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1967 N15: spark plugs very very full of soot

Discussion in 'Other Norton Motorcycles' started by pierodn, May 25, 2018.

  1. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Bike has the stock 1967 Amal 930/7/8 concentric with 220 jets, 25 pilots, slide cut 3, needle jets 106, needles central position.
    Float bowls 2 mm under the top flat.
    Air way well cleaned, carb cleaner spray trough all the holes.
    Bike has Pazon sure fire I.E. setted 31 degree BTDC.
    Engine has all parts new: pistons, valves, guides, etc.
    The bike starts first click and runs great up 2000 rpm but under has a flickers.
    The spark plugs (NGK B7ES) are very full of soot, very black.
    I start with air unscrewed 1,5 but it is the same with 2 turns.
    What i must check?
    Thank you.
    Pieto
     
    Last edited: May 25, 2018
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    p400 likes this.
  2. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Original type 1967 carbs? So are you using the short main jet holders and two-stroke type needle jets and suitable needles?
    Are the needle jets new?

    At what throttle opening does it soot the plugs?
     
  3. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Yes.
    All original parts.
    Short mai jet holder.
    Needle jet not new and neither main jets, pilot jets, and throttle needle. (
    Needle jets 106 dont have the two holes on the sides.
    New only float bowls and float needle.
    Plugs well soot after a riding of ten minutes to 2.000/3.500 rpm.
    Thanks.
    Piero
     
  4. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    It's best to mark your throttle so you can tell what position your carburetor is in to find where it is running rich,
    It's much easier doing it this way because you need to know what jet to change/replace or needle position etc
    This has nothing to do with rpm , cheers
     
  5. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Sorry but i dont understand the way “to mark the throttle”.
    Ket me understand better how do you do it.
    Thanks.
    Piero
     
    Last edited: May 26, 2018
  6. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    Needle jets wear in use. That makes the mixture rich at around 1/8 to 1/3 throttle.

    Buy new needle jets of the correct type from Hitchcocks, Surrey Cycles, or Amal, not from Norvil.
     
  7. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    Adjust your idle screw all the way out now take up the slack in the cable and make a mark on the twist grip and twist grip housing this will show throttle shut position,
    Now open the throttle until the very bottom of the slide (not the cuttaway) is level with the top of the carburetor bore,
    This will show throttle fully open,
    Now mark half way between the two marks
    Now half way between those two
    This will give you the closed position /quarter position/half position/ three quarter and full throttle
    You can mark it with tippex or used masking tape etc
    You can run the bike at these throttle postions and check the plugs to see exactly which is giving you the rich running, of course that's if it is a carburettor fault , hope this helps
     
  8. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    I agree that's probably your problem Pierdon the needle jet makes a huge difference,
    And if you mark your throttle you will see how much time you ride at an 1/8 throttle
     
  9. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    Do you think is better to change the early jet holder with the later one?.
    Could be better to change the throttle needle also?.
    Thanks.
    Piero
     
  10. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi.
    I understand.
    Thank you so much.
    Piero
     
  11. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009

    I don’t know. If original Atlas-engined bikes with the old setup usually run well, then there’s something to be said for not updating.
     
  12. Bodger

    Bodger VIP MEMBER

    Joined:
    May 9, 2017
    Not sure what is happening from your description. Do you mean the bike runs ok up to 2,000 rpm and then has a flat spot (stumbles/hesitates or won't accelerate)? I think the bike is just coming on to the needle jet at that rpm. An interesting and easy experiment would be to raise the needle jets one slot in both carbs (richer) and see if it stays the same, gets worse or better. If it stays the same or gets worse you could try going one notch leaner than the stock specification . In my experience one notch either side of the standard setting is often better than the standard setting. I'm guessing that petrol formulations were a lot different 50 years ago.
     
  13. Bob Z.

    Bob Z.

    Joined:
    Mar 30, 2012
    I suggest you move the needle clip to the top notch to lean the mixture.
    If your needle jets have the thick top opening, those are the oldest style with no side holes.
    Also you can try the longer jet holder and needle jet with the hole in the side.
    The longer jet holder places the main jet lower down into the bowl.
    One more thing to try is to open the newer needle jet hole to o.90 mm.
    This was recommended in one of the Amal Concentric tuning guides to lean the mid-range mixture slightly.
    See my photos below. I hope this helps.

    [​IMG]

    [​IMG]
     
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  14. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi All.
    Thank you so much.
    Piero
     
  15. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Hi All.
    Carbs overhaulled again.
    New 106 later tipe with holes both sides, new throttle needle central position, new long later jets holder, new 220 main jet, new 25 pilots, new NGK B7ES spark plugs.
    New float bowls 2mm under the top with new vitons.
    Pilot Air screws unscrewed 1,5 turns from tight.
    Air way recleaned and opened.
    The bike starts first kick and runs well, no more stumbles or hesitate.
    But, after a running to 2/3000 rpm the right spark plug was near pefect but the left was always fool of soot!.
    Soot, not oil.
    Then, to see if was a fire probkem and not the carb, i have changed the spark plugs with new one turning the coils.
    After a mid range running nothing is changed.
    Why right works well and not the left?.
    What i must check more?
    Thank you for your precios advices.
    Piero
     
    Last edited: Jun 1, 2018
  16. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    Piero:

    Try turning left pilot air screw open to 2 1/2 turns. Report back.

    Slick
     
  17. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    I will do it.
    But where is the problem?.
     
  18. texasSlick

    texasSlick VIP MEMBER

    Joined:
    Jan 2, 2013
    As I see the problem, you are too rich on the left cylinder because:

    1) not enough air from pilot air screw, or,
    2) too large a needle jet

    I do not think 2) is the problem, as 106 needle jet seems right, and you have reported they are new.

    Is there any possible way the right needle is excessively worn, or perhaps not the proper taper?

    Slick
     
  19. pierodn

    pierodn

    Joined:
    Nov 10, 2012
    Carbs overhaulled both with all new parts.
    Why there are differences from right and left?
    Piero
     
  20. Triton Thrasher

    Triton Thrasher

    Joined:
    Feb 10, 2009
    You don’t just set pilot mixture screws to a turn and a half out and leave them.

    You adjust them for correct mixture at idle. Am I being too obvious?
     
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