Spark plug change interval

[ew1usnr]

Dennis, as long as you are spending this much attention to the plugs and ignition system it may be worthwhile to try indexing your plugs. This article says a 1-2% performance loss can occur from poorly oriented plugs.

Thanks, Jeff.

Before changing my plugs I had watched a video about indexing plugs using washers to change the final spark plug tip orientation. That did not seem like a good idea because it would change the depth of the plug into the combustion chamber.

The article that you provided described how to index the plugs without using washers. It explains that all the plugs are different and to simply use trial and error to see which plug fits best into each hole.

Darn. I wish that I had marked the direction of the plug tips with a sharpie.

Logically, it seems that it would make a difference if plug tip faced towards the center of the combustion chamber rather than facing backwards towards a cylinder wall.

Indexing the plugs is supported by this explanation where a guy tried changing the position of the spark plug while working on a one-cylinder engine. He said that the orientation of the spark plug tip made an obvious audible difference and changed the RPM from 2000 to 1700:

"A few years back, I played with a single cylinder ATV and noticed that a spark plug fired best at a certain rotational position. The results were measured in idle RPM. At one idle setting, the RPM ranged from 2000 down to 1700. The change was audibly different - very obvious.

When I hit the optimum spot, I pulled the head off the cylinder and looked where it was. The arm holding the gap was pointed AWAY from the center of the combustion chamber.

It's not about increased horsepower anymore. It's about SAVING GAS. Burning your fuel more efficiently will increase your gas milage, with fewer trips to the pumps. Mind you it's not a dramatic change.... But a lot of little still makes a lot."

See: http://www.doityourself.com/forum/pa...washers.html#b