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Pinging when warm

Discussion in 'Other Norton Motorcycles' started by Paul W., Jun 7, 2018.

  1. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    The N15 starts spark knocking after the engine warms up. Any thoughts as to which direction I should go first? I’m thinking I should adjust carb air/fuel mixture first.
     
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  2. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Start with the service items: points, ignition timing, valve clearances.

    Yes, it may be a weak mixture. Did it always do this pinging? Has someone dropped the needle down in the clip?
     
  3. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    I assume, you are using four star gas/petrol fuel?
     
  4. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    I just picked up the bike a month ago. I rebuilt the carbs, sleeves, jets, needles, etc., so the needles could need adjusting. I have no idea what was done to the bike the past with regards to rebuilds.

    As for the petrol, I get it at the co-op, because it’s non-ethanol. It runs fine in my Harley, which pings with low octane, and my XS650. I think they have a higher octane non-ethanol fuel there. I’ll give it a try.
     
  5. Bob Matthews

    Bob Matthews

    Joined:
    Dec 19, 2016
    The very first thing I'd be doing would be to retard the ignition a couple of degrees.
     
  6. norton bob

    norton bob

    Joined:
    Nov 29, 2013
    That may work,I had to reduce the CR and widen the exhaust seats on one engine,weak mixture wont help.
     
  7. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    I was able to get out and turn some wrenches on the scooter today. I raised the needles up one notch each. It actually seem to run better, but once again as the bike warmed up, it started to ping again. I was also running higher octane fuel in it. The plugs definitely showed signs of a lean air fuel mixtrue before the swap. I need to buy more plugs and run it again to see what’s going on. As of now, I don’t think they are related.

    Bob, when you say you had to reduce the CR, are you referring to compression ratio?

    To enjoy a little riding in today’s gorgeous weather, I took out the XS650 for a ride. The left side vs. right side shift doesn’t affect me, but the 1 up and 3 down vs. 1 down and 4 up sure gets confusing when switching back and forth. :/
     
  8. norton bob

    norton bob

    Joined:
    Nov 29, 2013
    I am about to fit a compression plate to our Atlas to get back to what the engine designer thought best. Valve seats are the conduit for the heat of the exhaust valve (which can cause pinking). Look for sharp edges to plug hole,and piston crown.
     
  9. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    Check ignition fires 28 degrees on both plugs with a timing disc, if you have 9;1 ;1 pistons, if you have the original concave pistons of 7.5 ;1 the timing should be 32 BTDC -you have not stated if you have a K2F magneto- which are notorious for not firing at 180 degrees apart.
     
    Last edited: Sep 4, 2018
  10. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    It's got a Joe Hunt magneto.
     
  11. mdt-son

    mdt-son

    Joined:
    Jan 19, 2012
    I second the above. The likely causes are weak mixture or delayed ignition on one cylinder, assuming your petrol is at least of 95 RON octane. You shouldn't need to lower the CR ratio if your engine is to factory spec (7.6:1). Maybe the knocking has to do with excessive carbon build-up? If flakes of carbon start to glow, they may cause the combustion gas to ignite, i.e., cause pinging.
    Of course, carbon build-up has other historic causes. An examination of the combustion chambers by use of a borescope is probably worth doing, as you have no knowledge of the bike's history.

    -Knut
     
  12. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    And, these never go wrong?
    Ignition timing should be set at 32 degrees for 7.5 1 concave pistons and 28 degrees for 9:1 flat top Commando pistons.
    9:1 pistons require 98 octane or better Fuel/gas/petrol.
     
  13. norton bob

    norton bob

    Joined:
    Nov 29, 2013
    Very few Atlas motors still run with the hollow crown low compression Ratio.
     
  14. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    Not sure where you got that from. I was ansswering a previous post.
     
  15. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    So I was finally able to time the bike and get it back up and running during a hectic summer. I times it with a timing wheel within 1/2 a degree of 32TDC. It still pings some, but less than before. I’m going to give higher octane fuel another shot and see if there’s a difference.
     
  16. dynodave

    dynodave

    Joined:
    May 28, 2003
    Joe Hunt?
    Lots of theoretical and practical problems are possible.
    No specific experience here but...Is it a taper shaft mag with LUCAS AAU?
    1. Poor condition sticky AAU can fail to retard leaving it over advanced. ping
    2. Incompatiable LUCAS device might have to much mechanical power to advance Joe Hunt armature result is advancing to early. different devices have different mechanical/magnetic drag which must dynamically be over come by the AAU weights. ping
    2a tired/stretched AAUsprings...

    3.full advance @ high RPM is likely to be to much if 32 degrees. ping

    4. A straight shaft mag with a fixed gear set to 32 degrees is absolutely too advanced for lower RPMs except at low dynamic pressure, light throttle openings. ping
     
  17. Paul W.

    Paul W.

    Joined:
    May 12, 2018
    Dave,

    Yes, it has a Lucas AAU. I put new springs on it and it seem much tighter. I also checked to make sure the magneto advanced when the AAU weights were out, so that’s not an issue. It’s static timed at about ~31.5 TDC with AAU fully advanced, which is definitely close enough. I see a post above mentions 28 BTD. Now I wonder if I should have researched that scenario before I reassembled it. I’m going to fuel it up with higher octane fuel today and take it on the hilly backroads to see how she does. I’ll be reporting back this afternoon.

    Thanks!
     
  18. Beach

    Beach VIP MEMBER

    Joined:
    Aug 27, 2013
    Intake leak? Have you checked?
     
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