1. This site uses cookies. By continuing to use this site, you are agreeing to our use of cookies. Learn More.

Warm Start Troubles

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

  1. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    850 MKII with single Amal 932 carb. Only been running bike a few weeks, so very little experience with it/any carb bike.

    Was going OK a few days ago.1-2 kicks warm or cold after tickle and choke if cold. Last couple of days, seems to have trouble idling immediately after kicking...will drop below 750 rpm and dies unless I hold throttle open. Has happened like this the last three fuel stops and even after 30-40 min coffee stops. Once running for 5+ min, it's happy at 1000-1200 idle, stop go traffic...no stalls at all.

    Bike has EI (Vape Wassell...which apparently is similar to the Boyers).
    Bike does pop a lot when coming off throttle at speed...normal?

    What should I be checking for, Too much fuel or too little after start up?
     
    Tags:
  2. Mr. Rick

    Mr. Rick VIP MEMBER

    Joined:
    Feb 6, 2009
    I personally don't even pay much attention to what the bike is doing until after it has warmed up, even just a little.
    I use that little throttle tension bolt to keep the idle up enough to prevent stalling at first start, make sure the choke is all the way off.
    But I'm certainly not waiting 5 minutes, more like 1 if it's dead cold. And I always rev it up to 2 or 2.5 K before letting it back down, telling myself I'm helping the cam get lubed.
    I can't really offer much advice about yours, since I run twin carbs.
    Do the plugs tell you anything?
     
  3. Steves

    Steves

    Joined:
    Oct 16, 2016
    Turn the air screw in 1/4 to 1/2 a turn. This will make pilot circuit richer. Adjust idle with slide adjuster. Popping and banging is air leak in exhaust or weak mixture. Should idle at circa 900 rpm when warm. With choke it should idle from cold. Might be worth checking choke cables etc. Also as an experiment when bike is popping and banging you could apply choke and see if it makes a difference. You could also try starting bike with fuel off no tickle no choke after your coffee break, just remember to turn fuel on if it starts.
     
  4. maylar

    maylar

    Joined:
    May 13, 2007
    Popping under decel is a classic symptom of a clogged idle passage in the carb. Especially if the bike had been running well previously. A leaking exhaust will do that too but that doesn't usually affect starting.
     
  5. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Is the fuel tank clean inside?

    Glen
     
  6. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Thanks, got some things to try now.
    Re tank inners...it could be cleaned up, de-rusted with the acid /Evapo-Rust treatment. I do have filters on the fuel lines though.
     
  7. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    Try the next range hotter spark plugs, you might have a plug fuelling problem
     
  8. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Assuming u meant fouling, I just pulled plugs and found then light grey/whitish tip, and light black ceramic/body. Certainly not sooted. Gave them a brass brush cleanup and confirmed gap at. 023".
    Also ran the #78 bit thru pilot.
    Gonna test ride soon.
     
  9. Steves

    Steves

    Joined:
    Oct 16, 2016
    Changing plugs is something to do when you are confident everything else has been done and set correct. If you are doing a strip and clean, change for sure needle jet with new if you don’t know provenance of old one. Set idle (1200) on hot engine with slide screw, then airscrew so it runs faster, then slide screw back to 1000/1200, then airscrew so it runs faster (small adjustments) slide screw idle to 900/1000 then adjust airscrew about 1/8 to 1/4 rich. Adjust richer if it pops. It should be straight forward with one carb, it’s a pain with two but quite satisfying, at least to me :)
    Float height is another consideration but assuming it’s in the ball park you should be good. Very rough guide (I think!) if the fuel is on and has stopped filling float bowl and you time about 2-3 seconds from pushing tickle to over flow fuel then it’s good.
     
  10. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    So cleaning jet, gapping plugs does not seem to have cure the warm start problems. Had no stalls once up and running but made three stops, one for fuel and each time starting/keeping it running more than 10 seconds was quite tough...needed throttle held open for 1-3 minutes.
    Played a bit with idle mix screw but not as systematic as Steves described above. Not much change.
    Could this be fuel starvation from a stuffed up cap vent? Thinking here tank pressure lowering when shutdown, creating some suction preventing correct bowl flow until things heat up a little more.
     
