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  #1  
Old 22 Jul 2010
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Using the choke when starting up a motorcycle

Hey guys,

Any advice or tips on the best way to use the choke on a motorcycle? Turns out my bike has got one and the mechanic recommended I use it each time I start the bike up from cold.

But how much choke should I use? How long should I keep it open? Should I use it every time I start up the bike? And can mis-use/over-use of the choke wreck the bike??



All tips gratefully received, as ever!

Jeanie
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  #2  
Old 22 Jul 2010
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It's one of those things you get to know.....depends on the bike, temp. how long since it was last running, which way the winds blowing....from cold when its cold I use full choke/no throttle, if you ride off with the choke on its another thing to remember as you're riding. I've had bikes that didn't like full choke, some like a whiff of throttle, some have tested my patience and endurance trying to start them. One bloke I knew pushed a bike up and down a very big hill trying to start it, he failed, and on the last run down the hill let it free wheel and jumped of as it launched into the river!!!!! Patience and understanding.
If you leave the choke on too long the bike will stutter and hold back.
If you knock it off too soon the bike will die as you open the throttle, you'll get to know the spot on the road where the motor is warm and happy with no choke and knock it off at that spot automatically.
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Old 22 Jul 2010
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Your mechanic is right. When the engine is cold some of the fuel it gets from the carburettor condenses on the walls of the combustion chamber, so the mixture becomes too lean. The choke compensates for that. It will also open the throttle slightly, compensating for the fact that the engine needs more force to turn, because the oil is cold.

How much to use depends on your bike and the ambient temperature. Start off by putting it to full on. Once the engine is running smoothly you should ride off, don't warm up the engine standing still. You should be able to put the choke back fairly quickly. Experiment, you will soon find out what works best for you.

Yes, you can do damage if you leave the choke on for a very long time: too much petrol gets into the engine and washes off the oil film, so the piston will have insufficient lubrication. On many bikes you will notice that it won't run right, but on some you don't. You will have to remember it, just like you must remember to retract the side stand before riding off.

Don't use the choke if the engine is warm.
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Old 22 Jul 2010
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[quote=don't warm up the engine standing still. .[/quote]

Should I do star jumps while the bike warms up? Seriously though, Why not? Is there a mechanical reason for this...just curious.

I always use the choke (if engine is cold) and let the bike warm up to operating temperature before closing the choke and riding away. Only takes 3-4 minutes and it feels more sympathetic to the bike (it has feelings!)
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Old 22 Jul 2010
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I think it's because you're using fuel and going nowhere:- bad for the environment. However pulling out onto a main road and stalling could be very bad for your environment!
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Old 22 Jul 2010
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Quote:
Originally Posted by garmei View Post
I always use the choke (if engine is cold) and let the bike warm up to operating temperature before closing the choke and riding away. Only takes 3-4 minutes and it feels more sympathetic to the bike (it has feelings!)
No, bikes are machines, so they don't have feelings. But you do and you can feel, or rather hear, when the engine is running right (i.e. happily). After 4 mins. the engine is getting warm, but it's nowhere near "operating temperature". For that to happen the oil in the crankcase needs to be hot. Until that is the case, the engine is considered cold, although cylinder and piston are already hot. Now, running cold causes most of the engine wear. So, you want to run your engine cold for as little as possible. When you let the engine idle cold it takes the longest possible time to warm up, so you are maximising the wear on the engine. The recommended method is to let the engine idle until it runs "round", then ride away quietly and push the choke in as soon as possible. That way the engine warms up the quickest way possible.

Of course, if you were to use the maximum power when it's cold it would warm up even quicker, but then you will damage it, because the oil is cold and doesn't lubricate the parts very well.

Does this all make sense?
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Old 22 Jul 2010
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Good point, well made, I've obviously been sat idling too long!
Hi Ho Silver......
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Old 22 Jul 2010
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Most intersesting Beddhist. I getcha.

OK, 3-4 minutes was an understatement. I usually have a smoke/lock up shed/put hlmet on etc. Basically, the bike is pretty close to operating temp before I leave as it dles smoothly and revs right (feels right). Anyways...

What interests me is the idea that the best way to warm the engine up is to ride it (gently), this being the most efficient and quickest way, thereby minimising the amount of time the engine runs cold. I've never considered this before and it does make sense.

I always thought (maybe wrongly) that it was less damaging on the engine to let it warm up on the choke (@ ~3k rpm) and then at idle before starting off. My thinking is that the higher revs used when riding would be more damamging to a cold-ish engine even though the warm up period is a lot shorter than it would be if warming up stationary.

I use the choke to 'artificially' raise the rpm's to mimic actually running the bike to warm up, so maybe it's much of a muchness. Interesting tho..
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Old 22 Jul 2010
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RTFM.......every bike is different.
I have 2 BMW's (i'm not bragging, they're both old), one has a regular choke which alters the fuel air mix, the other does not alter this mix but instead is a fast idle. Both have the same lever that says CHOKE on it.
You have to know the machine that you're riding.
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Old 24 Jul 2010
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Engine warm-up and tackling slopes at the outset

Well I think I've got the hang of the choke now - it's all about listening to the bike, simple! More by trial and error than anything, I've got used to the different happy and sad sounds the bike makes with less or more choke (!) and adjusted my approach accordingly.

