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Almost Stranded

Discussion in 'Norton Commando Motorcycles (Classic)' started by cliffa, Dec 29, 2017.

  1. worntorn

    worntorn

    Joined:
    Dec 22, 2006

    Many years ago Dyno Dave measured the advance curve produced by Boyer, Lucas Rita and the standard points auto advance unit.
    It might surprise you that the Boyer and Lucas Rita have quite nice gradual advance curves with the Boyer being the more gradual of the two. The Boyer curves to full advance by about 2500, while the Rita curves to a greater full advance by about 2350 Rpm.
    The Commando points / auto advance unit tested is almost an on/off switch, very harsh , no curve at all just a quick slope up from full retard to full advance by 1450 rpm.

    Every AAU I've played with works this way. Its the nature of the beast, but relatively low tune engines such as the Commando engine seem to tolerate it ok.
    The gradual advance curve of the Boyer has to be an improvement on the AAU on/off switch though.

    Glen

    http://atlanticgreen.com/boyerexposed.htm
     
    Last edited: Dec 30, 2017
  2. cliffa

    cliffa

    Joined:
    May 26, 2013
    Do they vibrate ?
     
  3. WZ507

    WZ507 VIP MEMBER

    Joined:
    Dec 26, 2013
    Glen, with respect to the various advance curves you cited I think you may have missed one critical point and that is that for some reason David chose to use “distributor degrees”, by which he must mean cam degrees, as the standard Commando automatic advance unit (AAU) curve is fully advanced near 3000 engine rpm, which is consistent with the subject plot showing full advance at 1450 cam rpm. Thus the Norton AAU does not come in suddenly from idle to full advance at 1450 engine rpm, but rather at 3000 engine rpm. In my mind the AAU is in fact a very nice advance curve, as are several other EI curves, and the Boyer is the odd duck that unnecessarily trickles on forever and doesn’t provide maximum advance until it is in the 5000-6000 engine rpm range (consistent with David’s plot showing the Boyer still advancing at 2500 cam rpm, i.e., 5000 engine rpm).


    In the past one of our contributing forum members, “rick in seattle” posted a variety of common Norton advance curves in engine rpm. Regrettably, as far as I can gather, these curves have all fallen victim to the PhotoBucket fiasco, thus are no longer present on the forum. However, I did make copies of 2 of them but do not have proper context surrounding the advance curves other than to say Rick had measured some and David Comeau had measured some and Rick compiled them all in a variety of XL plots. I believe as new ignition systems were introduced and accompanying data generated on said ignition systems Rick updated the plots. I wish I could tell you more about the subject plots, but can’t associate them with any particular forum entries at this juncture, so they’ll have to speak for themselves.

    Rick in Seattle Advance Curves.jpg

    Rick in Seattle Advance Curve Update.jpg
     
    Last edited: Dec 30, 2017
  4. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Yes, I did miss that, my apology.

    The auto advance units I'm familiar with are admittedly somewhat worn, but when strobed do act much like an on/off switch.
    It doesn't seem to matter much though, the engines tolerate the quick shift to full advance just fine.
    Even with full advance at all rpm (eg. Joe Hunt mag) these old engines seem to be happy.

    As to the Boyer robbing power, that is possible but I would be quite surprised if the dyno showed that.

    Glen
     
    Last edited: Dec 30, 2017
  5. Fast Eddie

    Fast Eddie VIP MEMBER

    Joined:
    Oct 4, 2013
    Mine also suffered the broken wire on the back plate, that particular failure mode must have caused lots of grief over the years as, you can look at it a dozen times and think it’s OK, only when you remove the back plate and cut off the tie wrap, do you realise the truth. I bet many an otherwise good bike has been consigned to the back of the barn / shed for this!

    As to the Boyer costing power, I don’t know if anyone has evidence of this on a Commando? It would be interesting to see if they did.

    Sorry to repeat this for those that already know, but I definitely had that issue on a big, highly tuned triple. The Boyer on those runs a triple wasted Spark, and 4 volt coils. I’m no electronic wizard, but to my layman’s mind it just didn’t have enough concentrated spark power at high revs.

    A Tri-Spark with a dedicated Spark, and dyna coils, yielded a 5bhp gain all by itself.
     
    Last edited: Dec 31, 2017
  6. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    The subject of points ignition vs Boyer came up at a local gathering last year. Dave Wildman was present. He was always the one to beat at Westwood, a great rider and tuner.
    Back in the 80s, his sidecar passenger convinced him to replace the Triumph Trident's points with Boyer.
    Dave tried it as an experiment but fully expected some power loss. Instead he got 400 more RPM on the straight!


    http://canmoto.ca/dave-wildman-class-of-2010/

    Glen
     
    Last edited: Dec 31, 2017
  7. norton73

    norton73

    Joined:
    Dec 11, 2008
    cliffa likes this.

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