.040 plug gap seems a bit much

[huntin dawg]

I was looking at my Johnson repair manual and it says to gap the plugs for my 4.5 hp at .040 using a Champ L77JC4. That seems like a huge gap for such a cool plug. Opinions from the experts please.

Thanks.

 

[1946Zephyr]

Re: .040 plug gap seems a bit much

.020 gap is pretty typical for all outboards

 

[bktheking]

Re: .040 plug gap seems a bit much

.020 is typical for points maybe, .030 or .040 are the only gaps I show from 2-40 hp from 73-90 in my manual.

 

[1946Zephyr]

Re: .040 plug gap seems a bit much

Oh wait a minute, my mistake. The L77JC4 would gap at .030. I was thinking of the points.....DUHH

 

[F_R]

Re: .040 plug gap seems a bit much

I was looking at my Johnson repair manual and it says to gap the plugs for my 4.5 hp at .040 using a Champ L77JC4. That seems like a huge gap for such a cool plug. Opinions from the experts please.

Thanks.

The .040" is probably correct for the L77JC4 plugs used with CD ignition. In fact, last time I checked that is what they came pre-gapped at.

 

[1946Zephyr]

Re: .040 plug gap seems a bit much

good point. What year motor are you working on?

 

[bktheking]

Re: .040 plug gap seems a bit much

.040 is correct for that motor, it has to do with CD ignition being stronger than conventional point/condensor , wider gap helpes eliminate lean burning as the spark distance and voltage is stronger.

 

[huntin dawg]

Re: .040 plug gap seems a bit much

good point. What year motor are you working on?

1983

 

[bktheking]

Re: .040 plug gap seems a bit much

1983

Right plug, right gap.

 

[kenmyfam]

Re: .040 plug gap seems a bit much

I think you are correct.

 

[JB]

Re: .040 plug gap seems a bit much

Over the years published plug gap specs, along with fuel mix specs for many JohnnyRudes have been changed and rechanged.

You will find some books say .030" and others .040". I would be inclined to take the advice of F R and/or Joe Reeves about which to use with which plug.

 

[seahorse5]

Re: .040 plug gap seems a bit much

About 20 years back OMC did publish a .040" spark plug gap on some motors. They soon found out that it was better to use a .030" gap and all information since then shows to use a .030" gap instead of a .040. They sent out a service bulletin even, to tell about changing the spec to .030".

 

[tashasdaddy]

Re: .040 plug gap seems a bit much

^^ very true. but if you idle alot and the plugs foul, you can open the plug to as much as .040, to cut down on slow speed fouling.

 

[Knightgang]

Re: .040 plug gap seems a bit much

Just a word of caution. Never trust the GAP on a pre-gapped plug. They may be preset at the mfg., but they get banged around during shipping and the gap can close up. Always double check your gap settings...

 

[jasper60103]

Re: .040 plug gap seems a bit much

yea, my manual says .040 (QL77JC4) for my motor as well. Currently running with .030 as directed by Champion spark plug chart.

 

[justbehindit]

Re: .040 plug gap seems a bit much

My 1982 Johnson 70 hp is spec'd out at .040, and in fact all of the motors in the OMC manual show .040.

 

[Vic.S]

Re: .040 plug gap seems a bit much

My 1982 Johnson 70 hp is spec'd out at .040,

Maybe true but the recommended gap for (practically) all is now 0.030".

Usual recommendation from folks on here is to use which works best 30 thou or 40 thou (no reason for not splitting it down the middle and going for 35 I guess)

i believe, but may not be right, that the change was to extend plug life.

I only recently discovered the change so my '84 model was still running at 40 until last year. Now reset to 30 but I notice no change is operation even though almost never run at high revs as its an auxiliary for a small sail boat.