Spark Plugs

[Flemith]

I'm looking to replace my spark plugs in both my motors and I have a question. What is the difference between QL77JC4 plugs and L77JC4 plugs?

Also, what should the plugs be gapped at for a mid-80's 35HP Evinrude?
I cant seem to find my manual for the motor. I know my 7.5HP Evinrude of the same era is .040".

Thanks in advance

 

[Vic.S]

Re: Spark Plugs

The Q denotes an inductively suppressed plug.

They are used in place of resistively suppressed plugs with CDI ignition systems

See http://members.iinet.net.au/~pauldawson/iame26-spark-plugs.PDF

0.030" is now the recommended gap for both of those, but if either runs better at 0.040" use that .

 

[tashasdaddy]

Re: Spark Plugs

the Q stops interference with radios, fish finders, etc.

 

[Flemith]

Re: Spark Plugs

The Q denotes an inductively suppressed plug.

They are used in place of resistively suppressed plugs with CDI ignition systems

See http://members.iinet.net.au/~pauldawson/iame26-spark-plugs.PDF

So, what I got out of that link was that using L77JC4 plugs could cause a misfire because they reduce the arc duration by half with my motor. (Could this be the reason why my motor doesn't like to idle?) The motor has been running with these plugs for as long as I've owned it. I read that they also affect electronic accessories, which I don't have.

0.030" is now the recommended gap for both of those, but if either runs better at 0.040" use that .

So, has the recommended gap changed? The manual I have for the motor says .040".

the Q stops interference with radios, fish finders, etc.

Well, I'm not too worried about interference with radios or fish finders as my boat has no electronic accessories. Up until this year, the boat didn't even have working lights.

 

[Vic.S]

Re: Spark Plugs

using L77JC4 plugs could cause a misfire because they reduce the arc duration by half with my motor

No. what it is saying is that plugs with a resistive suppressor will do that (Plugs with R as the first letter for example) L77JC4 are not suppressed at all.

However further on it seems to imply that a non suppressed plug could cause interference that affects its own ignition sytem as well as other electronics. On that basis the Q plugs are the better choice ( more expensive too)

I'm not an electronics engineer but that's my understanding from reading the article.

Yes the recommended gaps for practiclly the whole range of outboards have been revised. A few years ago now IIRC but I forget exactly when. I have noticed that Joe Reeves says some run better at 0.040" and if they do use that but otherwise adopt the 0.030" recommendation. I bet you wont notice any difference.