One of the cool things about EFI is the ability to run lean, which makes the engines and plugs last longer. It goes richer for Start cycle on all EFI units, then switches to match throttle requirements. I did something similar with my carb'd Fairmont Ford when I rebuilt it in 1995 (1 bbl Holley) with a re-cal, have now received over 375k miles from it. When a freeze plug cracked last winter and I pulled the head (thought it was a blown head gasket!) I was astonished to see NO ring ridge in the engine, whatsoever. Amazing how running it at 16:1 can do that...the valves are in perfect condition, too, and the temperature gauge runs half of what it did when at factory calibration. And the MPG went up from the factory 14 to 18 in town, and from 16 to 20+ on hiway, at the same time (and of course it climbs high mountains easier). I'm about to try this with my 750 this winter, switching to a leaner-burn setup to see how it does next season. I'm going to try for 16:1 above 2500 RPM (it needs more like 12:1 to start and idle well, though).
you aren't worried about the barrier layer and burning a hole in the piston?
EFI's consistency is what made running leaner possible. Carbs are really crude as measuring and metering devices when you really think about them. Bringing this back to our points vs electronic spark that's the benefit - consistency over life of component that contributes to longevity.
My GTO ate through 2 packs of plugs a year, my EFI jeep has had the same plugs in it since 2005. My Dyna S CB750 has had the same plugs in it since 2009. I'd change them but why? they still work fine.
No, I'm not concerned about that, at least not like Honda Warranty was in the 1970s. The gas today is far more consistent than it was back then. We used to see stuff like bromide and lead accumulating on the plugs when rich, shorting the plugs entirely. Now, it is just the occasional overly rich mixture that collects carbon on them, to short the spark out. This stuff cleans off easily with a sandblast o even wire brush, in most cases. But, the slow burn speed of ethanol-laced and ethanol-accepting fuel mixes today acts as if it is higher octane when it is not, and if the carbs are set to normal 1970s mix rates (like 12:1 A/F below 2000 RPM), the plugs get wet during heavy traffic idling. If you don't then get a change to immediately blow them clean with a high RPM blast, they slowly foul with the carbon. It doesn't much matter which kind of ignition the bike has then: the wetness and carbon stay on the plug and foul the tips. A good example is my own commuting: if I stay on the freeways I can ride all summer on the same set of plugs (I change them at every season, clean them, and put the old set in the tail trunk for the next year), but if I get stuck on the surface streets in typical Denver traffic, it can idle 20 minutes on a 30-minute commute, and the plugs will foul after a few weeks of this riding. The idle circuit is easily adjusted to stop this with the air screw, set to 3/4 turn instead of 1 turn to lean it out, but the off-idle-to-2500 RPM range is too wet (5-to-20 MPH in 1st gear stuff) and this slowly loads the plugs up wet. Dropping the needle or lowering the float levels can help here, but then the mainjet must go up a bit for the midrange comp, and then you're pulling the carbs to do it. Painful stuff then! So, it becomes an off-season project, lest the nice days get away.
These engines can run at 20:1 A/F mixture with today's fuels, as they are knock-resistant in order to cope with auto EFI systems, which can be slow to respond to sudden driver's foot requests. This was not the case when they were first designed, so the carbs were set conservatively rich to prevent warranty claims: sparkplug replacements were cheap as compared to pistons. And yes, you can get more torque with richer mixtures, a racer's favorite carb tweak - but racers go to the track with boxes of sparkplugs handy!
