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Engine misfire

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Ielgie
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Engine misfire

Post by Ielgie on Thu 14 Sep 2017, 10:12 pm

I have just bought a low mileage CB500 (14000, baked up with old mots). It is a 1994 model. I bought it for use to and from work, and occasionally use at work, I am a motorcycle instructor. It has been regularly serviced, the last time in April when it was mot'd. It has done very little miles since.
It has a misfire between about 4500 and 6500 revs. 
It starts easily without the use of the choke.
I rode it home today in the rain and it seemed worse, although it still pulls very well and is great fun to ride.
Can anyone help with likely causes. 
Thanks
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Beresford
the 900
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Location : not that far from Kirkistown

Re: Engine misfire

Post by Beresford on Thu 14 Sep 2017, 10:25 pm

I'd check the basics, as "service" wasn't done by yourself, I assume. So as the bike is 23 years old, have a look at the carb rubbers which may be perished, and air filter which may not have been replaced or may even be missing.
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Ielgie
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Re: Engine misfire

Post by Ielgie on Thu 14 Sep 2017, 10:28 pm

I have checked the air filter and it looks brand new which led me to believe the rest would be ok. I intend to change plugs and oil anyway and then I know they have been done. Any other advice whilst I have it apart.
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Jameshambleton
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Location : Bedale, North Yorkshire

Re: Engine misfire

Post by Jameshambleton on Fri 15 Sep 2017, 8:29 am

I'd suspect it'll be your plug caps on the end of your ht leads. Make sure that they are fully clipped onto your sparkplugs and need to have a reasonable amount of force to pull them off. 
or 
it's the carb diaphragms that's causing your issue, maybe worth checking if you've got any restictor washers between the carbs and inlet rubbers on the back of the engine
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eternally_troubled
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Location : 'ere be fens. (near Cambridge)

Re: Engine misfire

Post by eternally_troubled on Fri 15 Sep 2017, 7:45 pm

If you decide to take it apart you might as well balance the carbs while you are there Smile More seriously, I suspect it is worth looking at your HT leads and coils like James suggests - on my bike (which is 3 years younger than yours) the HT leads and coils are certainly 'on the way' to failing.
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Jameshambleton
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Location : Bedale, North Yorkshire

Re: Engine misfire

Post by Jameshambleton on Fri 15 Sep 2017, 8:44 pm

eternally_troubled wrote:on my bike (which is 3 years younger than yours) the HT leads and coils are certainly 'on the way' to failing.

My coils have had it at about 55k miles because of the spade connections on the coils them selves. @Andyc's 929 blade stick on coils are working well
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eternally_troubled
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Re: Engine misfire

Post by eternally_troubled on Tue 19 Sep 2017, 8:59 pm

Jameshambleton wrote:
eternally_troubled wrote:on my bike (which is 3 years younger than yours) the HT leads and coils are certainly 'on the way' to failing.


My coils have had it at about 55k miles because of the spade connections on the coils them selves. @Andyc's 929 blade stick on coils are working well

Yes, the spade connectors on the coils are one of the bits that are 'going' on mine. They will be ok for a bit...

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