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Thread: Where does this tube go?

  1. #1
    Registered User steve91tt's Avatar
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    Default Where does this tube go?

    I am the proud new owner of a low miles, all original, no rust 1973 240z. I've been spending time under the hood getting familiar with everything and I found that the vacuum advance hose is not connected to anything. The vacuum advance works and holds vacuum nicely but I don't know where to stick the hose. I've looked in the FSM and spent my time searching old threads but I can't find a photo of where the advance tube is supposed to go. Anyone got one?

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    Registered User mayitin's Avatar
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    it goes behind the SU where the intake is.

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    Registered User steve91tt's Avatar
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    Quote Originally Posted by mayitin View Post
    it goes behind the SU where the intake is.
    Do you mean under the SU near the intake manifold?

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    DeesZ (John) DeesZ's Avatar
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    Default

    Post a picture so we can see what carbs you are referencing. Are they the flat-tops (as found on most 73 mods.) I assume so since you mention 'all original', or perhaps round-top replacements which are very common? Either way, there should be many pictures available among us.
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    Steve, I'm not sure if flat tops are the same as round tops, but on the round tops there is a small vacuum fitting that sticks up front the throttle body (actually on the carb itself and not on the intake manifold, next to the thick spacer/gasket that separates the carb from the intake mani). At the very least this should be plugged or capped since it will change the mixture if open to atmosphere.

    If you go on the ztherapy site you should see some diagrams or pictures of this. I believe it is also mentioned on the datsunzgarage site.

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    And we need pics of the 240, it's a rule you know.
    things will only bother you if you let them.

    82 280zxt 4 spd auto
    73 240z--lsd, cv axles
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  7. #7
    Registered User steve91tt's Avatar
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    Quote Originally Posted by DeesZ View Post
    Post a picture so we can see what carbs you are referencing. Are they the flat-tops (as found on most 73 mods.) I assume so since you mention 'all original', or perhaps round-top replacements which are very common? Either way, there should be many pictures available among us.
    I have the flat tops at this point but a set of round tops are on the way from ztherapy.

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    Registered User steve91tt's Avatar
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    Quote Originally Posted by tlorber View Post
    Steve, I'm not sure if flat tops are the same as round tops, but on the round tops there is a small vacuum fitting that sticks up front the throttle body (actually on the carb itself and not on the intake manifold, next to the thick spacer/gasket that separates the carb from the intake mani). At the very least this should be plugged or capped since it will change the mixture if open to atmosphere.

    If you go on the ztherapy site you should see some diagrams or pictures of this. I believe it is also mentioned on the datsunzgarage site.
    I don't see any empty, plugged or otherwise capped vacuum ports near the carb spacer.

    I did not find the carb diagram for the flat tops on the ztherapy web site.

  9. #9
    Former frequent poster sblake01's Avatar
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    Quote Originally Posted by steve91tt View Post
    I did not find the carb diagram for the flat tops on the ztherapy web site.
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    Default Pictures

    There are pictures that can be found in our photos gallery that may help. I did a search on "flat top" and came up with this:http://www.classiczcars.com/photopos...?searchid=4460
    You may find more trolling around there as well.
    Search function here is invaluable! (Just be aware that not all results are flat top carbs....)
    Last edited by DeesZ; 01-16-2010 at 11:35 AM.
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    The stock manifold on my 73 has two vacuum ports on the carb mounting flange, as well as another that appears to have been blocked off with a screw, perhaps when the PO converted to round tops. I'm not sure where the vacuum advance for the flat tops went originally but it may have been there. When I got the car the vacuum advance hose was attached to a T coming off of a vacuum port on front carb. This can be seen in the pics below. I haven't measured the vacuum on this port but plan to based on the info in the balance tube section of this page: http://datsunzgarage.com/engine/

    The first pic shows the vacuum hose routing as I received the car from the PO with round tops. The blue line show the hose from the diaphram on the dizzy, the yellow arrow indicates where this hooks into a T attached to a vacuum port on the round top carb body, the green arrow shows where the throttle opener control and anti-backfire valve vacuum attachments are, and the red shows the location of another possible vacuum port blocked off with a machine screw. There is an identical screw on the rear manifold. The second pic is the emission component layout for a 73 from the FSM. The 3rd pic is the stock layout on an unmollested 73 with flat tops. Sadly, you can't really see the destination of the advance hose but it looks to go to the same area. This is the best pic I have of a bone stock 73 engine.
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    Last edited by =Enigma=; 01-16-2010 at 08:53 PM.
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    Quote Originally Posted by =Enigma= View Post
    The stock manifold on my 73 has two vacuum ports on the carb mounting flange, as well as another that appears to have been blocked off with a screw, perhaps when the PO converted to round tops. I'm not sure where the vacuum advance for the flat tops went originally but it may have been there. When I got the car the vacuum advance hose was attached to a T coming off of a vacuum port on front carb. This can be seen in the pics below. I haven't measured the vacuum on this port but plan to based on the info in the balance tube section of this page: http://datsunzgarage.com/engine/

    The first pic shows the vacuum hose routing as I received the car from the PO with round tops. The blue line show the hose from the diaphram on the dizzy, the yellow arrow indicates where this hooks into a T attached to a vacuum port on the round top carb body, the green arrow shows where the throttle opener control and anti-backfire valve vacuum attachments are, and the red shows the location of another possible vacuum port blocked off with a machine screw. There is an identical screw on the rear manifold. The second pic is the emission component layout for a 73 from the FSM. The 3rd pic is the stock layout on an unmollested 73 with flat tops. Sadly, you can't really see the destination of the advance hose but it looks to go to the same area. This is the best pic I have of a bone stock 73 engine.
    This is perfect! Thank you for all your effort.

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    Default

    Sorry to revive an old thread, but it occurs to me that this port is before the throttle butterfly valve. My vac advance isn't doing anything at idle, and there is no vacuum signal from the port on the carb body.

    I would think to get a proper vacuum signal you need to have the port after the butterfly. can someone shed some light on this?

  14. #14
    Boat Anchor Repairman Captain Obvious's Avatar
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    If there's no vacuum advance at idle, it's operating exactly as designed. It's known as a "ported" vacuum signal and it's supposed to peak right off idle at light cruise pedal position.

    Here's some discussion and theory about such things:
    http://www.classiczcars.com/forums/e...ld-source.html

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