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failing spark plugs!

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Tricky.
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failing spark plugs!

Post by Tricky. on Sat 05 Mar 2016, 7:51 pm

under hard use its known that the cb eats sparks plugs and ive come to live with that, however, ive got through three plugs in a month now, anyone know why/what the cause could be?
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Beresford
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Re: failing spark plugs!

Post by Beresford on Sat 05 Mar 2016, 7:56 pm

Can you put up a clear picture showing the electrodes, maybe we can tell something from that ?
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wornsprokets
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Re: failing spark plugs!

Post by wornsprokets on Sat 05 Mar 2016, 7:58 pm

Four strokes engines dont generally used spark plugs it was old two strokes that did, some two strokes back in 70s did so it wasnt uncommon to have few under the seat. My cb doesnt use spark plugs i changed them once,(1) what mileage is your cb(2) is it a carb problem(3) hard use as in racing, i have my cb over the tone it doesnt affect plugs.(4)have u a haynes manual it shows what problems it could be. I say its a carb problem or high mileage is engine worn out
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Tricky.
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Re: failing spark plugs!

Post by Tricky. on Sun 06 Mar 2016, 9:07 pm

the failed plugs look fine when removed, good colour, and spark ok when removed from the engine, but when back in the engine they just dont have the power to ignite. hard use is track days and racing, a few other racers also have commented that they get through more plugs than if road riding, but over the last year, and more recently, it seems to be worse.
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wornsprokets
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Re: failing spark plugs!

Post by wornsprokets on Sun 06 Mar 2016, 9:14 pm

Have u done a compression test,  had valves been checked
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Beresford
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Re: failing spark plugs!

Post by Beresford on Sun 06 Mar 2016, 10:03 pm

@Tricky. wrote:but when back in the engine they just dont have the power to ignite.



Pardon, come again ?
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eternally_troubled
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Re: failing spark plugs!

Post by eternally_troubled on Mon 07 Mar 2016, 12:24 pm

@Beresford wrote:
@Tricky. wrote:but when back in the engine they just dont have the power to ignite.




Pardon, come again ?

I think he's trying to say that they spark when you have them out but when you put them in they don't (when you have 120 psi of air/fuel mixture to spark through etc).

Tricky, are you sure it's not just that the race environment makes CB500 coils degrade a lot quicker, meaning that they end up only working with new plugs after a while? (i.e. it's not the plugs that are broken but your coils!)
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Tricky.
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Re: failing spark plugs!

Post by Tricky. on Mon 07 Mar 2016, 6:56 pm

@wornsprokets wrote:Have u done a compression test,  had valves been checked

i havent yet, the compression tester ive got is for cars and wont fit down the plug-cap holes.
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Tricky.
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Re: failing spark plugs!

Post by Tricky. on Mon 07 Mar 2016, 7:02 pm

@eternally_troubled wrote:

@Beresford wrote:


@Tricky. wrote:but when back in the engine they just dont have the power to ignite.






Pardon, come again ?



I think he's trying to say that they spark when you have them out but when you put them in they don't (when you have 120 psi of air/fuel mixture to spark through etc).

Tricky, are you sure it's not just that the race environment makes CB500 coils degrade a lot quicker, meaning that they end up only working with new plugs after a while?  (i.e. it's not the plugs that are broken but your coils!)

yes that was the sort of thing i was trying to say, lol. 



never thought about the coils idea. any recommendations on where to get some new ones, other than china, unless they are actually good?
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geoffnorfolk
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Re: failing spark plugs!

Post by geoffnorfolk on Tue 08 Mar 2016, 10:13 am

That sounds very strange as you wouldn't expect both coils to have partially failed at the same time. When the plug problem appears, does the bike still start up on just one cylinder which I'd expect? If so, swap the plugs over and see if the non-firing cylinder swaps over as well which will prove its the plug that's the problem.  You could then do a similar thing with the coil/HT leads/plug caps if necessary to rule them out.
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Tricky.
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Re: failing spark plugs!

Post by Tricky. on Tue 08 Mar 2016, 7:41 pm

@geoffnorfolk wrote:That sounds very strange as you wouldn't expect both coils to have partially failed at the same time. When the plug problem appears, does the bike still start up on just one cylinder which I'd expect? If so, swap the plugs over and see if the non-firing cylinder swaps over as well which will prove its the plug that's the problem.  You could then do a similar thing with the coil/HT leads/plug caps if necessary to rule them out.

when it wasnt firing on one cylinder, the first thing i did was to swap the plug over to the other side, and this confirmed it was knackered, replace with a new plug and away we go. twice now on the left cylinder and once on the right.
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badseeds
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Re: failing spark plugs!

Post by badseeds on Wed 16 Mar 2016, 7:06 pm

@Tricky. wrote:under hard use its known that the cb eats sparks plugs....

I'm clearly not trying hard enough!
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skyrider
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Re: failing spark plugs!

Post by skyrider on Wed 16 Mar 2016, 8:31 pm

@badseeds wrote:

@Tricky. wrote:under hard use its known that the cb eats sparks plugs....



I'm clearly not trying hard enough!

could do better must try harder Laughing Laughing Laughing
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davebike500
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Re: failing spark plugs!

Post by davebike500 on Thu 17 Mar 2016, 11:40 am

I been bouncing CB500's off the rev limiter since 2003 never killed a plug yet  !
Las set EIX did 35K + Miles

If you bike is killing plugs I say the mixture is wrong very wrong !
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Beresford
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Re: failing spark plugs!

Post by Beresford on Thu 17 Mar 2016, 3:39 pm

@davebike500 wrote:If you bike is killing plugs I say the mixture is wrong very wrong !

It does sound like the plugs are overheating. That's usually because of wrong mixture, wrong timing (too advanced - but I don't think it's adjustable on the CB ) or wrong plugs.
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Tricky.
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Re: failing spark plugs!

Post by Tricky. on Thu 17 Mar 2016, 11:45 pm

plugs always come out looking a good colour. cr9e.

muttley1
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Re: failing spark plugs!

Post by muttley1 on Thu 17 Mar 2016, 11:57 pm

Never had a failing plug issue in 14 years of various cb5's. Sounds like an ol' 2 stroke heat range issue if anything. An MZ I had way back when used so just stop after 20 miles or so if I didn't have a highter heat range plug than spec for road use. It'd go fine when everything had cooled off.

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