spark plug question
 

I've been using Champion UL77V gapless plugs in my 1986 evinrude 150 for years, I've found that they've been harder to come by ,and when running a cross reference on my motor it says to use Champion QL77JC4 which has a gap.I remember looking at the shop manual and it said to use the UL77V, but I also remember a few years back a local boat mechanic said use the JC4's.
Any suggestions, or opinions?.I guess the gapped plugs might run smoother at idle.

found this chart,not sure if it helps or not.

http://continuouswave.com/whaler/ref...gChart2008.pdf

i have always heard non gapped(surface gapped) are for high speed running and gapped were for slower speed idling

OMC released a bulletin back in the early 90's to supercede teh surface gap plugs to the QL77JC4 gapped plugs due to the tendancy of surface gap plugs to foul out during extended idling. If you're after max performance and run at sustained high RPM's(5K+ RPM's) stay with the UL77V surface gap plugs, otherwise switch over to the QL77JC4's and enjoy better idling and low RPM performance. I avoid the QL78YC's though as I have found teh extended electrode plug to not perform as well down low.

Thanks, I rarely ever run at 5000+, and the idle is a little rough so maybe I'll give the JC4's a shot and see how she runs.

Damn, I just put QL78YC's in yesterday. 1999 Johnson 175. What should I have gone with?

-Svence

The QL78YC's will work fine, but they do tend to foul a bit easier than the QL77JC4's do at idle and trolling speeds. I know the QL77JC4's are getting harder to find though.