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Thread: SU Carb Guru needed, at wits end!

  1. #1
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    Oct 2011
    jackson, MS

    Exclamation SU Carb Guru needed, at wits end!

    First of all, I recently purchased a 74 260z from a gentleman, the car is everything i've wanted in a Z car, with the exception of a running engine. I've read up TONS of "Search button" topics, and looked all through diagrams of these darn carbs but cannot seem to figure the damn things out.

    The carbs that are on the car are a set of 3 screw bottle top SU's, im assuming late model 72's that the gentleman put on there, when i bought the car, he said i could fill the bowls of the carbs up with gas and it'd run like a champ and that it had only sat up for long enough for the gas to go slightly bad, but the fuel pump wasn't kicking on, so what i did was after purchasing said beautiful car, i went to my local autozone and bought a Mr.Gasket 5-7lb fuel pump, i am now getting fuel TO the carb, but couldn't get the car to run. The engine would just spin over, can spray fuel in it, and it runs off of that like a champ. But soon as the fuel dies out, so does the motor. So in screwing with these things ( not knowing what i was doing) i found out how the choke works on them, (the lever isn't working seemingly) i could pull down on the bottom of them , and the choke applys, i got in the car, and BAM fired right up, until the vibration of the engine closes the choke, and it dies, i let it sit for about 10 min running on its own on a nice warm day (65) and then let the slide back up, and it just died , even under constant rev. I just don't know what would cause that, for them to run perfect up until that point. It had SOME bad gas in it, but the bowls looked clean and so did inside of the carb and needle , no clog between the bowl and carb, due to being able to spray fuel between the both of them and it come out both sides. I just cannot figure it out, is this so simple that im overlooking whats going on?


  2. #2
    Registered User Bcalvosa's Avatar
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    Jun 2003
    New Jersey


    It sounds like the carbs are running lean (because of misadjustment or a vacuum leak), or that the engine is not sufficiently warm to run with no choke. Try googling "tuning Datsun SU carb" for some resources, for example:

    You could also refer to the Service Manual posted here:

    Good Luck,


  3. #3
    Registered User d240zx2's Avatar
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    Sep 2007
    Houston, Texas


    Also get Z Therapy's DVD on tuning SUs.
    First & Third owner of HLS30-00721
    B. 01/70 D. 03/12

    New owner of HLS30-15653
    B. 12/70 D.

    Frank in Houston, Texas

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