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Posted by Gerrit on August 9, 2007, 6:07 pm
Why is it harder to start a cold engine vs starting an already warmed-
up engine, special on older bikes. Based on the three primary
factors: Spark , Fuel/Air mix and Compression. What improve so much?
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Posted by Albrecht via MotorcycleKB.com on August 9, 2007, 6:18 pm
Gerrit wrote:
>Why is it harder to start a cold engine vs starting an already warmed-
>up engine, special on older bikes. Based on the three primary
>factors: Spark , Fuel/Air mix and Compression. What improve so much?
The distribution of burnable fuel/air mixture in the combustion chamber is
rather random. In order to ignite, the cold engine needs a richer mixture to
improve the odds that there will be burnable molecules in the spark gap as
current jumps to the ground electrode.
Once the engine is running, a leaner mixture can be used.
Older Japanese motorcycles with ignition points and low voltage coils were
harder to start than modern bikes with electronic igniton. They either needed
more voltage so the spark plugs could be gapped wider, or they needed a
rather rich mixture. This resulted in spark plug fouling and the need to
clean the plugs every three or four thousand miles.
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Message posted via http://www.motorcyclekb.com
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Posted by on August 9, 2007, 8:50 pm
wrote:
>Gerrit wrote:
>>Why is it harder to start a cold engine vs starting an already warmed-
>>up engine, special on older bikes. Based on the three primary
>>factors: Spark , Fuel/Air mix and Compression. What improve so much?
>The distribution of burnable fuel/air mixture in the combustion chamber is
>rather random. In order to ignite, the cold engine needs a richer mixture to
>improve the odds that there will be burnable molecules in the spark gap as
>current jumps to the ground electrode.
>Once the engine is running, a leaner mixture can be used.
>Older Japanese motorcycles with ignition points and low voltage coils were
>harder to start than modern bikes with electronic igniton. They either needed
>more voltage so the spark plugs could be gapped wider, or they needed a
>rather rich mixture. This resulted in spark plug fouling and the need to
>clean the plugs every three or four thousand miles.
maybe on 2 srokes but none of my 4's, among whic are xs-654'd-750's-1100's and
many sr 500's. the plugs on those stayed fine. i do cheat, though, i keep them
tuned, adjusted and started at least once every 2 weeks.
many yamays have weak sparks, but hotter plugs help a lot.
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Posted by Albrecht via MotorcycleKB.com on August 10, 2007, 1:56 am
Albrecht wrote:
>The distribution of burnable fuel/air mixture in the combustion chamber is
>rather random. In order to ignite, the cold engine needs a richer mixture to
>improve the odds that there will be burnable molecules in the spark gap as
>current jumps to the ground electrode.
When the engine is warm, the gasoline atomizes better, so the engine starts
on a leaner mixture.
--
Message posted via MotorcycleKB.com
http://www.motorcyclekb.com/Uwe/Forums.aspx/yamaha/200708/1
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Posted by Gerrit on August 10, 2007, 6:00 pm
wrote:
> Albrecht wrote:
> >The distribution of burnable fuel/air mixture in the combustion chamber is
> >rather random. In order to ignite, the cold engine needs a richer mixture to
> >improve the odds that there will be burnable molecules in the spark gap as
> >current jumps to the ground electrode.
> When the engine is warm, the gasoline atomizes better, so the engine starts
> on a leaner mixture.
> --
> Message posted via
MotorcycleKB.comhttp://www.motorcyclekb.com/Uwe/Forums.aspx/yamaha/200708/1
Does the Compression play a roll? The manual (xt550 '83) say it should
be 156psi, I only get about 130psi (wet/dry). What is the tolerance
on that. My tester can't be 100%, because it works with a rubber end
on the sparkplug hole (at a place where you can't see nothing!) How
much compression do I loose with the automatic compression release,
will it help to disconnect that?
How do I know if I have a low voltage coil?
Where do you kick from? TDC, pre-, post?
Thanks for all the help!
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>up engine, special on older bikes. Based on the three primary
>factors: Spark , Fuel/Air mix and Compression. What improve so much?