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Cold start without choke in winter?

Discussion in 'Technical and Troubleshooting Torque' started by mugen86, Apr 24, 2008.

  1. When I was looking around for a bike I saw a few ads that claimed their bikes could cold start in winter without any choke.

    Does choke damage the engine?

    Is it possible for a bike to start when its 8 degrees? If so, what kind of condition must an engine be in for a bike to start without choke?

    Or is this just a sales puff?
  2. Choke richens up the fueling (explanation available if needed) to make cold starting easier. Once warm you don't need choke. If you run a warm bike with choke, you waste fuel, risk fouling the plugs and have a drop in performance.

    Not making a comment about the adds - not enough info.

    Cold starting is a topic all of it's own.

    Eidt: spleling
  3. if it's an FI bike you'd expect it to start without a manual choke.

    If its a carby bike then there is something wrong with the bike.
  4. Usually means it's running rich.
    The choke is there for a reason.

    And yes a bike will start at 8 degrees and much, much lower. Is possible for the carbs to freeze at really cold temperatures though.
  5. My bike starts easily without the choke. I'm pretty sure the emulsion tubes are due to be changed (they wear out in trx's, and i'm assuming in ducatis with the same carbs).
  6. Guess what: emulsion tubes and the carb slide needles wear out in every throttle slide operated carburettor.

    Emulsion tubes are also known as needle jets, and the needles in the slides are usually called jet needles!

    They wear in as little as 20,000 km and cause rich running to be noticed especially on light throttle in medium gears at 60kmh or similar, as the engine starts to 8 stroke or sound and feel a little as if the choke is on.

    As far as the OP's question goes:

    Being able to start without the choke in cold weather is a sign that the needle jets and jet needles need replacing. It is NOT a bonus or advantage of a bike, but just shows the seller's ignorance of mechanical things if they claim it as such. :)


    Trevor G
  7. You would know (or should know!) better than I at what temperature petrol freezes. It is way below the temperature that anyone can ride in.

    However, petrol engines can suffer from icing, where the water vapour in the air is frozen as it passes over the evaporating fuel. This is unusual for motorbikes as the carbs sit behind hot cylinders (usually). I have read of one recent Suzuki model which needed a mod to stop this happening, though.

    In cars special ducting around the exhaust manifold maintains the carb and the intake air at a warm-enough temperature to stop icing. However if this shrouding is removed (and not replaced) by lazy mechanics, or the hot air intake tubing is left off, then carb icing can occur at 10C, which is relatively warm.

    When it occurs the vehicle stops, and you will actually find ice built up on the carb venturi itself (and on the carb body.)


    Trevor G
  8. I never said the fuel would freeze, I said the carbs would freeze ie the carb icing you refer to.
    Very much a problem on a bike left outside all night if you try and start it when the temp is still well below zero - or at least it's a problem I've certainly had in the past.
  9. ahh I see :) thanks for the feedback guys.

    Some people selling 250s make it seem like it is an advantage to have a bike cold start without choke in Winter!

    Mmm I should ask a mechanic to replace the needles :cool: and get a quote... at least then he will assume I know something about the bike and not overcharge me!
  10. That's just a case of cold weather needing good choke conditions.

    Carb icing won't normally occur untill the engine has been running for some time at speed - 10 minutes or so on a highway. The ice forms inside the venturi where it blocks the jet(s).

    Ice on the outside after sitting all night won't matter much if the bike is in a good state of tune, with a good battery. Normally. ;-)


    Trevor G
  11. Had the carb icing problem, had carb heaters fitted under warranty.
  12. Hi Mugen,

    Not having a dig at you, but you seem to have a lot of questions regarding simple mechanical applications. That's cool, but have you thought of doing an introductory mechanical course or some spanner nights seeing as you've had no experience with vehicles before? :idea: