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Idle when hot.

Discussion in 'Norton Commando Motorcycles (Classic)' started by htown16, Mar 16, 2019.

  1. htown16

    htown16 VIP MEMBER

    Joined:
    Apr 29, 2009
    Got my 74 850 back on the road after complete rebuild. About 500 miles on it. Seems to run just a little hot which I'm attributing to the engine still being a bit tite. Timing is spot on. Pulls really good and idles okay at first. If I shut the bike off after a good run say to get gas, I have to ticke the carbs to get it going again. Also, it won't hardly idle after that. Idle speed just drops til it stalls like it's starving for gas. I do have the tufnol spacers between the manifold and head. Any ideas.
     
  2. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    My 850 single carb got too hot to touch after fuel stops etc. This seemed more than enough to vaporize fuel in the bowl. Even made the throttle slide jam at wide open position when I checked it before a startup. I put phenolic spacers at manifold to head and at carb to manifold. Completely solved it.
     
  3. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    Does it stall when idling with no throttle? Or does it sputter out just off idle? If you have to tickle to get it started when warm, that would suggest a lean condition, either in the jetting or due to an air leak somewhere along the intake. Try closing the choke next time to see if that clears it up. If it does, I'd then check/clean the pilots, confirm floats at correct height, and if that's good spray some carb cleaner around the inlet manifold while it's running to check for an air leak.
     
  4. htown16

    htown16 VIP MEMBER

    Joined:
    Apr 29, 2009
    Stalls when idling. Idles fine until after it's been shut off and restarted or ridden really slowly like coming into my neighborhood. I'll check for air leaks. New Premiers with 19 idle jets, set at one turn out. Checked the fuel level with u-tube.
     
  5. ashman

    ashman

    Joined:
    Jul 11, 2010
    Normaly when running hot idle will idle higher when in traffic etc, if it stalls when sitting still you could have your idle down to low as well running to lean or air leak, and if you have to tickle it when the motor is hot its is running to hot, when I first brought my Norton new in traffic the idle would rise when hot one of the reasons I put a oil cooler on my Norton at a early age of its life.
    Another reason running hot is if your rebuild had a rebore and your bore to final hone is a bit tight but, its proberly running too lean, but running in your rebuild the oil might be a bit thin or light for runin purpose after first oil change put some decent oil in it if you think its not running lean.

    Ashley
     
  6. htown16

    htown16 VIP MEMBER

    Joined:
    Apr 29, 2009
    Tornado mentioned an additional spacer between carb and manifold. Anyone done this on Amals. The K+N airfilter is a tite fit already.
     
  7. acadian

    acadian VIP MEMBER

    Joined:
    Mar 5, 2010
    That's the 1/4" phenolic spacer that insulates heat, it's the only spacer that should be in the inlet. Your first post mentioned that you already have these installed.
     
  8. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Though the parts diagrams only show phenolic insulators between manifold and head, I can see no downside to placing an additional one carb to mani side. I've used light amounts of Permatex Grey flange sealant on sealing surfaces....so air leaks are not an issue. As I mentioned. my carb bowl was too hot to touch 10-15 min after shutdown before I did this and starting up following brief shutdowns/fuel ups usually needed tickling as OP described. My carb bowl no longer gets hot at all. This might have been a problem with the 2 into 1 manifold and not a common issue on two carb setups...but it's easy and worth checking the carb temp minutes after shutdown IMHO.
     
  9. RoadScholar

    RoadScholar VIP MEMBER

    Joined:
    Dec 28, 2008
    You have a fresh engine, they need to seat rings and seal valves; such conditions make stable tuning difficult. Have to been judicious about re-torqueing engine fasteners and monitoring valve lash? If the single carb (any carb or carbs) has been stored with last years fuel your idle circuit may be constricted. Back in '72 I replaced a head gasket and was in a hurry to get down the road and did not revisit the head torque as I should have; I looked down at the engine when at a stop light and saw the fuel line almost melted through, the carbs were too hot to touch and I was very lucky that the bike didn't light up...

    Rocky Point Cycle has sold 100s of Mikuni kits, with the exception of a small number of altitude jetting corrections none of the kits required any type of heat insulators between the head and manifold.

    My guess, without seeing the "patient" is that your jetting is possibly lean, your head needs to be re-torqued, your valves should be checked, that your timing rechecked at 3500 RPM, or until it show no further advance and that your throttle cable has some slack when the throttle is closed. If you have the OE AAU make sure that it isn't worn and the springs are returning the points cam to its idle stop consistently.
     
  10. htown16

    htown16 VIP MEMBER

    Joined:
    Apr 29, 2009
    Pulled plugs and mixture looks right on the money. NGK BP8's. Carbon ring up to the first thread turn. These are Premier carbs and have the removable idle jets. Just replaced the 17's with 19's a little while back. Air screw is one turn out. In theroy it shouldn't be lean on idle. Pazon EI timing set about a hundred miles ago. It will start up from cold usually on one or two kicks. No indication in mid range or WOT of a problem. I would think an air leak would be problem all the time. What gets me is that when the engine is really warmed up after a good run the idle starts stalling.
     
  11. jimbo

    jimbo VIP MEMBER

    Joined:
    Sep 25, 2004
    Defective coils when hot causing a weak spark at a low electrical energies ? Hard to detect except by swapping out parts.
     
  12. Bernhard

    Bernhard

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    Apr 20, 2011
    Only one turn out? - is that right?
     
  13. jimbo

    jimbo VIP MEMBER

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    Sep 25, 2004
    usually I set them at 1 1/2 turns out to begin but who knows with those new and improved carbs
     
  14. Bernhard

    Bernhard

    Joined:
    Apr 20, 2011
    I suggest you borrow or buy a second-hand Colour tune - and use it on a warm engine in the dark -you will get your carb mixture spot on then- if is just one tenth of a turn out at present you WILL notice the difference after-don't ask me how I know.

    Also look for missed sparks that may show up when idling –you have some electrical issues
     
  15. jimbo

    jimbo VIP MEMBER

    Joined:
    Sep 25, 2004
    I have a Color tune kit I could sell for $50 pm me
     
  16. Craig

    Craig VIP MEMBER

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    Dec 20, 2005
    I thought most carb brands were 1 1/2 turns out as a starting point ?
     
  17. Adam M

    Adam M

    Joined:
    Mar 16, 2019
    Hi Htown, perhaps it could be too rich when hot on idle / low revs ?
    Had this problem with BSA and it's choke slowly moving position to partially closed during riding and engine suddenly stalling during idle.
    Perhaps 1 rev out is too rich on hot engine.
     
  18. ashman

    ashman

    Joined:
    Jul 11, 2010
    1 1/2 turns is just a guide when putting new carbies on, or after doing anywork on your carbies, I have tuned my Norton the old way by killing one cyclinder and tune the carbie that is on the running side once its all set kill it and do the other side, has worked very well for me doing it this way for over 40 years on twin carb bikes, some carbs will be different in how far out or in the adjuster screw will be, you will have to adjust the idle screw a bit higher idle to do this, adjust the air screw in and out till its sweet spot and then do the other side, even needles can be in different positions on each carbie, remember you are turning each cyclinder, unless you have only a single carbie.

    Ashley
     
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