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Engine Issues at High Revs

Discussion in 'Technical and Troubleshooting Torque' started by nich_s, May 7, 2007.

  1. hi there.

    any pointers on this issue would be great.

    the facts:
    Bike: 1971 CB100
    Great little commuter. Kicks first go, idles great and climbs to town speed adequately.

    Issue: At high revs the engine begins to hesitate/surge/miss etc. This can happen under load or whilst accelerating down hill.

    Please note, i would like to supply accurate RPM but the CB has no tacho.

    Actions taken so far:
    1. New Spark plug
    2. Cleaned Air filter
    3. Drained carb, check for crud. she looked ok.

  2. Engine timing?
  3. Does it have a regulator?

    Some simple voltage checks at idle and again at mid revs wil tell you if it's a reg/rec or battery issue.
  4. Have u checked the jets in ur carbs??
  5. hey, sounds abit like the prob i had with my nsr :? ... i fixed this problem by gettin new spark plug and started using higher octane fuel...its running really fine now... dunno if this helps but it came to my mind straight away...go and check what sorta fuel your bikes is most comfortable with :LOL: cheers, :p
  6. +1 Tweet sounds just like points to me
  7. I'm for points too, probably dirty and incorrect gap.

    Regards, Andrew.
  8. awesome feedback. cheers.

    natta - i haven't checked the carb jets as yet. Got myself some carb cleaner this morning and i shall give it a good clean and inspection tonight.

    cammo - from a quick inspection, and to my surprise i could not see a regulator, just a rectifier, condenser etc. I have tested the 6v battery and it is in good condition.

    nsr150 - when i first got the bike i was suspect about fuel at first too, as previous owner had mentioned it had been there for a while. So early in the part i flushed tank with some methyl ethyl Ketone and then applied some Red Kote tank sealer. i use 95 oct fuel with additive - flashlube. so the fuel side of things should be good.

    the points. i will have a good look at these tonight, going from your feedback it sounds like this could be the culprit.

    thanks again.
  9. On the whole points thing. I actually inspected them a while ago just for general condition no timing adjustments where made etc. But it got my thinking about the possibility of converting to electronic ignition.

    I searched the net and came across The Newtronic Kit - i sent them an email and their response is below.

    ......"The Newtronic kit for your CB100 is a H07 6 Volt kit. Autocar is the new company that has bought the stock and rights to manufacture Newtronic products after Newtronic was liquidated early 2006 and the new company has only just started to get some stock moving. Autocar only sell through resellers. I have no H07 6 Volt Ignition kits in stock as yet, and have to wait until the new company can begin shipping this product....."

    Has anyone used the above mentioned product or has any suggestions on alternatives, should go down the electronic ignition path?
  10. Before you invest the money, replace your lead and/or plug cap. I find most hesitations like this come down to too much or too little resistance in the ignition.
  11. Performed a text book contact points timing adjustment procedure last night (Step by step from the manual) and it was well worth it.

    The points gap, which is meant to be 0.012-0.016 could fit my 0.25 feeler gauge (crazy). So i cleaned the points and corrected the gap to spec.

    Its incredible that with the gap so out that she was running at all. very forgiving i guess.

    Next i checked the timing by rotating the crank and using my light tester on the points, waited for light to go out and checked alignment on crank - which tuned out to be pretty good. no adjustment was necessary.

    She is now a new bike, more grunt from stationary position and smooth as right the way thru the rev range.

    Thanks heaps for all the input. i wouldn't have sorted the issue so quickly without it.
  12. Good to hear, just keep an eye on them, these old ponies are fickle when the gap runs out..