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Thread: 1971 Datsun 240Z Carb Question

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    Default 1971 Datsun 240Z Carb Question

    OK....New to the Datsun world. Have some questions. The car has a totally rebuilt engine, but it hasn't been run in about 3 years. When we went to start it, fuel comes out of the hose that's connected what at first thought was an overflow valve. But, upon reading, that's not an overflow.....It looks to be an air intake. We actually clamped them (there's 2, one on each carb), and the car started right up. But now gas leaks out the float....perhaps a bad gasket. But my wquestion, why does gas come out of these tubes. If it's an intake, it should be sucking in air. What if there's not enough oil in the reservior. Why is there oil in the reservoir??

    I'm lost.
    Last edited by KidStallyn; 12-24-2010 at 09:34 PM.

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    Default carb problem

    OK lets start with some clarrification. Are these the stock SU carbs? I will assume they are, the damper rods that screw down in to the domes on the top of the carbs need oil in them. They only need so much and the right viscosity. The oil makes the piston rise and fail a little less dramatically. Makes the throttle easier to control and prevents stalling when the throttle is dropped closed. The wrong oil changes all of those things. If the tubes your are talking about come off the top of the float bowls and attach to the back of the air cleanner housing if I remember correctly they are overflow lines / vent lines. If fuel is coming out of them I would think the needle valve above the floats are stuck open and the float bowls are flooding ( one other possibility would be too much fuel pressure; electric fuel pump with no regulator). If they are flooding clamping them is not going to help because the fuel has to go somewhere. Find the problem. 3 yrs is a long time for carbs to sit. Did they have old gas in them? Is there old gas in the tank/lines? Get it all out. The newer fuels have oxidizers in them that promotes cleaner combustion. It also means is goes bad quicker. Think rust for gasoline. The fuel turns to varnish, gets gummy, more orange and has a distinct bad gas smell. You may need to clean your carbs, but if you disassemble them, you need to prepare first. You need a service manual. Read the carb section a couple of times . Only disassemble one carb at a time. Be carefull and don't use abrasives on the surfaces, and DON'T BEND THE NEEDLES
    Did that answer your question?
    Charles

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    Default

    Thanks so much for the reply. We have two service manuals, and after a lot of readin of those sections, I agree with you diagnosis. The tube I'm talking about are on the top, and would goto the air cleaners if we had the stock air cleaner. The air cleaners on there are not stock, and there are two individual air cleaners. The gasket seal on the front carb is dried out. The car sat garaged for three years, with an empty tank. There was less then a gallon of gas in it. Which was def bad. We had thought we'd gotten it all out, but I'm sure there was some left in the carbs that gummed them up. I'll be taking them apart 1 at a time today to clean them up. Also, we aren't using an electric fuel pump, just the stock mechanical.

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    Default

    Those so called air intakes are actually the bowl vents, all carburators have them and should not be plugged. There must be atmospheric pressure on top of the fuel for it to be drawn into the airflow through the venturi (Bernoulli's Principle).

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    Default

    Once you take your carbs apart be sure to do three things - research - research - research. You will need to make sure to adjust several settings - replace your float bowl gaskets - reset your floats and so forth. If your floats are set too high the fuel will come out of either your carb(s) or your overflow hose. If your floats are set too low your engine will not have any performance or loose torque and fuel at any random RPM. Be sure to do your homework before you start so you understand the process and what items to have on hand to get your setting finalized correctly. All this has been discussed in detail in the past along with the FSM............the joys of S.U.'s!!
    Life's a journey; enjoy the ride!

    Mitchell
    L28 - N42 Block w/Flat tops - N42 Rebello Head & Cam - Triple 40 PHH Mikuni's - Headers - Recaro Seats -
    R180 3.9 Diff - Close Ratio 5 Speed - Toyota Vented Brake Upgrade w/ Porterfield High Performance Pads & Shoes

    1972 Datsun 240z
    HLS30-75040


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    Default

    Muck out the needles and seats that screw up into the float bowl lid w/ carb cleaner to cut any sticky fuel varnish and try it. As has been discussed more times than I care to admit, there should be no reason to assume the floats need to be adjusted when all they've been doing is sitting. More unintended carb problems have been caused by fiddling with float levels than have been solved by fiddling with float levels.
    Bruce Palmer
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    Quote Originally Posted by Travel'n Man View Post
    If your floats are set too low your engine will not have any performance or loose torque and fuel...
    ...or cause the car to not even start.
    Gary
    Guardian of HLS30-91415
    Previous Owner of a 10/70 240Z ('83-'85)

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    Found a rebuild kit at CarQuest and they had it delivered form Phoenix the same day. Rebuilt the carbs yesterday and re-installed them. Took a minute, but the car started up, and I adjusted the idle and she runs like CHAMP!!! Now, I have to go through all the fun of getting it registered in my name and plated....go through the emissions testing, etc. Since the entire engine is rebuilt, I don't expect it to fail emissions....but you never know. I'll make sure the engine is warm etc.....

    Right now I have it idling about 1100. I know that's a bit high, but at 750ish, like the manual says, it really sputters a bit....especially when I press down the gas. I need to wait for the temperature to rise before I can make any final adjustments.

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    Properly tuned SU's will idle silky smooth at 500 rpm. At least mine does. You need to go through the complete SU tuning procedures. Get your air flow right first, then get your mixture right.

    A healthy engine will not get you through your emission testing, your carbs will make or break you. Spend a day researching on this forum or better yet, but the JUST SU's DVD that Bruce and Ztherapy sells. It is required watching for any Z owner.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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