One more sparkplug question

[Thumpbass]

I have a '79 100hp Johnson (100tlr79s)...the original repair manual says I need Champion plugs, L77J4 with a 0.040" gap but I have seen posts here that suggest using a QL77J4 with a 0.030" gap on similar motors (year and HP not exactly the same but V-4 motor around the same age). I'm trying to figure out which plug and gap I need considering what I've read here and a note I read in the West Marine catalog that basically said that newer plugs had changed due to fuel changes over the years and you should buy plugs according to the new standards. To make a long story short, what plugs do I need to put in this motor? And how should they be gapped?

 

[Walker]

Re: One more sparkplug question

The plugs are the same except that the QL is a resistor plug. Cuts out interference you might get to any accessories like radios, fishfinders etc. Use either one.
If your manual says .040 gap then that's probably what you want to gap them at. Or try .030.
Those plugs are available at most ayto parts and even some Wal Marts carry them for around $1.70

 

[Thumpbass]

Re: One more sparkplug question

So what would happen if I gapped them at .030? Would I gain anything or risk doing any damage to the motor? I replaced the plugs because the motor was missing (coughing) pretty bad at idle. I since replaced the plugs and gapped them at .040....the "missing" problem got much better but it still sounds like it's missing a little. I can't really tell if it's still a "problem" or just a 27 year-old 2 stroke motor. So there again, would gapping the plugs at .030 possibly clear the missing up even more (or completely) but at the same time put me at risk for engine damage. Thanks in advance...I'm just handy enough to blow stuff up:%

 

[DJ]

Re: One more sparkplug question

The original plugs (Champions) were spec'd with a gap of .030"

It has been found that a gap of .040", ON A HEALTHY ENGINE ran better, at idle, than the .030".

If you have fuel delivery issues, all bets are off.

 

[jtexas]

Re: One more sparkplug question

dj is that just the V-4's or would you say the same about the triples of that same vintage?

thanks!