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73' Norton Mark I Running Rough

Discussion in 'Norton Commando Motorcycles (Classic)' started by Eric Bauer, Jan 26, 2020.

  1. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    Hey guys, having issues with my new (old) commando. I bought it a couple weeks ago with 12,014 miles on it - all of the work below had been done to it at 12,000 miles right before i bought it by PO (notes are from mechanic). It has been running great and I have actually been using it as a daily driver. It currently has 12,200 miles on it. Went on a 30 mile ride yesterday and it was running great. Then out of nowhere it has just started running rough. Hard to start (was relatively easy) and it will sometimes die at idle. Decent amount of backfiring out of the right cylinder. I thought maybe it was just the change in temp (In Phoenix so it goes from 45 - 75 degrees daily) but its still running rough. Runs clean above 3,000 RPM so thinking its the idle circuit. So this morning went and got some carb cleaner and have a tool the mechanic gave me and cleaned out the idle jets on both carbs. Reset the idle to around 1,000 by tweaking the carbs but if I go around the block it still backfires out of the right cylinder and then when I park and put it in neutral the idle hangs quite high at like 1,500 RPM and won't settle back down unless I tweak the carb screws. Any thoughts? I've dealt with Amals on my Triumph Daytona T100R but never had the backfiring before. Below is a list of all the work done. Thanks ,Eric

    Work done: New plugs, new battery, set timing (Boyer EI), cleaned carbs, new plugs, new wires. Set valves
    I took a look at your bike this morning:
    1. The rear tire is a tire made for front wheel usage. It is installed "backwards" as the rotation for the rear wheel is reversed from the rotation for the front wheel. EX: The front wheel is "pushed" by the road. The rear wheel "pushes" against the road.
    2. Both the front and rear tires should be replaced anyway as they are beyond the recommended 4 to 7 year lifespan for tires.
    3. For the "Tune UP" I will check/set the valves, clean the carbs, check the ignition timing, install new plugs, and change all the oils.
    Made a battery restraint. Pulled the air cleaner and cleaned it. Pulled the carbs, disassembled them, and cleaned them. Rerouted the rocker oil lines. Rerouted the crankcase breather tube. The carb needles are worn beyond reuse. I have a friend who stocks Brit-Parts and he has new needles. I will get two new ones tomorrow.
    Tomorrow: Reassemble and mount the carbs. Set the valve clearances. Change all the oils. Reinstall the tank and gas lines. Install filters in the gas lines.
    Bought new carb needles and reassembled the carbs. Installed the carbs. Lube'd the carb and choke cables. Checked the valve clearances and found them ok as is. Bought a new side cover twist lock assembly and installed it.
    Tomorrow: Change all the oils. Reinstall the tank and gas lines. Install filters in the gas lines.
    Checked Static Timing. The bike will run at this setting, but the timing will be rechecked with a strobe light for greater accuracy. Drained and changed the fork oils, the primary case oil, the engine oil, and the tranny oils. Installed a new oil filter. Installed the gas tank. Installed the gas lines. Installed in-line filters in the gas lines. Installed the %^$#& stock air filter assy. Made new spark plug wires. Checked the front brake switch. It was bad.
    Next: Purchase new brake switch locally if possible, if not order it. Start the bike and strobe check the ignition timing.
    I found a brake switch locally and bought and installed it. I bled the front brake system. Started the bike and strobe set the ignition timing. Set the pilot air mixture and idle speed. Installed the side covers and seat. The bike is ready for a ride test. I will try to get that done today.
     
  2. kommando

    kommando

    Joined:
    May 7, 2005
    What was this special tool for the idle circuit, unless it was a #78 or 16 thou drill then it will not be 100% reliable in cleaning out the pilot jets (assuming they are 25 pilot bush jets in pre premiers or 17 pilot jets in Premiers. A probe will remove the crud but also push it back into the feeding galley and then it comes forward the next time the bike runs and gets into the pilot jet again. The drill puts the crud into the flutes and then drags it out when withdrawn. If the mechanic also used a probe then that would explain the pilots being blocked again within 200 miles.

    You also need to check the pilot air and fuel galleries plus the 2 holes out of the pilot mixing chamber into the main venturi.

    For how to do that

    http://www.jba.bc.ca/Bushmans Carb Tuning.html

    and study this diagram

    [​IMG]
     
  3. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020

    Thanks for your reply. The tool is basically a wd-40 plastic tube with a guitar string on the end for lack of a better term. He comopetely disassembled and cleaned the entire carb, albeit that was in October and it sat for a while, but it has been running fine since I got it - is it possible (or better said, likely) for those other parts in the carb to get gummed up that quickly? It really hasn't been sitting for more than two days in a row.
     
