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Runs well, plugs foul....

Discussion in 'Norton Commando Motorcycles (Classic)' started by Lineslinger, Mar 30, 2019.

  1. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    Mine correspond including size of new jets.

    You mentioned “floats influencing the needles during riding”.....as in opening too much or simply allowing an irregular/unpredictable flow?
     
  2. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    I suppose next logical move will be to look into the float level adjustment “tool” in the link you offered.
    I was fairly confident I had those floats tweaked properly but will make sure.
    Thanks for your time.
     
  3. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    Is it rich at all throttle positions? You mentioned the
    If you're certain you've eliminated ignition as the culprit (not doubling up on resistor wires/caps etc.), this guide is your friend:

    https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf

    Make sure the problem is at all throttle openings, if so, the float level is the only thing that will effect mixture at all openings, if you can get your hands on a colourtune you may be able to quickly ascertain if this is the case.
     
  4. Danno

    Danno

    Joined:
    Feb 7, 2010
    Try some stay-up floats, Mark. They are easily height-adjustable. Sounds like yours may be a little high. Does it idle without the choke before it's warmed up? If so, drop the float height a bit. It should almost die with no choke before it's warmed up. And I'll front you a pair of Champion N4G plugs. Much less prone to fouling than N7Ys or the equivalent NGK plug.
     
    Last edited: Mar 31, 2019
  5. Madnorton

    Madnorton VIP MEMBER

    Joined:
    Jun 9, 2008
    Doubt it is electrical, the bike would 'rev out' early if the coils and electrics were not up to it. If it still blackens plugs at a stint at WOT then I doubt it is the fuel level. Not been mentioned yet, chokes? as this is affecting both sides, and I doubt both carbs are likely to carry the same fault, or build error if there is any on either carb.
     
  6. tomspro

    tomspro VIP MEMBER

    Joined:
    Jan 25, 2014
    One factor I have not seen mentioned is your altitude.
    I have very similar setup on my 750 and use 200 main jets. Even 190s ran well but would not deliver at WOT.
    I am at 5k so O2 is thin and fuel must be thinned to match.
     
  7. Dances with Shrapnel

    Dances with Shrapnel VIP MEMBER

    Joined:
    Jul 8, 2011
    Always ambiguous (for me at least). So when you state "needles at their upper most setting", I interpret that as the needles are higher thus richer transition and mid range, where most of you street bike business takes place.

    If the needle clip is in the upper most slot, that is the leanest position. If your needle is in the lowest slot it is richer.

    Did you change the needle position (to slot #2) as you had stated earlier and was there any noticeable change?
     
  8. Steves

    Steves

    Joined:
    Oct 16, 2016
    Do you keep your battery on a tender, do you ride with lights on? Sounds you have the carbs covered, so maybe electrical, does tri spark need a good battery? I had a similar problem on one cylinder, turned out to be a bad coil after I had been down the fuel route.
     
  9. Onder

    Onder

    Joined:
    May 11, 2010
    I asked about the exhaust because the book likely is predicated on black caps and cross over. 2a may be different spec. Check.
    If they are Andover silencers they will be fairly unrestricted so Id guess 260 on the mains. Mind that is just a guess.
    But the level of the float will affect how much you need to screw in or out the air mixture screw.
    You need to run up a tube affair as suggested to actually know where the fuel level is not just where the float is. Simple enough to
    do.
    One of the problems of modern nonleaded petrol is you no longer can do a plug chop and get an accurate idea of carb tuning.
    Remember that it isnt just the mains that affect things it is the whole shooting match combined.

    You could test the coil with a multimeter just to KNOW what the ohms are on
    primary coil and spark output.
     
  10. Dances with Shrapnel

    Dances with Shrapnel VIP MEMBER

    Joined:
    Jul 8, 2011
    Unless Lineslinger is running wide open throttle all the time, main jets are not where he should look. I am assuming he's doing street riding which suggests his carbeuration is dominated by slide cut away, needle jet and needle.

    Below is a link to one of the better references on AMAL carbs and tuning.

    https://www.princeton.edu/ssp/65-cub-data/library/amalbritbike.pdf
     
  11. Onder

    Onder

    Joined:
    May 11, 2010
    Agree that for normal street riding you arent into the mains at all.
     
  12. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    I have a tough time interpreting mixture balance at specific RPM,s....

    I’d be willing to buck up for a Colortune if it is a reliable reference. Plugs don’t “read” with Ethanol. Have you used it with success?
    The instructional video looks encouraging.
    I have been using the Princeton Amal PDF as my guide/reference.

    Thank you for the help.
     
  13. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    Chokes have been removed, little to zero cold weather riding and I just never used them.

    Thanks for your thoughts.
     
  14. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    I am in Missouri, 500 ft. Above sea level. I checked around, seems to be a non issue but thanks.
     
  15. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    The needle jets and needles are new with the circlip in the top, upper most notch of the needle seeking a leaner condition.

    I have yet to move it until I can digest the various and helpful information you guys are offering.

    I am still shaking this rebuild down so my riding so far has been very conservative until my level of confidence sets in.
     
  16. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    New battery always on tender. Appreciate the sharing.
     
  17. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    I have yet to put the meter on the output side of the single coil conversion pack (from CnW) but will check.
    I did get whacked by it the other day while pulling a plug wire at idle. Snapped me hard enough for some creative language, but no down side to double checking.
    Interest is appreciated.
    I plan on mocking up a float level check this aftn.
    I keep leaning that direction as my culprit. Thanks.
     
  18. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    Hey Dan,
    My floats and needles are new, but not “stay ups”, do you find these more reliable?
    Inlet needles are aluminum black tipped. New as well, came with the rebuild kit.
    The chokes are gone and it does not idle well until some heat comes into play whereupon it smooths out nicely....but, it does tend to labor or stumble somewhat below 1,000 rpm, in other words it’s not smooth below 1K.
    Might this tendency indicate too much fuel-not enough fair?

    I am running BPR -7ES which I have been cleaning when fouling starts. I have a fresh set of NGK B7ES which I was going to install once I confirm my float bowls are accurate.

    I need to get that horn to you anyway, trade you for the N4G’s?

    Float bowl level is continually noted since I started this thread and I must admit I simply did not give it the attention it obviously requires, maybe the rich condition is that simple?
     
  19. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    I use a colourtune when I need to get a quick idea of whether the mixture is off at a given throttle position, about all it's good for but it does the trick.

    Bear in mind that recommendations "now" being published by Burlen are a bit different than those from the past, or provided by Princeton/Bushman etc... The recommended "Fuel level" (not float height) tends to raise the float some distance above the bowl edge, though the carb body is recessed enough on the underside to allow this, just make sure there's no fouling if you get it to the suggested level. I've got my "float height" set pretty much level with top of bowl if not not slightly above, runs well, but I know it's technically still below Burlen's fuel level suggestion... these carbs are pretty rudimentary when it comes to "fine tuning", more wooden stick than Stradivarius

    You don't need to mock up any fancy rigs, just get the fuel in the bowl till the valve shuts and measure down from top edge with a business card cut into a "T" shape.

    Any chance you are running a kill switch?
     
    Last edited: Mar 31, 2019
  20. Lineslinger

    Lineslinger VIP MEMBER

    Joined:
    Feb 26, 2017
    You are correct. The Princeton PDF has been my go to reference. Thanks again.
     

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