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Starting a carby bike Help with (do's and don's)

Discussion in 'Bling and Appearance' started by hyper24, Feb 6, 2006.

  1. Reading another thread, the guy said how he realized giving a carbie bike throttle to start is bad.

    Whys this?

    Should a bike ONLY need the choke pulled and button pressed, if it needs reving something is wrong?

    I thought the choke gives it more fuel, so choke and reving would be the same thing.
  2. The throttle gives the engine more air and fuel, the choke just gives it more fuel (richer mixture). When an engine is cold, the fuel can have trouble vaporising so the choke puts more in (which is why you turn it off once the engine starts to warm up, otherwise it gets too rich and you can foul plugs etc).

    The choke usually also operates a jigger (can't remember the name) which prevents the throttle from completely closing, but you have to rev it once with the choke on for the throttle to open and stay open.

    So, as long as it's not flooded and it's a cold day, turn choke on, give it a rev, then start it.

  3. Depends on the carby as to whether a fast idle stop is fitted.

    A lot of carbies rely on a piston/plunger setup to introduce fuel via what's called the pilot jet or circuit to richen the fuel air mixture. Others have a butterfly that covers the mouth of the carby, which more or less does the same thing. The choke butterfly may have a link connecting it to the throttle to partially open it. or it may have an idle stop that delatches once the choke is pushed back in, turned off or whatever.

    In general operation, though, just give it full choke, no throttle and crank/kick start away. Once the engine's fired, back the choke off til it looks like stalling, then hold it there. There's no need to have full choke for any periods longer than necessary. Particularly if you're in your garage or under a carport that has a door going into the house. Tends to smell a bit.

    Idle for a minute or two while putting on helmet, gloves, etc. As soon as you move off, turn off the choke. It does nothing for the engine except to make it run richer, which can cause plug fouling and excessive fuel use.
  4. When I first started riding, I often forget to turn the choke off... I find that the bike tend to stall when I pull to a stop. As soon as I turn the choke off, the bike runs like normal.
  5. I usually only put choke on partially, then press the starter - no throttle.

    If the bike doesn't start within the first couple of cranks, stop and give it a touch more choke.

    It generally starts fine then.

    (BTW you quickly get used to how much choke your bike needs to start in normal conditions. Sometimes it needs a little more if it's very cold, and a little less if it's a warm day).

    Allow it to idle with choke partially on while putting on helmet gloves etc, then ride away. Disengage choke when riding off, and ride easy (no hard revving) for the first few kays...

    The reason I don't engage the choke fully before starting it first off is that if you do that the engine usually wants to rev it's tits off until you adjust the choke to a slower idle.

    The bike revving it's tits off from cold when it is first started is a bad thing, 'cause the oil is all sitting in the sump, and the engine is running dry when the tacho reaches skyward until the oil gets pumped up around the engine.

    Much better to only have enough choke to get it started IMHO. That way the idle is slow to beginning with and allows the engine to get oil circulating without being revved out dry.

    That's what I do anyway ;)
  6. All bikes are different, older, newer, dirty plugs, poor compression etc etc etc
    My old beast needs no throttle at all, some bikes need to have the throttle slightly opened to kick (my across needed that), some require a throttle "twist" to set a fast idle postion before cranking..... wotever.

    Only way you'll damage the engine is by really revving it as it starts (ie as soon as it kicks), you're thrashing the pistons/valves/cams with bugger all oil getting pumped around. Not good for ANY engine, carby or EFI

    Do whatever it takes to make it run, once started give it only enough choke so that it'll run smoothly, and reduce choke (progressively) as soon as you can. Let it warm up as you put your gear on.

    I give it the occasional "tweak" on the throttle to see if it has a flat spot, sure sign it isn't ready to reduce the choke.