a sticky linkage, but will strip and overhaul.

    Will also get rebuild kits from Mike Feeney before I start.

    Thanks again,
  7. Bobafett

    Bobafett Forum User

    Had a bit of a play today, and carried out a bit of a diagnosis.

    First issue I found was the choke lever not doing its job!!!...

  8. Bobafett

    Bobafett Forum User

    Then 2nd issue I found was choke tube' under carb is sticking. Tried cleaning but needs a strip own and I believe the 'centralising'


    Anyway, much better now with cleaning, - Z starts first time on choke :)

    Thanks for your help girls and boys!
  9. uk66fastback

    Z Club Member

    Vids unavailable ... :(
  10. Bobafett

    Bobafett Forum User

    Damn privacy settings on YouTube, now sorted - hopefully :)
  11. toopy

    Z Club Member

    Thats the jet, and yes its probably gummed up a bit, defo remove and drown in carb cleaner, the surface may need some very careful attention with very fine emery paper, but avoid that if possible.
    Also check the rubber hose, it needs to be supple and flexible to operate the choke properly, if its hardened and stiffened it needs replacing.
    I think its available still, but i used some suitably sized motorcycle fuel pipe which is more flexible than the standard car stuff.

    Its the needle attached to the piston that needs centralising in the jet orifice, but i cant remember if that applies to Hitachi's or proper SU's, might be both or neither!

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