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.

 

you only need 1 per cylender. If you install 2 you are giving up some head space to a spark plug, therefore the valves need to be smaller. This could have something to so with it??

 

they eliminated them with the introduction of the kunneauter valve. Could resist, let the fun begin.

 

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.

 

Harley sells SE heads with 4 plugs, so if you need more than two, you've got an option.

 

Your Honda was a 2 cylinder wasn't it? Just kidding. See how much cheaper the Harley is for tune ups.

Toby

 

you should put 2 in your pockets so you have 4 like your ol honda

 

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.

 

That means your Harley is twice as good.

 

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.