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Warm Start Troubles

Discussion in 'Norton Commando Motorcycles (Classic)' started by Tornado, Jul 1, 2018.

  1. Steves

    Steves

    Joined:
    Oct 16, 2016
    Your carb fastners are too tight. You need to use spring washers and just nip up the 2BA’s. To tight and you distort the carb body and the slides will stick.
     
  2. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    Your carb should not be getting that hot, I think you said in an earlier post you had a heat insulating gasket fitted?
    Do you have insulating washers on the carb mounting nuts? Worth putting some in if you haven't
    Cheers
     
  3. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Bike did come with phenolic gaskets which I have refitted btwn mani and head (2 into 1 mani...so perhaps greater heat transfer that two separate mani's). No washers under mani to carb nuts...will see what I can do there.
    However, even the air filter Ham-Can seems quite warm...and this should be safe from conductive heating...only radiant from the head should impact it...and also the carb body.
     
  4. RobinKent

    RobinKent

    Joined:
    Jan 31, 2010
    Radiant heat from the cylinders too but if you have the phenolic spacers fitted treat the heat as normal for now. Sounds like your problem was carb settings. When hot make sure throttle is open 1/8 + to start. Pilot jet is an idle circuit not a starting circuit.

    So. Now you understand why we love Commandos so much:

    Torque + Handling + mental challenge.
     
    Tornado likes this.
  5. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    I too run with single carb it a Mikuni but similar mounting as what you have , never have had a hot to the touch carb .... if you have heat insulating gasket mounted , I wonder where all excess heat is coming from .....
    Craig
     
  6. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Doesn't the Mikuni have a big rubber flange to mate the circular forward end of carb to flat rearward side of manifold? That would do a much better insulating job that the tiny o-ring of the Amal. Also note, the carb was cold right after riding....still with bowl full of fuel evaporating away taking heat with it. I shut off the taps while hanging around...so once residual fuel evap'd away, carb has no more coolant and begins the bake cycle. Leaving the taps open should prevent heat up, but then it would be constantly drawing fuel in to feed the evaporation rate.
     
  7. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    Yes I suspect you are correct .... for no reason I had thought your single Amal would be connected in similar fashion as my single carb ... wonder if you could go that route and mount as if it a Mikuni ....
     
  8. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Amal is flanged on the front side towards the mani...and the milled slot for the o-ring means the two opposed flange surfaces are only separated by one or two MM tops...a thick-walled/rubber/phenolic/fiberous gasket could be used there instead of the o-ring to give a little more spacing and better insulating and added benefit of better resistence to bending on the carb flange bolt hole "ears". I was going to order up new phenolics...might just get some extra and try stacking them mani to head and mani to carb as well.....
     
  9. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Japanese bikes use rubber mounts for the carbs - they insulate from both heat and vibration. I have rubber mounts on my Seeley which I bought years ago from Mick Hemmings. There are two types of rubber - one for petrol, the other for methanol. If you use the wrong type, you can get cracking. With a standard Commando you might not have enough room to use them - however Mick would know.
     
  10. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    Yes , if you went that way , you would have some work to do around air filter ... still with a rubber boot between carb and intake , you would have peace of mind ...
     
  11. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    Just did some looking around , looks like you have some options to get rubber manifold adapter, appears that Amal and Mikuni units
    are available ....
     
  12. baz

    baz VIP MEMBER

    Joined:
    May 26, 2010
    30 odd Years ago I ran my mk2a with a Norton atlas manifold and a single mk1 concentric
    I cut the mounting flange off the manifold and re welded it to suit the commando motor leaning forward
    I did this out of an act of sheer impovorishness it ran spot on in a dreary sort of single carb way but I don't ever remember the carb being too hot to touch !!
     
  13. RobinKent

    RobinKent

    Joined:
    Jan 31, 2010
    When running the carb is cooled by the huge flow of air through it. When you idle or ride slowly in town then stop it is inches from an extremely hot air cooled engine and heats up, as does your air filter front plate, legs etc. Stop the airflow over the head and heat rises instantly. To 375F or more.

    Try "Temperature and Lubrication of the Norton Motorcycle Engine".

    https://www.google.co.uk/url?sa=t&s...FjAAegQIARAB&usg=AOvVaw2GGtOUzCt22Je7EzK4qzSN


    Its how others mount them. Its unlikely its a problem.
     
  14. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    The oil testing read was good. Thx.

    While airflow must have cooling effect on the carb...I'm very sure having fuel evaporating inside the bowl has a more significant cooling effect. When I found the throttle getting stuck at wide open with the hot to touch carb, I opened the fuel taps, and within only 5 or 10 seconds, the throttle slide was no longer sticking at wide open and the carb body was no longer too hot to touch comfortably....and actually at/below ambient within a minute. Evaporation, liquid to gas transition, takes heat energy...which is being absorbed from the metal of the carb body. Works in an Air Conditioner exactly the same way.
     
  15. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    Yup , back in the day working for hot air balloon fools .... end of day ritual was cooling beer with propane from the 90 pounders we flew with .... had to be careful not to burst the warm bottles .... back to your issue , you need insulator between carb and heat source , right , you have options .... so onward and upward eh ?
    Craig
     
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  16. RobinKent

    RobinKent

    Joined:
    Jan 31, 2010
    Absolutely but I wanted to keep the post bite sized on quite why the carb can get very hot without anything being 'wrong' .

    If it gets that hot and then has fuel added it will cool rapidly for those reasons.

    Liquid to gas state change also increases volume by what? 22 times rings a distant bell. If the carb and manifold were always running way too hot, larger than expected amounts of fuel would change state, charge density would be far lower and we'd be way down on horses which doesn't sound the case. Sounds like phenolic washers are doing the job.

    Sticking slide needs investigating in any case!
     
  17. RobinKent

    RobinKent

    Joined:
    Jan 31, 2010
    You learn something new every day.

    I've always assumed evaporation is very low when you pull up because the main jet and pilot jet are so small and if I drain the carbs there is always plenty of fuel to come out (UK temperate climate). On the other hand, my very lovely girlfriend has asked about the smell in the garage after a run.

    I said I always smell which she easily accepted but I ride the last half mile or so at slow town speed, leave the bike idling as I negotiate the gate keypad and later as I walk around to open the garage from inside before shut down and fuel off. Takes 3-4 minutes. The oil temperature article suggests that's pretty much the best way to reach max engine degrees and by extension carb heat, evaporation and... smell!

    Better change my ways!

    Rob
     
  18. franko

    franko VIP MEMBER

    Joined:
    Dec 29, 2013
    Have small cracks developed in the rubber connector of the carb to manifold?
     
  19. Craig

    Craig VIP MEMBER

    Joined:
    Dec 20, 2005
    That one issue Franco , from what I can figure he has no rubber type adapter , just o-ring between carb and intake manifold , not sure what he has between manifold and intake ...
    Craig
     
  20. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    The Amal single setup has an o-ring sitting in a groove milled into the carb body flange. This compresses up against the 2-1 manifold flange flat surface. The mani to cylinder head intake ports have a phenolic gasket around each port. No rubber boot involved forward side of carb...just the air filter side has the boot.
     
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