Spark plug length - More revs?

A reference for the PWK carbs...
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gsa102
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Spark plug length - More revs?

Post by gsa102 »

I was riding my 96 200 last week, and wanted to share something it found with my bike. I fouled a plug at a buddy's house the and he gave me a used 1/2" reach plug to use (rather than the standard 3/4"). It was a 7 and I normally run 8. I noticed that the bike would rev way more on top than it did before, and the jetting felt better overall. Anybody else ever notice this? Was it a change in combustion chamber volume, or the heat range of the plug because it is too rich?
This is my rifle, this is my gun, the YZ to go fast, the KDX is for fun!

96 KDX 200, 09 YZ 250
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fuzzy
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Re: Spark plug length - More revs?

Post by fuzzy »

Interesting. Yes, you took CC's out of the head, which would lower static compression and lend itself to more overrev. I would advise against running a 7 heat range plug.
'91 KDX 200 Project $300 KDX
'95 KDX 200 Project $600 KDX
'94 WR 250 Always a project
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gsa102
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Re: Spark plug length - More revs?

Post by gsa102 »

I replaced it with a new number 8, 3/4 reach plug and the overrev went away. We were riding open fields with the kids when I had the short plug in, so I did not notice if it affected the low end.
This is my rifle, this is my gun, the YZ to go fast, the KDX is for fun!

96 KDX 200, 09 YZ 250
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Tioli
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Spark plug length - More revs?

Post by Tioli »

Thanks for sharing that gsa102. There would be a reason for it, what it did is the interesting thing.

I'm thinking the combustion pressure is now taking longer to get to the piston. This makes the preasure get there later efectvly retarding the ignition and that will do it.
2001 KX125 with a 1997 KDX Tioli Hp motor

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Trials.com.au / Forum / All about...me! / My long time friend the prancing horse / page 9
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