Stump the Chumps-intermittent misfiring (2015)

PM999S said:

Thanks guys - after all the wiring work it turned out to be a duff NGK spark plug. Brand new but my own fault for trusting to eBay - never again!

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I’m like a broken record on this topic!

My spark plug rules:
Always try new plugs first for ANY ign related symptoms.
Buy a box of plugs so you’ve always got new ones on hand to try.
Buy from a trusted source to minimise risk of counterfeit plugs.
Even new genuine plugs can be duff from the box, so don’t assume ‘it can’t be the plugs’!

A lot of of old bikes that are running a bit rich, burning a bit of oil, and seldom get run at WOT to burn the plugs clean, are susceptible to plug fouling. Plug fouling is a real thing. It can give all sorts of running issues that you will be convinced cannot possibly be down to humble spark plugs.

Most plugs these days have resistors inside, as do many plugs caps and plug leads. Lack of care in choosing can mean you’re suppressing most of your spark before it happens!

Spark plugs can degrade over time, they’re not a work / don’t work kinda thing.

So don’t be a mug... change your plug...!!