Still not sure how long to leave the engine running at a standstill before taking off though. In order to get out of my underground garage, I have to tackle two quite steep slopes right from the outset, which seems to demand a lot up front from the engine when it's still not fully warmed up. I gave it a lot of throttle this morning to get up the slopes (then stalled near the top of the second, which wasn't funny as I had the full weight of the bike to hold while I re-started the ignition!). So I'm thinking maybe I need to let the engine warm up for longer than if I was just taking off down a horizontal road...??

Jeanie
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Old 31 Jul 2010
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choke use depends on the bike. every ones different.
my XT600E needs full choke to start anytime unless its already warmed up, start and then immediately put on half choke till it'll idle without. you can ride with the choke out ok but idling will be very high. being aircooled you can ride straight from starting no problems, in fact you shouldnt leave an aircooled bike idling for too long because theres no cooling. i have been stood chatting with the choke out before and turned round to see the downpipes glowing red hot!

a watercooled bike is the other way, it takes longer to get up to temperature and you should let them warm up a little even if its only for a couple of minutes while you get your helmet and gloves on.

neither style of bike should have its neck wrung till its warmed up properly of course, but gentle normal riding is fine.

even my varadero has a "choke" (its not a proper choke, being fuel injected it doesnt need one, its just an air valve in the inlet) for a little help on really cold days. otherwise the ECU sorts the fueling out for you.
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Old 31 Jul 2010
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If you want a really dumbed down expanation for a choke:

Your engine burns a mixture of air and petrol..

When the engine is cold, the engine likes more petrol in the mixture than usual.

The choke usually "chokes" the air supply into the engine so it gets more petrol than usual. Hence it's name.


You should start the bike from cold with half or full choke depending on how cold it is. After 30 seconds is usually enough for most bikes. Especially a small thumper.

Just reduce the choke slowly. If it wont idle smoothly (sounds like an asthmatic pensioner) then it probably wants the choke on a bit longer.


NEVER run the choke longer than you need to. It will soot up your spark plug and all that extra petrol will increase wear on the engine (it thins the oil in the combustion chamber)
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Old 1 Aug 2010
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Thanks for your advice guys.

Still experimenting with the choke, as I don't think I've quite sussed it yet. The Marauder seems to need a LOT longer than 30 seconds of choke - the engine just splutters and dies if I try and reduce it even after a few minutes. I usually start it with half choke as opposed to full choke - at full choke, it very quickly revs far too high, prompting me to reduce it to halfway where it then sits and idles nicely as it warms up. After about five minutes, though, still unable to get the engine to idle in neutral without any choke at all, I've been riding off with the choke still partially applied, then shutting it off after a few minutes on the road. Not sure if this is good for the bike but it seems to work...

Jeanie
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Old 1 Aug 2010
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Quote:
Originally Posted by jeanied1 View Post
Well

Still not sure how long to leave the engine running at a standstill before taking off though. In order to get out of my underground garage, I have to tackle two quite steep slopes right from the outset, which seems to demand a lot up front from the engine when it's still not fully warmed up. .... maybe I need to let the engine warm up for longer than if I was just taking off down a horizontal road...??
IMHO don't get too tied up in this. The choke/enricher/increased idle device* is just there to get the thing moving. If the bike is warm enough to go where you need with the cold start device on, then go. If it stalled, chances are it would have been fine with a bite more throttle or waiting 30-seconds, it doesn't really matter which. The internet theorists are going to howl about wearing the engine out faster, but in the scheme of things you'll be knocking tens of miles off the life of components that should be lasting hundreds of thousands. I wouldn't idle a bike in an eclosed garage for long, think of all the soot and rubbish you are breathing in.

* the last bike I saw with a choke (restricted air supply) was a Dnepr, say no more, this is 1930's technology! Most carbed bikes have an enricher circuit. The cable goes to a plunger on the side. Pull the plunger up and there is an extra passageway to let more petrol into the engine. The bike runs richer, so uses more fuel and will eventually foul it's plugs. (If you ever own a Guzzi, the O-rings swell, the dealers tune the bike to run on constant choke and the *****y thing does 15 mpg and fouls the plugs every 50 miles ). When you clean the bike, have a feel of the choke cable operation, you should feel it close. FI bikes just have a switch that tells the computer to let it idle faster to avoid stalling. The fact that the Berlin-Munich loons decided to put said switch on the end of a steel cable is beyond me, but we are talking about the blokes who designed an indicator switch set that needs three thumbs!

Andy
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Old 1 Aug 2010
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Originally Posted by Threewheelbonnie View Post
* the last bike I saw with a choke (restricted air supply) was a Dnepr, say no more, this is 1930's technology! Most carbed bikes have an enricher circuit.
Andy
True.. But I was trying to put it in a way a novice would understand... The theory is the same.

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