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Thread: runs really bad on freeway

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    Default runs really bad on freeway

    so ive got another wierd problem with this 72 240z of mine. when i get going abut 60 mph it soundslike a lawnmower and boggs down till i get to maybe 45 miles an hour. But it cruises just fine at about 50-55. oh and it does this up hills too. i can take hills only about 25 mph. all of my emmisions crap is removed. ive replaced my fuel pump and filter, flushed my lines and cleaned the parts on the tank that the fuel comes out of with a clothes hanger and compressed air. pulled my carbs apart and cleanedthem out. steve at z therapy set my float bowls for me. and i replaced my points and checked my timing.. still does it... anyone have any idea what i should try next? someone suggested that i need a new distributor and that pertronix kit would fix this. But its pretty out of my budget right now unless i have to. well any advice would be appreciated oh by the way it idles good and drives just fine in the city.

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    Formerly known as Koalia Reverend's Avatar
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    There is multiple choices for electronic dizzys. Mine is unique, as it is made by my friend. Cost 60bucks. Pertronix is good but not the only option. If you have done all that work, it does sound like distributor related. Maybe the vacuum advance is bad..?
    -72 240Z "Goldie"

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    Registered User 5thhorsemann's Avatar
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    That it where I would go next, also. Clean lube and inspect all of the vacuum advance hardware, sounds like it works, just not properly. As for which electronic ignition, do a search, that dead horse has been beaten to a pulp.

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    Registered User Zforce's Avatar
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    Have you checked the the last chance filters in the carbs ? Su's run best slightly rich, also the stock fuel filter is a restriction. Another thing to check for is kinks in the rubber portions of the fuel lines and dents in the metal portions. Fuel system problems are often mistaken for ignition problems, no fuel of course there will be no ignition Doh!
    1971 240Z hls30-17121 L28/E-31 SU's "B" 4-speed 3:70 gears.

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    Registered User beermanpete's Avatar
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    I agree with Zforce. It sound like fuel starvation to me. New anything does not mean it can't be bad out of the box or suffer infant mortality. Check fuel flow rate and pressure. It sounds like your car is stock so the factory service manual specs and procedure apply. I attached the fuel system section in case you don't already have it. Perform the diagnostic procedures for the fuel pump. Also, check the screens at the inlet to the carbs as Zforce said, they are not included in the fuel pump diagnostic procedure.

    EF Engine Fuel System.pdf

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    Registered User LeonV's Avatar
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    Definitely sounds like fuel starvation, I would follow Pete's advice. Also, I want to second Zforce in that you need to check the pre-bowl carb filters as well and clean them if necessary.
    2/74 260Z

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    Registered User 5thhorsemann's Avatar
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    Why would it even out after 50MPH if it's starved for fuel at 45MPH?

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    Registered User Walter Moore's Avatar
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    Quote Originally Posted by 5thhorsemann View Post
    Why would it even out after 50MPH if it's starved for fuel at 45MPH?
    You didn't read it quite right. He says when he tries to go 60+ the car chokes and dies slowing to about 45 before it catches again. The 50 mph is max speed without dying out.

    That is the classic sign of fuel starvation. If you are still running a mechanical pump, check that the lobe on the crank pulley is tight, and that you have the pump installed with the correct spacers.

    Since the pump is new, my bet is a pinched hose or as someone else said the "last chance" filters in the float bowls.
    '71 240Z, Because any fool can drive fast in a straight line.

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    Registered User LeonV's Avatar
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    Quote Originally Posted by 5thhorsemann View Post
    Why would it even out after 50MPH if it's starved for fuel at 45MPH?
    Because he never said it starved at 45mph. Re-read the original post and the problem will become clear...
    2/74 260Z

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    Registered User 5thhorsemann's Avatar
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    My bad, I stand corrected.

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    Registered User Walter Moore's Avatar
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    Oh, After reading my post again, the "lobe" in on the CAMSHAFT pulley, not the crank pulley. (Stupid fingers can't keep up with the brain syndrome...)
    '71 240Z, Because any fool can drive fast in a straight line.

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    so i robbed the coil and resistor off my parts car put them on there and it started to run a little better on the freeway. I could get it to about 75 before it did this. I started driving down to a friends house to get an electronic distributor he had laying around and on my way over it stopped getting fuel pressure and i could barely get it to run at all. im thinking that my gas tank is a lot worse than i thought. im gonna rob the tank out of my 74 260(parts car) and hopefully that will fix it. im gonna clean it out really good before hand though. so between the electronic distributor and the gas tank im hoping this will fix it!! this car has givin me so much trouble its earned the name duh'z's

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    thank you very much by the way everyone for helping me figure out whats wrong with this thing. very much appreciated

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