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The VF 1000 enigma

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by techno, Dec 9, 2005.

  1. Ok, I am throwing this one open to the collective mechanical knowledge that is the netrider members. This one has me stuck.

    I own a 1984 Honda VF1000F, the one with cam chains, not gear driven ones. A few months ago, the motor died. I managed to pick up one from a wreckers interstate. I was assured it was running fine. It was from a 1985 VF1000F but I don't think there are any differences apart from the routing of the water pipes.

    I put in the new motor and it starts and runs OK at idle but when it gets to approx 2800 rpm it runs really rough and won't rev any further. If I let off the throttle it returns to idle OK but will do the same thing again even if you rev it quickly or raise the revs slowly.

    I put the carbies on from my old motor as they were a known quantity. The ones with the new motor needed a good clean.

    Because I have a spare motor that I knew ran OK I have changed the following parts -
    Spark plugs, leads, coils, pick up generators.

    I have run it with and without the airbox/filter.

    I have taken off the carbies and checked the boots for leaks.

    I have drained the tank and float bowls and put in fresh fuel.

    I have run it long enough for it to warm up properly.

    Nothing seems to make any difference. I took it to a mechanic who fiddled around, told me he didn't know and to come and pick it up and then tried to charge me for the experience.

    As I have the old motor I am going to hook it up to the bikes electrics and fuel supply to see if it suffers from the same problem. This might help with diagnosis.

    I suspect its electrical due to it only arising at a specific rev rate.

    Anyone have any reasonable ideas other than setting fire to it?



  2. It could be a lot of things. It could be plug break down under load.

    Try new plugs and make sure the gaps are right.

    It could be bad leads. When lead get a old they build up a resitance and behave a bit like this.

    Check vacuum lines.

    How were the cams on the new motor? Maybe you have no lobes left.

    Is there some way of getting the ignition advance backwards on these motors?
  3. i would be looking at vacuum, but you've already gone over that pretty well :?

    my limited experience has had that happen to me once. my GFs XJR didn't want to rev over 5k after i cleaned the carbs, didn't matter if i was climbing slowly, quickly or without any load at all, 5k was where it stopped.

    pissed around with a few things, but ended up thinking i should maybe hook the airbox back up. ran like a dream again after that :?

    probly not any help, but i like telling stories :LOL: