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Thread: Lemons Race car....carb questions

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    Default Lemons Race car....carb questions

    Hi all-

    We recently picked up a 74 260z with an L28, carbuerated, for racing in Lemons. We had to put in a new fuel pump, fix a stuck float on rear carb (round tops), new NGK plugs, and put in a battery. Here is our problem:

    Car runs awesome for awhile. then it develops a flat spot that it wont accelerate. IF we let the car sit and idle for a few minutes, it will run well again. Any ideas? Car is a BLAST to drive and we are really excited. We are thinking perhaps no fuel vent return line is the culprit. Any ideas would be great. Thanks!!

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    Rust Free'ish zKars's Avatar
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    fuel pressure. Many causes. Line getting plugged, fuel pump failing. is your gas tank vent working? Put a pressure gauge on it after the pump and watch it while driving
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
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    Nova Scotia,Canada,Earth Blue's Avatar
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    Fuel delivery is the 99% cause but some times the distributor causes this symptom too.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



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    Thanks. We have new filters before and after the new pump. We did use a MR Gasket universal electric pump. Our first thought is to put a regulator on it. What pressure should the SUs be getting? Thanks for the help guys!

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    Probably not the pump but more of an obstruction issue. What's the history on the tank?
    Also a possibility of heat effecting ignition somehow?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Quote Originally Posted by madkaw View Post
    Probably not the pump but more of an obstruction issue. What's the history on the tank?
    Also a possibility of heat effecting ignition somehow?
    Tank unknown. The car ran last year with the previous owner. It has been sitting. We drained and filled with fresh gas. I suppose thatsa possibility with ignition. We thought we would try to get the fuel pressure correct and then start looking at other things. I have read that these carbs can get vapor locked if they don't have a fuel return line connected? Great idea with the fuel pressure gauge in line to make sure it is staying consistent. We will keep you posted and thanks!!

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    If you can drive around with the hood open and place a clear fuel filter where you can see it, you can easily see fuel starvation...I know from experience.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


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    Pull your sending unit and look at it and take a peek into your tank for rust .
    Sounding "flat" sounds like not enough fuel.
    Also check your float bowl hoses. Old ones will collapse when hot and pinch off fuel
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Thanks all. were going to drain and pull tanks this weekend. quick question, would capping off the vent lines at the tank potentially cause this? PO capped them off.perhaps no air can get in to replace fuel being pulled out?

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    OMG, yes, that could have an effect. No pressure equalization, pump starts sucking the tank flat..... things go downhill quickly.

    There is supposed to be a small vent in the gas cap, make sure it's not plugged. Early caps didn't have it, 74 though sure should. If your cap has a flat bar to grab, it should have a vent.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

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    Quote Originally Posted by jrtester View Post
    Thanks all. were going to drain and pull tanks this weekend. quick question, would capping off the vent lines at the tank potentially cause this? PO capped them off.perhaps no air can get in to replace fuel being pulled out?
    So that's why I can't fill my lawn mower with my gas can when the little cap is on in the back. I thought the little cap was for my weed eater fillin
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    There is a picture on the net of the reverse,,,, blow-through turbo setup where the boost collapsed the sealed brass floats.
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


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    Sweet (:roll eyes

    We will keep you guys posted!!

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    So we dropped the tank and filter and found this!! thanks for the input and help!!
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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