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Engine revving

  1. Aug 28, 2013 #1
    I am facing this RPM problem with my single-cylinder engine(Duke's) that I have used in my project..
    Even though the ECU is programmed to allow RPM upto 12,000 revs but still engine can only reach 6,000 when the clutch is engaged...it can go near to 12,000 only while the clutch is disengaged. What can be the reason for this...
    Also , when I disengage the clutch, a sudden large amount of air is sucked in.:confused:

    P.S. - The engine is also having problem of unburnt smoky fuel coming out of the intake port, which I guess is due to the exhaust back-pressure as the exhaust pipe & muffler is custom-built & not the engine's standard one.
  2. jcsd
  3. Aug 28, 2013 #2


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    I guess the obvious reason you can't get to 12000 RPM when driving a load is because the engine can't generate enough power.

    You shouldn't be getting "smoky fuel" coming out of anywhere, and if it's coming out of the intake port something is badly wrong - e.g. the timing is so wrong you are getting combustion while the inlet valve is still open, or the inlet valve and/or spring is damaged. I think you need to sort that out first, before you worry about back pressure from your exhaust etc.

    But you can easily check if your custom exhaust is causing the problem - just disconnect it (and wear ear protectors when doing the test!).
  4. Aug 29, 2013 #3
    It can't be the inlet valve/spring as the engine is brand new one...but I'll check it anyways.
    And now I see that both power loss & smoky fuel problems can be due to improper valve timings & of course the exhaust is faulty too.
  5. Aug 30, 2013 #4
    Ain't no expert but this is what I observed in the shop:
    Can the ECU be connected to a laptop using a OBD(on-board diagnostics) plug? In that case,you could use a program to adjust the timing(never done it myself). Or,you could play around with the distributor after you short-circuit(paper-clip) the ECU adjustment connector.
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