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Thread: hitachi su carbs(spl311)

  1. #1
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    hitachi su carbs(spl311)

    what seems to be the problem on this, the engine idles good and revs smoothly but is having a flat spot around 3800 to 4000 rpm and it can't rev further than that, it already got new fuel filters, fuel hose and a cleaned up tank and lines, any help and input would be appreciated

  2. #2
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    Check to make sure your distributor is pulling full advance, I bet its not. If it is, you might be going a little lean on the mixture, fatten the mixture up by turning the fuel adjustment on the underside of each carb.

    You want to be at 16 degrees at 750 rpm, 36 degrees 4500.

    Will

  3. #3
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    Vacuum Advance

    The roadster used two different methods of hooking up vacuum advance to the distributor. First one was a simple striaght tube system joined to the rear SU with a simple vacuum hose jumper. The later system used a flared attachment with the nut on the vacuum line. If you have the early version, check to make sure that your vacuum hose hasn't dried out of indeed may be missing. Flair? Check that it is still connected.

  4. #4
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    thanks for the replies, i've checked the timing advance and the vacuum lines and its all good, i did fatten the mixture and it slightly got better but it still eventually getting a flat spot, i think its having some fuel shortage or something

  5. #5
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    I seem to have a similar problem with my engine. The next things to check for me will be the needle valve in the float chamber and whether there are air leakage at the carbs at high rpm. I hope it could help you.

  6. #6
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    I talk about the needle valve because of the important notice written in this webpage: http://www.teglerizer.com/sucarbs/techtip6.htm

  7. #7
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    Quote Originally Posted by mitx
    I talk about the needle valve because of the important notice written in this webpage: http://www.teglerizer.com/sucarbs/techtip6.htm
    thanks for the link

  8. #8
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    Maryland
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    take off the air cleaner and rev it up to the flat spot. Place your hand in front of the carb (blocking that air) and see if it goes higher. If so, your needle is bent.

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