Fuel evaporation? | The Z Club of Great Britain
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Fuel evaporation?

Discussion in '240Z / 260Z / 280Z' started by Sam_C, Mar 3, 2017.

  1. Sam_C

    Z Club Member

    When my car (240z, standard carbs) is warm, it starts straight up. I found that if I left it for a week or so, int takes a lot of turning over to get it started. Once started, no problems. I wondered if the fuel was evaporating/leaking somehow, so I left it for standing for a couple of weeks. Then I took off the fuel feed to the rear carb . I would have expected a bit of residual fuel, but nothing came out at all. So I removed the carb, took the top off the float chamber and found that empty too.

    I appreciate that the float chamber is vented to the air filter backplate and therefore it's not a sealed container as such, and if the fuel actually can evaporate then it makes sense that the fuel in the feed pipe is going to go the same way when the float drops, opening the needle valve and letting the fuel from the pipe run into the float chamber.

    Question is....is this fuel loss to be expected, and if so is there any way to prevent it, aside from fitting an electric fuel pump? (which I don't really want to do)

  2. Mr Ex Jnr

    Mr Ex Jnr Zeds is the way iv been shown Staff Member

    mine takes a bit of starting aswell but there no choke on mine help start it, you have to manual pump throttle can take few minutes to start mine up from cold.

    if I come to it next day start all need to do is fearer throttle turn key fire up

    leave it few weeks as I don't use it a lot and ill have repeat the process but mine on webbers aswell take a bit of feeding lol
  3. SeanDezart

    Z Club Member
    Official Trader

    Yoiur fuel won't be evaporating.....but you maybe getting an airleak and therefore the pump starts turning on air. 260Zs came with a small electric pump at the rear to get it along to the mechanical pump at the front....maybe that is your best path - nothing fancy.
  4. uk66fastback

    Z Club Member

    Twas always the problem with carbs really ... my old 'stang could take AN AGE to start. Maybe five mins ... prodding on the throttle for ever and then hoping to catch it - the car having stood for a fortnight or so.

    The Z is much the same. From warm no problem(again, to be expected). Anyone found a discreet place for an electric fuel pump yet? Could you have an inline one INSIDE the car? Maybe not safe though (or even legal) - I have no idea!
  5. Sam_C

    Z Club Member

    I did suspect some kind of air leak at first Sean, and that still might be part of the problem. . However...it wouldn't explain the total lack of fuel in the float chamber. The fuel can't go back up into the feed pipe, it can't go up into the carb as even with a full float chamber the "U-bend" effect (e.g. balancing out the height of the fuel in the chamber and the carb fuel nozzle) would put the fuel no higher than the jet bridge. So it's either evaporating or...??? Only other thing I could think of was if the fuel line was pressurised enough (and it would have to be air) to push the fuel out and up into the carb. But that seems a bit fanciful!

    Maybe splitting the fuel feed pipe just before the mechanical pump, mount a (hidden of course) electric pump somewhere at the front and re-joining the fuel feed line somewhere after the mechanical pump?
  6. jonbills

    ZClub Administrator
    Staff Member Moderator

    If your car has stood for a week or two, it's not bad idea to crank it for 10 seconds or more before firing anyway, just to make sure you've got oil upto the head.
    Fwiw, here's how my electric pump is mounted: levelish and below the level of the tank.
  7. Farmer42

    Z Club Member

    Even with an electric and a mechanical fuel pump, it still takes a few turns for my car to fire up after sitting for a few days. I normally let the electric pump run for a few seconds to build fuel pressure going forward before turning it over.

    The other thing is to check that your choke is working properly. When the lever is pulled it sometimes feels that it has activated it whereas in fact the cable stiffens up and the linkage on the carb hasn't moved. If it feels stiff, try lubricating the cables within the outer sheath so that the lever travels right back when pulled.

    All this won't affect whether the float chamber is empty which it shouldnt be even when sat for a while. You might want to check that your float valve is working properly to allow fuel in. Otherwise you might want to check for leaks in the feeder pipe between the float chamber and jets. I found a small hole in mine which allowed the fuel to drain out but the fuel pump was creating enough pressure to fill the chamber whilst running so I thought everything was ok.
  8. richiep

    Z Club Member

    There is a mounting location near the tank on all Zs (including early ones that didn't come fitted with an electric fuel pump) - near where Jon's photo shows his pump. There are captive nuts in the structural crossmember in front of the spare wheel well. These are there for a pump to hang in a protective shroud. That's where the Facet Red Top on my car is mounted, inside a small shield that my Dad made off a card design I gave him; basically a three-sided box that keeps the muck off the pump, which is mounted inside. It was a homemade equivalent of what factory pumps on later cars were mounted in.
  9. Rob Gaskin

    Rob Gaskin Treasurer Staff Member Moderator

    Check the valves in your mechanical pump, I've had one that gave problems when initially filling the carbs but ok when running.

    Perhaps you are expecting too much from the old girl?
  10. SeanDezart

    Z Club Member
    Official Trader

    Electric fuel pump ALWAYS at the rear and don't forget an inline filter BEFORE it - it pushes not sucks !
  11. Sam_C

    Z Club Member

    Any idea how much fuel the pump should actually shift Rob? Could do a test then to see if it is up to the task.

    I don't think expecting my Z to start easily after been stood for a fortnight is too outrageous to be fair! My 43 year old VW camper generally bursts into life first turn of the key after a month of inactivity no problem. Vorsprung Durch Technik, as we say in Hutton Buscel

    What is your standard car like Rob, does that have the same characteristics as mine?
  12. woody

    Z Club Member

    Maybe a non return valve may help
  13. toopy

    Z Club Member

    My fuel pump is mounted in the engine bay, roughly where the original fuel filter would be, the mechanical pump has been blanked off

    After weeks of standing in between runs, and months over the winter, she normally starts within 10 seconds on full choke with a light touch of the throttle

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