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SOHC.co.uk Forums => CB500/550 => Topic started by: DomP on July 06, 2024, 11:39:52 AM

Title: Weak spark?
Post by: DomP on July 06, 2024, 11:39:52 AM

I'm sure I'm missing something here but I'm having a few firing issues, currently no.2 and 4 are not firing well, if I remove a plug and hold it against the block it won't spark unless I hold it just close so that it arcs.  Touching I get nothing, what is the cause of this, a poor ground connection?

Title: Re: Weak spark?
Post by: Bryanj on July 06, 2024, 01:48:41 PM

More likely fouled plug or loose plug cap

Title: Re: Weak spark?
Post by: Johnwebley on July 06, 2024, 01:52:02 PM

2 and 4 use different coils, breakers etc,

They are paired 1 and 4
2 and 3

Have you replaced any parts?

Have you got resistance plug caps?

Might be worth checking the resistance, as they get older, they can increase the resistance, causing issues



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Title: Re: Weak spark?
Post by: DomP on July 06, 2024, 03:47:08 PM

Doh!  Rich sooty plugs, proper schoolboy error chaps.

Title: Re: Weak spark?
Post by: DomP on July 07, 2024, 02:56:03 PM

Or was it?!   The same thing happened today so I pulled all four 'new' spark plugs and tested them with my multimeter, two are showing a resistance between the terminal and the outer body.  Presumably this is indicating a breakdown of the inner core? 

New D7EA plugs ordered from The Green Sparkplug Company so hopefully that will solve that problem, whether my plugs were fakes or somehow I've caused them to fail I don't know.

Title: Re: Weak spark?
Post by: McCabe-Thiele (Ted) on July 07, 2024, 03:35:49 PM

FWIW when I clean spark plugs I brush the end of the plug then I heat it in a gas flame on my hob to burn off any deposits on the bit you can't get at - the inside insulation.

Title: Re: Weak spark?
Post by: Johnwebley on July 07, 2024, 04:00:41 PM

Quote from: DomP on July 07, 2024, 02:56:03 PM

Or was it?!   The same thing happened today so I pulled all four 'new' spark plugs and tested them with my multimeter, two are showing a resistance between the terminal and the outer body.  Presumably this is indicating a breakdown of the inner core? 

New D7EA plugs ordered from The Green Sparkplug Company so hopefully that will solve that problem, whether my plugs were fakes or somehow I've caused them to fail I don't know.

Are you riding the bike fast, or hard enough?

Maybe the standard slow running is to rich?

Don't be afraid to experiment,

Open the slow running screw half a turn,

See what happens,

If you do ride slower

Try a hotter plug,

My 500 runs the same as 750 and 400 with no problem

Remember, if you alter settings, you can also return to previous



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Title: Re: Weak spark?
Post by: DomP on July 07, 2024, 07:29:55 PM

I've tried that with a lighter Ted, the main problem seems to be the plugs must have shorted internally. 

Thanks John, I've had the screws out 2 turns but up until yesterday I had no working speedo so road testing wasn't really possible, well that and the crap weather!