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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
What are your thoughts on Spark Plugs for a Twin?
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<blockquote data-quote="Tom Gaynor" data-source="post: 4544" data-attributes="member: 4034"><p><strong>Plug ratings</strong></p><p></p><p>This is the second thread I've read recently (the other was jtan and may be the same people) which sought to cure plug fouling by going to iridium plugs. I have no feelings about iridium either way, but in each case the plug that fouled was an NGK 7. This is far too hard (cold) for a Vincent unless to some extreme level of tune - an AJS 7R or 350 Manx runs on an NGK 8. NGK BP6 is actually NGK's recommendation for a Vincent twin (I have an obsolete NGK publication that covers Vincents, Rudges and Sunbeams among many others). I've also used 5's to mitigate oiling symptoms, like an enforced plug change every 150 miles. The disease was cured by fitting new pistons and valve guides - whereupon the symptoms disappeared and I could go back to a 6 in the front. However for 6000 miles before I bit the bullet I ran a 5 in the (offending) front and 6 in the rear and while the 5 looked less like a plug and more like a slag heap when examined, never actually stopped firing.</p></blockquote><p></p>
[QUOTE="Tom Gaynor, post: 4544, member: 4034"] [b]Plug ratings[/b] This is the second thread I've read recently (the other was jtan and may be the same people) which sought to cure plug fouling by going to iridium plugs. I have no feelings about iridium either way, but in each case the plug that fouled was an NGK 7. This is far too hard (cold) for a Vincent unless to some extreme level of tune - an AJS 7R or 350 Manx runs on an NGK 8. NGK BP6 is actually NGK's recommendation for a Vincent twin (I have an obsolete NGK publication that covers Vincents, Rudges and Sunbeams among many others). I've also used 5's to mitigate oiling symptoms, like an enforced plug change every 150 miles. The disease was cured by fitting new pistons and valve guides - whereupon the symptoms disappeared and I could go back to a 6 in the front. However for 6000 miles before I bit the bullet I ran a 5 in the (offending) front and 6 in the rear and while the 5 looked less like a plug and more like a slag heap when examined, never actually stopped firing. [/QUOTE]
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Tech. Advice: Series 'B' / 'C' 500cc/1000cc Bikes
What are your thoughts on Spark Plugs for a Twin?
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