With the very cool weather last week I decided to do some "speed runs" with my
new prop. Engine ran strong, air temp was way under 60 degrees, and I made
several passes with two props. I run NGK BPR6FS plugs. I had never had the chance
to make runs with the air temp as cool as last week. When I switched from the
normal AC MR43T plugs to the NGK's the engine seemed to run cleaner. At least it
smelled cleaner to me so I continued to use them although I don't think the engine
ran any better. When I pulled the plugs for my winterizing routine the plugs looked
like new. I put about 35 hours on the boat this year and thought there should be
more color to the plugs. So did the extra cool air make me more efficient or lean?
I did a lot of research the past few days on "spark plug reading" and am more
confused now than before. When can you determine you are lean and not just
running well aside from when something melts? My engine is a stock Merc 502 MPI
with 325 hours.

If that engine is stock, your not gonna run it lean. Those ole Mercs will run forever.

If the insulator is white that means it is leaning out. There should at least be some tan color.

Should have a little color...20 hrs on this one.

Tan is good, black is rich, peppered is BAD (LEAN).

X2

hi all at offshore been tryin to find best plugs for 2001 496ho ,denso TJ 14-R-P15 is on the E/cover these are plattinam allso this #came up IT 16 these are iridium would these be beter or is there a eqiv like ngk/ ac delco ???? as denso plugs are hard to get here in england the TJ # which is on e/cover is the same plug used in H/duty 3500 chevy truck tried to cross reff but no luck any one used other plugs thanks all at offshore only paul from england 9 bucks a gallon

I thought I'd post a few pictures of my plugs for reference sake. When
looking at the used plugs it was very difficult for me to see an
appreciable color change on the porcelain. However when I looked at
the used plugs next to a new plug the color difference was very apparent.
I did notice that all 8 plugs were clean on one side and had a soot/burn
mark on the other. 4 plugs had the soot spot on the front with the ground
strap opening to the right and 4 plugs had the spot on the front with the
ground strap opening to the left. Does that correspond to the even and
odd banks? Or is it just a coincidence? Do these plugs look good?

Run it like ya stole it BIG Daddy ,its all good

The darker spot is probably caused by how the the plug is sitting/rotated in the hole.
Those plugs look fine. I look more at the color on the base circle than the color on the porcelain.