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DUCAUDI
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PostPosted: 19:32 - 15 Oct 2019    Post subject: Spark plug question Reply with quote

Hi guys

Just a quickie this time. Ordered a set of spark plugs from Fowlers by selecting my bike from the list, CR8E was identified as the correct spark plug for my bike.

Went to remove the old spark plugs and although they look identical to the new ones (same total length, seat position, thread etc) the code on the old ones is CR9E.

I fitted them anyway and the misfire/splutter that was there before is still present (so I'm now thinking carbs), other than that everything else seems to be running the same as it was before.

Is this something I should be concerned about? Could it be I was sent the wrong spark plugs for my bike? Or maybe because they're nearly identical despite the difference in code the previous owner just used CR9E instead of CR8E because that's all they could get hold of at the time and didn't actually make a difference to the running of the bike?

Obviously each character in the code means something, probably a reference to the specs of that particular spark plug. Can someone explain what all the numbers and letters mean please?

Many thanks!
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Howling Terror
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PostPosted: 19:36 - 15 Oct 2019    Post subject: Reply with quote

Hi,

Tell us the make model and year of your bike and I bet someone on here will tell you.
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Nobby the Bastard
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PostPosted: 19:37 - 15 Oct 2019    Post subject: Reply with quote

The number 8 plug is a slightly cooler one than a number 9 plug. The cooler the plug, the smaller the bowl round the electrode is.

The bigger the bowl, the bigger the the initial detonation is becuase it can hold more mixture. If it is difficult to start and tends to run cool, go for a hotter plug, conversely a hotter plug can cause overheating and knocking.
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DUCAUDI
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PostPosted: 19:51 - 15 Oct 2019    Post subject: Reply with quote

Howling Terror wrote:
Hi,

Tell us the make model and year of your bike and I bet someone on here will tell you.


Good point that might help! 2002 FZS600 Fazer



Nobby the Bastard wrote:
The number 8 plug is a slightly cooler one than a number 9 plug. The cooler the plug, the smaller the bowl round the electrode is.

The bigger the bowl, the bigger the the initial detonation is because it can hold more mixture. If it is difficult to start and tends to run cool, go for a hotter plug, conversely a hotter plug can cause overheating and knocking.


That's really helpful, thank you. Presumably then, assuming Fowlers database is correct and the original fitted plug would have been an 8, the previous owner may have changed from an 8 to a 9 to cure poor starting?
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Nobby the Bastard
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PostPosted: 20:09 - 15 Oct 2019    Post subject: Reply with quote

Possibly.

It's also just as possible that they'd heard some bollocks about hotter plugs increasing power.

Try the 8s and see what happens. If it runs like a bag of nails, try putting the 9s back in.
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Nobby the Bastard
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PostPosted: 20:20 - 15 Oct 2019    Post subject: Reply with quote

Feathers McGraw wrote:
Nobby the Bastard wrote:
The number 8 plug is a slightly cooler one than a number 9 plug.

Opposite way round.

Higher digit = cooler plug Thumbs Up


Congratulations on taking the time to look up my answer on Google to see if I'm wrong.
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DUCAUDI
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PostPosted: 21:52 - 15 Oct 2019    Post subject: Reply with quote

Nobby the Bastard wrote:
Possibly.

It's also just as possible that they'd heard some bollocks about hotter plugs increasing power.

Try the 8s and see what happens. If it runs like a bag of nails, try putting the 9s back in.


But, while you say increasing spark plug temp doesn't increase power, would reducing temp potentially reduce power?
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Nobby the Bastard
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PostPosted: 22:05 - 15 Oct 2019    Post subject: Reply with quote

Tuberculosis wrote:
Nobby the Bastard wrote:
Possibly.

It's also just as possible that they'd heard some bollocks about hotter plugs increasing power.

Try the 8s and see what happens. If it runs like a bag of nails, try putting the 9s back in.


But, while you say increasing spark plug temp doesn't increase power, would reducing temp potentially reduce power?


A plug with a bigger bowl will result in a slightly advanced ignition due to greater propagation of the burn but as to whether this will result in more power or whether itll just result in more heat and the likelihood of knocking is anyone's guess.
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Polarbear
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PostPosted: 22:55 - 15 Oct 2019    Post subject: Reply with quote

I would very much doubt the difference between an 8 or 9 rated plug will be even noticeable on a larger cc lower tuned 4 stroke. However my standard statement in all cases like this is go with the manufacturer recommendation as long as your engine is standard.

When I had 2 strokes it could be critical especially after so home made tuning. Whistle It could be the difference between a solid piston or one with a hole in it Shocked

You haven't got that worry Thumbs Up
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DUCAUDI
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PostPosted: 22:58 - 15 Oct 2019    Post subject: Reply with quote

Polarbear wrote:
I would very much doubt the difference between an 8 or 9 rated plug will be even noticeable on a larger cc lower tuned 4 stroke. However my standard statement in all cases like this is go with the manufacturer recommendation as long as your engine is standard.

When I had 2 strokes it could be critical especially after so home made tuning. Whistle It could be the difference between a solid piston or one with a hole in it Shocked

You haven't got that worry Thumbs Up


Thanks for this. And I take your point that the difference would be minimal but I much like yourself always prefer to go with standard manufacturer's recommended parts etc. Although Fowlers specified an 8, the ones that came out were a 9, in addition I have since watched a YouTube video of a spark plug change on a FZS600 and I noticed the ones that came out of that were 9s too :-/
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Polarbear
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PostPosted: 23:20 - 15 Oct 2019    Post subject: Reply with quote

Tuberculosis wrote:


Thanks for this. And I take your point that the difference would be minimal but I much like yourself always prefer to go with standard manufacturer's recommended parts etc. Although Fowlers specified an 8, the ones that came out were a 9, in addition I have since watched a YouTube video of a spark plug change on a FZS600 and I noticed the ones that came out of that were 9s too :-/


I have just braved the cold to go out to the garage and pull the plug cap of a cylinder on our year 2000 Fazer hack which has gone 40000 miles with as much abuse and as little maintenance as possible and is still going strong.

As well as getting a dirty hand I can confirm the plugs fitted to it are 8's.
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Fizzer Thou
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PostPosted: 23:29 - 15 Oct 2019    Post subject: Reply with quote

The correct NGK spark plug for the FZS600 is the CR8E.

The higher the heat range number specification,the colder or harder conditions the plug will run in.

As a good example,my old Honda CB550K3 (c.1978) usually ran a D7 type spark plug.As I also rode a CB750F2 and the plugs were a D8,I tried the cooler plug in the CB550.When I say that I tried them,they did not work at all.As soon as I reverted back to the D7 type,the CB550 ran perfectly.
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DUCAUDI
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PostPosted: 00:18 - 16 Oct 2019    Post subject: Reply with quote

Polarbear wrote:
I have just braved the cold to go out to the garage and pull the plug cap of a cylinder on our year 2000 Fazer hack which has gone 40000 miles with as much abuse and as little maintenance as possible and is still going strong.

As well as getting a dirty hand I can confirm the plugs fitted to it are 8's.


Wow thank you for doing that for me. I feel better now. I also feel guilty too, but you are a Polar Bear after all!
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