Middle cylinder stopping firing

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shunter
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Middle cylinder stopping firing

Post by shunter »

Hi everyone it's been a while since I have been on for a couple of reasons, last April I got diagnosed with bowel cancer so that took last years riding out and this year I gave been working on a CB750K2. I have been out on the kettle quite a bit recently and the power was dying after about 20-30 Mike's three times I limped it home to find the centre exhaust almost cold, I put a new plug in away she goes no problem but the plug does not look bad, last time I also changed the HT cap and I took it for two runs one 50 miles and one about 45 miles and it ran great. Today I only got about 7 miles when the power went I stopped and same again centre pot had stopped working I put a new plug in and it ran great for another 40 odd miles. Any tips what could be causing this. Many thanks.
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canaletto5
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Re: Middle cylinder stopping firing

Post by canaletto5 »

Hi

I hope you're over the worst with your health problem.

It may be the heat range on the plug needs adjusting (what are you usng at the moment?) or maybe the carb is running a bit lean. If the plug is dry, Try enriching the mixture setting a bit.

Kev
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itsnotateapot
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Re: Middle cylinder stopping firing

Post by itsnotateapot »

is the bikes charging system working ok, poor battery will drop a cylinder.
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shunter
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Re: Middle cylinder stopping firing

Post by shunter »

Thanks, I do hope I am over the worst now as it was a big op at 4.5 hours. I will check both plugs and charging and report back. I think the plugs are B8ES but will confirm. The charging was ok as I did have an issue a while ago but will not do any harm to check. Thanks.
barney01
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Re: Middle cylinder stopping firing

Post by barney01 »

Where do you get your plugs from? There are many fakes circulating on Ebay. :shock:
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Alan H
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Re: Middle cylinder stopping firing

Post by Alan H »

Swap the centre and an outside plug and see which pot runs. That'll prove the plug or point at summat else.

Anyway, who's Mike? :|
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shunter
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Re: Middle cylinder stopping firing

Post by shunter »

Ah that's manx for miles Alan :oops: . I did swop them over after cleaning them and all three pots fired up but the centre one died again later on. It does seem plug related as soon as you change the plug it works. I did buy the plugs from Ebay but from a recognised supplier (I hope) as I had heard about the NGK fakes. I will go and check what the plugs are that are in the bike.
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shunter
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Location: Isle of man

Re: Middle cylinder stopping firing

Post by shunter »

I have just checked the plugs and they are NGK B8ES, the one that had stopped working was wet at the electrode I forgot to say in the last post. I have tested the battery with a proper battery tester and that's coming up with good battery. Is there another type of plug worth trying first. As I know if I put the other plug back it all will work for a while. Thanks.
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canaletto5
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Re: Middle cylinder stopping firing

Post by canaletto5 »

Try a B7ES but don't go any hotter than that or you may get pre-ignition. You can also try iridium plugs (start with a B8ES equivalent) they do perform a lot better. No cheap though
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stevewharton
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Re: Middle cylinder stopping firing

Post by stevewharton »

canaletto5 wrote:Try a B7ES but don't go any hotter than that or you may get pre-ignition. You can also try iridium plugs (start with a B8ES equivalent) they do perform a lot better. Not cheap though
If it does end up being a simple spark plug problem, (is anything ever simple :roll: ) i'd go iridium. I've had the same NGK iridium plugs in mine for the last 10 years (40,000ish miles) and never missed a beat. Try buying local or have a good look on ebay for the best price, but I'd recommend buying from a reputable company. HTH
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