Spark plug gap

[ReelDrag]

I've noticed a few people on this forum recommend a .040 gap instead of .030 which is what the manual recommends for my 92 Johnson 115 cf. What is the reason for this? If the motor will run better with the .040 gap why isn't that stated in the manual? Does a wider gap run hotter? I understand the older motors used a .040 gap, so why did they change it?

 

[OBJ]

Re: Spark plug gap

Don't know the reason ReelDrag....but I do know it makes the engine idle smoother. Got a 86' 90hp Johnny. Plugs set a .040. Great top end.

 

[DJ]

Re: Spark plug gap

I believe it was a later bulletin. The .40" was mentioned for engines that idle a lot. Not all of them do.

 

[springbok]

Re: Spark plug gap

I was wondering about the same thing....<br />I have a 1988 25HP Evinrude. The manual reccomends .030 as well... I do a lot of trolling so I'm gonna try gaping at .040 as well.<br />The only question I have, will the extra gap put more demand on the coils, will it shorthen the life of a coil or is it so minor that it doesn't really matter?<br />Thanks....

 

[DJ]

Re: Spark plug gap

Nope. There's more than enough oomph to jump that gap. Heck, we test them by making them jump a 7/16" gap.

 

[springbok]

Re: Spark plug gap

Perfect, thanks...<br />So should there be a noticable difference at idle?<br />What about top end, will it increase rpm and or speed?<br />Thanks

 

[DJ]

Re: Spark plug gap

You'll have to be the judge of that.

 

[Imtrying]

Re: Spark plug gap

Can't set the gap with my plugs cuz they don't have an eletrode? Whats the deal with those? 1974 70hp Johnson.....Dan

 

[JB]

Re: Spark plug gap

My Johnson Service Manuals of 1964 and 1969 both call for .030 gaps on all engines with gappable plugs. . .going back to 1922.<br /><br />They also call for 30 weight non-detergent motor oil and aviation (white) gas. Don't want to do that, either.<br /><br />Many of us have learned over time that we can use the cooler plugs (J4) gapped at .040 and get better all-speeds performance without fouling at low speeds.<br /><br />That varies from engine to engine. Not enough to cause major trouble, but enough so that John Doe's engine might perform better with .035 gap and John Smith's with .040.<br /><br />I think that gaps from .030 to .040 will work (Champion plugs only), just as J6 plugs can be used where J4s are normally called for and vice versa.<br /><br />I think it is usage that makes differences matter.

 

[rickdb1boat]

Re: Spark plug gap

Imtrying<br /><br />Although I did not find a 1974 listed, I did find a 1975 70 HP which uses Champion L77JC4 or QL77JC4 gapped at .030.(Better at .040) I'm sure your motor can use these with no problem

 

[ReelDrag]

Re: Spark plug gap

Well, I tried the .040 gap with a new set of QL77JC4 plugs. My motor does not like that at all. Backfire out the exhaust when starting. Rough idle. Back to the QL82C gaped at .030.

 

[Dhadley]

Re: Spark plug gap

ReelDrag -- your 115 will run perfect on those QL77JC4 plugs. If it backfired out the exhaust, make sure there arent 2 plug wires crossed. Very common and easy to do.

 

[DJ]

Re: Spark plug gap

ReelDrag<br /><br />Agree with Dhadley. A change of plug or a change of gap is NOT going to cause what you describe. Something else is amiss.<br /><br />The changes in performance (idle, cruise, etc) are subtle, at best, but noticeable.<br /><br />NOTHING like what you describe.

 

[ReelDrag]

Re: Spark plug gap

No wires crossed. It runs ok on the QL77JC4 plugs as long as they're gaped at .030 to .035, but sounds a lot stronger and smoother with the QL82C. I don't run WOT much and the QL77JC4 plugs foul after a few hours of use.

 

[shade788]

Re: Spark plug gap

Do the QL77JC4 and L77JC4's foul up fast? I just got done putting in a set of L77JC4's in my 60HP 2 Cylinder Johnson.<br /><br />I bought it last year and it had NGK B9HS-10's.<br /><br />I put the Champions in and turned it over for the for the first time this season. It cranked right up with a little choke.<br /><br />With the NGK's in last season I had to choke it a lot more and give it a little fast idle.<br /><br />These Champion plugs rock!