.30 Vs .40 plug gap

[randyray41]

I hear a lot of people say that gapping a Champion QL77JC4 to .40 instead of the recommended .30 provides a smoother idle. Is this correct information?

1978 70hp Evinrude

 

[fhhuber]

Might help idle... but as rpm and load on the engine increase you could start getting misfires.

Pugs out and using a spark tester you can get the spark to jump up to 1 inch gap. As you increase pressure you decrease the gap that can be jumped

 

[jimmbo]

Might help idle... but as rpm and load on the engine increase you could start getting misfires.

Pugs out and using a spark tester you can get the spark to jump up to 1 inch gap. As you increase pressure you decrease the gap that can be jumped

I guess they are counting on gas getting in the gap and thus ensuring the spark ignites it

 

[boobie]

With .030 " plug gap you get better plug mileage.

 

[Vic.S]

I hear a lot of people say that gapping a Champion QL77JC4 to .40 instead of the recommended .30 provides a smoother idle. Is this correct information?

1978 70hp Evinrude

Originally the gap would have been specified as 0.040". Sometime in the late 1980's the recommended plug gaps were all revised to 0.030". Allegedly this was to increase plug life.

Use 0.030 or 0.040 or something in between, what ever seems to work best for your engine.

 

[AventuSD]

I have an 84 115 and it seems like it idles much smoother gapped near .040