    Last edited by a moderator: Jan 26, 2020
  4. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    Try switching plug wires side to side and see if problem goes to opposite side
     
    998cc likes this.
  5. kommando

    kommando

    Joined:
    May 7, 2005
    It is as I suspected a probe, it does clear out the jet but the dirt it removes gets pushed back into the feed gallery, when fuel starts to move forward next time the bike runs it moves the dirt back towards the pilot jet and blocks it again. So repeating myself the only reliable method is with a 16 thou drill, it has flutes in the sides which fill with dirt and then when you remove the drill the dirt comes out in the flutes, you wipe the drill clean and its ready for another clean out.
     
  6. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    Yes, I have a drill bit at home which is what I use but I am currently working out of town and bought the bike here on happenstance so just trying to see if it could be something else given this just had the carb disassmebled and cleaned out. Unfortunately I dont have my tools and the probe is the best I have.
     
  7. kommando

    kommando

    Joined:
    May 7, 2005
    You can probe again and then try to use a aerosol of carb cleaner to force it back further and out of the gallery but it has 90 degree turns where the dirt can hang up.
     
    Eric Bauer likes this.
  8. comnoz

    comnoz VIP MEMBER

    Joined:
    Dec 10, 2008
    Try a new set of plugs
     
    nortriubuell, 998cc and cash like this.
  9. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    My money's on a vacuum leak! (Since I don't have any money, this is not a concern - spent it all recently on a guitar.)

    Usual suspects are:

    1. Leak at the intake manifold(s) to carb(s) or intake manifolds to head.

    2. Balance hose between the carbs not sealing.
     
    Last edited: Jan 26, 2020
  10. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    Thank you - yes I'll try that for sure.
     
  11. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    How do you check your #2? There is an air bubble in the right hand side carb hose that never goes away. But there is no question something is wrong on the right side. Just the shear amount I can turn the air screw without much sensitivity leads me to something there. The other side (left) is very responsive to adjustment.
     
  12. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    Should I try and clean these first or just toss them? I don't have many tools here so just trying the low hanging fruit first.
     
  13. MexicoMike

    MexicoMike

    Joined:
    Jan 31, 2010
    The balance hose is located on the top of the intake manifolds. It has nothing to do with the fuel hoses. It's a hose that connects the two manifolds together via fittings at the top of each manifold. It forms an inverted "U" between the manifolds. You can't access it with the tank in place.

    Frankly, I'd suspect the carb/manifold/head fittings first - especially since you mention that one side is acting different than the other.
     
  14. MichaelB

    MichaelB VIP MEMBER

    Joined:
    Jan 14, 2004
    you can switch them and see if it goes to the other side.

    With it idling, spray some WD40 or equal around the intake manifolds, if idle increases, you have a leak.
     
  15. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    As for carb jet cleaning, best way to do it completely is to follow the tip in the Bushmans Guide linked earlier and drill out the blanked side of the mixture adjustment screw location. This gives you access to the passage that collects crud leading to no or low fuel into idle jet. Plug new hole by tapping and fitting a cut off spare mixture screw using locktite. Ive been able to push a wd40 straw up from where fuel enters carb body, turn 90 deg and further all the way to the newly drilled passage. This ensures no big blockages there.

    Your mechanic states new needles fitted, but not the type. Be sure they are correct for the carbs you have. 850 bikes should have 932 Amals and the stepped main jets. Running needles with the four bands and normally in the middle clip position. 105 or 106 needle jets and 260 mains is normal setup.
    What about float heights? Could a float be low or leaking leading to over rich on one side? New float valve needles?
     
  16. 998cc

    998cc VIP MEMBER

    Joined:
    Oct 1, 2018
    Definitely sounds like carburation as in posts above.

    But just in case, are the new sparkplugs correct for your Commando? Tappets/valves properly set? With the new plug wires, if suppression type, is there any carbon residue in the caps/on the tops of the ignition coils?

    Little things can have major impacts on proper running.

    Regards,

    ~998cc
     
  17. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    I guess I'll go buy a spark plug wrench and see if that tells me anything. This is much easier with tools ha ha
     
  18. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    Do the wires on the coil just pull off?
     
  19. alan hodge

    alan hodge

    Joined:
    Oct 10, 2017
    new needles but not new needle jets?
     
  20. Eric Bauer

    Eric Bauer

    Joined:
    Jan 10, 2020
    And is should say - it is after-firing in the exhaust, not actually backfiring.
     

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