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Tuning the ATU (Mechanical Advance)

Discussion in 'The Garage' started by XS650D, Aug 9, 2019.

  1. XS650D

    XS650D XS650 Junkie

    I had some electrical issues earlier in season which are all behind me now.
    Unfortunately I fried my Electronic Advance in the process and had to reinstall the mechanical unit. I still have the pamco Electronic Ignition.
    Seems that XS650 Direct here in Canada does not carry just the Advance,u need to
    purchase the entire system, regardless I am stuck with the MikesXS/xs650 direct advance springs
    with the issues of either to tight or to loose. Is there a recommended rpm that the advance should start.
    Ive read that it should be approx 1700rpm to approx 3200 rpm at max advance. I noticed that when the
    electronic advance was installed and working the advance would spool up gradually or progressively and
    seemed to help smooth out the power curve off the line in low gear. Is that generally what we want to happen
    with the mechanically springs/weights. I realize the weights should snap back when released but the trick seems to be getting the weights to advance from idle smoothly and progressively. Currently after cutting and stretching the springs back and forth ive been able to adjust the tension so they snap back when released but will advance or open when u add any throttle at all, only issue is I reach max advance at approx 2500 rpm, will this be ok or what issues will I have. I started playing with the advance as I seemed to have a bit of a flat spot between 2000 and 3000 rpm that I could not dial out with carb changes. (my Timing is bang on) I had my advance springs set way to tight I think as I was more concerned that the weights snap back or return .It was like all or nothing ,under 3000 rpm nothing then Wam! It seems better now but still a little flat. Worth mentioning is I have the 17/33 gearing, not sure if 1st gear will be slightly less snappy.Ive never tried the stock 17/34 so cant compare.Any advise would be great. At least im riding my bike now every day, had approx 3-4 weeks with issues and no riding,that really sucked! Also does valves being set to spec have any effect on bottom end.Is been approx 1000 miles since ive checked them.
     
  2. 5twins

    5twins XS650 Guru Top Contributor

    17,776
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    Your advance seems about right now. Personally, I like the original springs. I know they're not available any more but they do come up on eBay from time to time. You might look occasionally for them.

    Sometimes original springs get replaced when they're not actually the problem, lack of lubrication is. I keep my original advance well lubed and while it has loosened up due to age and use, it still seems to work fine. I don't think the original springs snap it back really tight anymore (maybe they never did?) but the timing fully retards OK. Revs drop to idle speed like a rock and don't hang at all. That tells me the timing is retarding as it should.
     
  3. XS650D

    XS650D XS650 Junkie

    K Thx for advise 5 T
     
  4. XS650D

    XS650D XS650 Junkie

    Found a set of used springs on EBay but with shipping, duty and taxes it’s dam near $60 Cdn For $30 more I could get a brand new Electronic Advance if Mikes would ship here. We’re do people come up with these prices Lol
     
  5. XSLeo

    XSLeo XS650 Guru Top Contributor

    Concerning your flat spot, What air filters do you use? If pod filters the style of pods can effect the way your bike performs.
    The short tapered pleated element style pods, K&N and similar pods cause excessive air flow turbulence through the carb. This effects slide lift. This causes a flat spot in the rom range your mention.
    A longer straighter pod o that type may improve things but doubtful. A longer straighter foam pods will improve it.
    These foam pods have a smoother air flow through the carbs.
    I and others have had trouble with the K&N type pods. Couldn't tune out the flat spot. Other on here said the foam pods fix this. I swapped my K&N's for UNI Filter foam pods and viola no flat spot.
    Greatly improved the way the bike ran.
    Leo
     
  6. 5twins

    5twins XS650 Guru Top Contributor

    17,776
    7,584
    688
  7. XS650D

    XS650D XS650 Junkie

    I have the Uni Filters. I got the springs now opening at approx 1600 Or just of idle and totally open around 3000 rpm BUT u will get a good laugh when u see the condition of the springs now after butchering them. It’s working better but still doesn’t have the snap an feel above 3000 when the needle starts to flow!
     

    Attached Files:

  8. XSLeo

    XSLeo XS650 Guru Top Contributor

    Well, it sounds like your ignition is working well. If it's still not running ell it may be time to revisit your carbs.
    Leo
     

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