Carb Flooding | The Z Club of Great Britain

Carb Flooding

Discussion in 'S30 (240Z,260Z,280Z) Engine' started by Rob Gaskin, Aug 28, 2017.

  1. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member

    I had a rare 'breakdown' on the way to the Gold Cup yesterday.

    Car began misbehaving and wouldn't tick-over. Then when I smelled fuel I decided to investigate because of the fire risk. I had an extinguisher in the car and also I'd decided to avoid the motorway thank goodness.

    Well I soon realised that the needle valve on the rear carb was the problem but 'tapping' the float chamber didn't cure it. Fuel was dripping onto my enlarged heat shield.

    Annoyingly on my carbs the cover on the float chamber won't lift off without moving the float chamber sideways. That meant I had to remove the carb to get at the 10mm nut that is hidden behind the linkage to the main-jet. I didn't know about that nut until yesterday.

    Undid the air-filter and about a pint of fuel poured out!

    So the reason for the post is to highlight the difference between the 3 screw and 4 screw dashpot designs and how to remove the float chamber cover. Mine is the earlier 3 screw carbs. Also carry an extinguisher just in case of fire.

    I cleaned the needle (it's not one piece but two and a tiny spring) and then it was sorted.

    Attached Files:

  2. uk66fastback

    Z Club Member

    And all this by the roadside - very impressed!

    Why do these things suddenly fail to work properly like this? I have the 3-screw as well.

    That's a great shelf-cum-heatshield as well!
  3. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member

    Yes why? I went out in the car on Friday to check all was ok. Adjusted tyre pressures including spare, checked oil, water, tools including jack etc etc. All was fine!

    Dave Jarman is responsible for the heatshield.
  4. jonbills

    Z Club Member

    Triple Dellortos is the only sensible resolution.
  5. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member


    I do have a plan for the winter and I have the hardware.

    Simple stuff like this is not the fault of one type of carb though. I need better filtration and more use. :thumbs:
    Last edited by a moderator: Aug 28, 2017
  6. franky

    franky Active Forum User

    You should carry your backup plan with you! Roadside swap over!?
  7. Mr.F


    4-screw dashpot is the earlier design. Most UK cars had 3-screw version.
  8. SacCyclone

    Z Club Member

    Hi Rob,

    Really sorry that you had that problem but it is not all that uncommon, especially on cars that have been sitting for years....I know yours does not.

    I have worked on over 20 early zeds that have been sitting for periods and the sticky needle and seat gives me fits. I have to say that with some fiddling, I have always been able to remove the float lid on both three screw and four screw type SU's. Yes, the four screw is much tighter space wise to get the float lid off but I have managed. Turning the float lid about a 1/4 turn and a slight angle before lifting usually does the trick. Of course, careful not to damage the float and mount tabs. Just wanted to throw that out there to save a bunch of time in carb removal. My mechanic showed me this trick several years ago after I said what a poor design it was.

    Thanks for the heads up on the 10mm nut that secures the float bowl.
  9. johnymd

    johnymd Active Forum User

    I struggled to fix this same issue on my SU's with the silver car. Lost count on how many times I removed the float lids. As Mike says, it is possible to remove it as he described but takes a bit of fiddling then you have to be careful not to damage the float.

    As an alternative to Jon's suggestion of triple, I'll suggest the much safer option of fuel injection :)
  10. franky

    franky Active Forum User

  11. datsfun

    Z Club Member


    Like for like, the Initial outlay and set up costs must be the double on EFI set ups compared to carbs ?
  12. nospark

    nospark New Forum User

    My rear su carb was flooding guite often. I took off the fuel rail and after rodding it with lecky cable I had
    compressed air blown through it. This has fixed the problem. I added a small in line filter between the rail and the carb as insurance as mine are not hitachis with the small internal fuel filter. Likely that fuel rails corode internally
  13. franky

    franky Active Forum User

    Plus on going costs o high heals.

    Yes, it's got to be 3-4 k with mapping and ecu or more?
  14. racer

    racer Active Forum User

  15. johnymd

    johnymd Active Forum User

    That's not a bad price (£2900 with an inlet manifold). A set of triples with manifold and linkage is around £2100. Not sure how much a pair of new SU's are but I'm sure a lot cheaper plus no on-going cost of high heals :)
  16. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member

    Can you buy new SUs? I contacted Burlen a while ago and they just aren't interested in supplying carbs for our cars.

    Have a look here - Datsun or Nissan aren't event listed:
  17. jonbills

    Z Club Member

    Looks like Burlen don't want to sell anything to anyone - everything I looked at is 'temporarily out of stock'
    Last edited by a moderator: Aug 29, 2017
  18. Farmer42

    Z Club Member

    I think you can get a pair of HS6 carbs from Burlen. They always say stuff is out of stock because they manufacture to order. Having said that, there will be a lot of fettling to do on the HS6 as the throttle linkage is different and I am not sure they bolt straight onto a nissan balance tube.

    The best bet is to go to Z Therapy in the States. They do the proper job and are not too expensive (at least until the shipping costs are added):(. Still cheaper than Webers & Injection kits. They also do full rebuild kits.

    Ali (Smileyinside) has used ZTherapy so he may be able to give some perspective.
  19. MaximG

    Z Club Member

    I was as wondering if it's down to the fuel having Ethanol in it that causes the problem. I seem to remember the tip of the needle valve is rubber / rubber coated. The Ethanol could be degrading it as it seems to attack everything else.

    Mike B
  20. Rob Gaskin

    Rob Gaskin Membership Secretary Staff Member

    If only you could order a new set of 1.75" or 2" SUs with linkages for a Z.

    My carbs are fine by the way so I'm not looking for any but if a really good pair of 2" came on the market I'd be interested. My engine is a modified 2.8 like my old track car and 2" SUs work well on those.

    Anyway I have a set of new Weber DCOE40s, Mangoletsi manifold and Nismo fuel rail ready to go on over the winter, however I'll keep my original carbs and manifold in case I can't get them working how I'd like. I need it to work well over the full rev range that's why I've gone for 40s. I'm a bit apprehensive because it's venturing into the unknown and so many cars I've seen with triples seem to have issues - not least horrendous fuel consumption. My car (apart from when it flooded!) is good on fuel and my old track car was too.

    I just feel I need to join the triple brigade to see if a performance advantage can be gained on my DJR modified engine, the previous owner was against triples.

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