why only 2?
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Road Captain
Joined: Feb 2009
Posts: 502
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From: lone grove, oklahoma
why only 2?
I was looking over my ultra today and suddenly realized that it only has two spark plugs. My old honda (05vtx 1300) had four, I know the honda was water cooled and carbureated but why would it have four plugs and harley's only have two.
Road Warrior
Joined: Feb 2007
Posts: 1,577
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From: Lake Jem FL (pop 35)
Actually... Some V Twins have 4 plugs.
A Shovelhead has a hemispherical combustion chamber and a domed top piston. The flame front sometimes does not get all the way across/around the piston and you lose performance. Performance minded guys would have their heads machined to have a plug from two sides to get an even burn.
Just because a bike has two cylinders, does not mean it will always have only two plugs.
A Shovelhead has a hemispherical combustion chamber and a domed top piston. The flame front sometimes does not get all the way across/around the piston and you lose performance. Performance minded guys would have their heads machined to have a plug from two sides to get an even burn.
Just because a bike has two cylinders, does not mean it will always have only two plugs.
Ultimate HDF Member
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Ultimate HDF Member
Joined: Dec 2006
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From: The Desert SouthWest
I say makers should figure out how to build it to run well with one plug, seems a bit silly - short of a race car - to need two plugs to fire a cylinder.
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Road Master
Joined: Aug 2008
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From: Sunny Seattle, WA
That means your Harley is twice as good.
Ultimate HDF Member
Joined: Aug 2008
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From: eastern oklahoma
it was an old trick with bmw motorcycles in years to twin plug the heads so that the flame travel of the combustion would be more complete. with the newer head designs it's no longer needed. remember in the mid nineties the sportster sport had two per cylinder? damm, now i went and made myself feel old.