[graysilm]

I was wondering what the right plug is for this engine. According to clymers, I need champion L77J4. Nobody has this plug, and when I go to champions website they don't have this plug. When I type in my engine criteria they show me L77JC4. According to champions website, I need to gap the plug to .30, however clymers says to gap it to .40. Does anyone know what is the correct thing to do? Thanks.

[F_R]

L77JC4 replaces L77J4. The C means copper electrode, a Champion "thing" You can also use QL77JC4 which has an inductive radio interference suppressor. I always used to gap them at .040 but others seem to be cutting it down to .030 or .035. Whatever.

[graysilm]

what would be the effect of using a smaller gap? I don't understand how there is a descrepancy in this gap thing.

[F_R]

The gap affects the actual spark voltage. The closer the gap, the less the firing voltage. That is because the voltage rises until it is high enough to jump the gap, and then that's the end of it. That happens extremely quickly, but it does take a certain amount of time. So, with that in mind, an ignition system that is a tad weak can fire a closer gap, but not not have enough available voltage buildup to fire a wider gap. However, a wider gap and higher voltage ignites the fuel better. So you have a balancing act. Heck, set them at .035" and forget it.

[graysilm]

thank you