  11. Mr. Rick

    Mr. Rick VIP MEMBER

    Joined:
    Feb 6, 2009
  12. Steves

    Steves

    Joined:
    Oct 16, 2016
    Fuel evaporates out of the float bowl. If you have clear fuel lines you should see fuel flow when petcocks opened. I would open fuel cap before starting if you think it might be a vent problem. Have you checked for air leaks between carb and cylinder head?
     
  13. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    I did try to start once yesterday after popping cap open. No difference really...and doesn't really explain why hard to start immediately after fuel fill up. I was wondering if there is guidance on how to inspect or clean the fuel cap as I'm not sure where it vents from.
    I did have concern for intake leaks a month ago, Found a gouge in the manifold to carb mating surface. Glassed the manifold and filled gouge with epoxy and faired on glass. Starts/runs were not bad before/after that work...I was trying to solve a stumble /stall just off idle...sorted with fresh needle and jet.
    Float was set to prescribed level as per Bushman guide...2 mm below bowl lip. And recall bike was starting, running well just 10 days back. The harder starting has been sneaking up, seems to be getting
    worse...I now expect hard starts
    instead of one kick wonders.
     
  14. L.A.B.

    L.A.B. Moderator VIP MEMBER

    Joined:
    Nov 20, 2004
    There should be a small breather hole in the circular 'rib' of the lower cap plate......

    [​IMG]

    ....that connects with another hole in the upper cap plate via the gallery formed by the two plates.
    (Upper plate view)
    [​IMG]

    Your plate assembly is likely to be riveted to the actual cap instead of fixed by a screw.
     
    Last edited: Jul 3, 2018
    Tornado likes this.
  15. tomspro

    tomspro VIP MEMBER

    Joined:
    Jan 25, 2014
    I once got a bad tank of gas (e-free) that caused similar symptoms.
     
  16. cash

    cash

    Joined:
    Nov 10, 2006
    A long shot but is it flooding? Perhaps the float valve worn and passing just enough fuel not to matter when the tank is low and when the bike is motoring, but when filled the extra head is enough.

    Try switching off the fuel before you stop and don't turn it back on until it starts.
    Dave
     
  17. acotrel

    acotrel

    Joined:
    Jun 30, 2012
    When you kick the motor over when it is hot, if you have good compression, you should be able to feel it. If you have flooding, it is usually easier to turn the motor over with the kick start lever, than when you have the correct mixture. The tank breather might be blocked and causing a vacuum in the tank. If the motor starts then stops after running for a while, that might be your problem. But to me, it sounds like an electrical problem due to heat - might be the coil or a condenser.
     
  18. Steves

    Steves

    Joined:
    Oct 16, 2016
    Stumble stall off idle you mention to which you applied new needle jet and needle which is good, but have you tried raising needles a notch? There is an over lap between circuits, (pilot, needle, main). I realise that when something works and then doesn’t for no apparent reason it can be frustrating. It could be as previous poster said something else. There is much to the adage 90% of fuel problems are electrical and visa versa. A simple test is after a run feel the heat at the end of each silencer, is it roughly the same or is there a marked difference. A temp sensor is good, if you use your hand take care!!! It could be a knackered coil, have they been pinched in the clamps?
     
  19. Tornado

    Tornado VIP MEMBER

    Joined:
    Dec 5, 2017
    Well doing lots of riding today...highway stuff out to meet up with Worntorn. Today, seems my hot starts are pretty good...a few kicks at most. I did note a few times the failed kicks seemed too easy at turn over...flooding might be true.
    This is all since some idle mix adjustments made later yesterday. Also tightening up of header rosettes. But after a 20 mile ride, we stopped to chat. I noted my carb was cool to touch. After 20+ min of jaw waging, carb was too hot to touch...just happened to twiddle full throttle and stunned to have it jam wide open. A very light tap top of carb and it snapped down.
    Repeated this several times. Opened taps to let fuel in, cool it down solved the jams. Not sure if this at all related to hit starting issues.. but got me a bit freaked out now.
     
  20. worntorn

    worntorn

    Joined:
    Dec 22, 2006
    Well you made it home ok then!

    Just use a bit of 320 Emery on the shiny spot(s) of the slide.
    Its likely up near the top.
    Its a fairly common occurrence , but easy to fix.

    Glen
     
    Tornado likes this.

Share This Page

Loading...