It makes a massive difference in 2 stroke motors with hand mixing of gas and oil.

I can now troll all day at the slowest & smoothest speeds in gear.  Plug white insulator is CLEAN with no burnt oil or wetness.

I index spark plugs in just about everything.  Any motor that has a spark plug will run better if they are indexed.  

I did not know that all Evinrude  E TEC motors must have all plugs indexed to face the fuel injectors...........Probably due to super lean fuel mixtures of F I engines. Read long ago.  Some new engine will NOT EVEN START if plugs are not indexed........... That will drive DIY guys to a dealer for sure if they pull the plugs. Then it barely starts with new plugs. 

Above a fast idle indexing does almost nothing.

I didn't even know this was a thing!  But it makes sense to me, and since it's free to try, I will be doing this from now on.  Thanks guys!  

The DFI Evinrudes are subject to plug fouling if idled or run at very low RPM much from the sot created at idle.  If not indexed, the ground tip creates a shield and lets it build up on the plug and causing it to carbon foul.  

 

By the way, it's not exactly free.  You either have to have different thickness seal rings or extra spark plugs you can switch around until you get enough plugs indexed properly.

Being an old racer indexing plugs is normal procedure. You also need to tighten/torque plugs correctly and requires sets of seal rings or lots of spare new plugs. Don’t cheat on torque!    

Tom 

Old racer here too.  I always indexed them in my 2 stroke.  I haven't touched the plugs in my 4 stroke, but they'll be indexed when I do.   

I would not recommend doing sparkplug changes with a HOT , just stopped engine.. Hot Aluminum strips the threads a LITTLE easier.

I bough 4 more NGK plugs that are 1 heat range hotter than normal. Lady Tech person said said 2 steps hotter can do slow damage if run WOT too much time.. Happy with no oil on plug threads. Have run & marked 4 of the 6 plugs. I run 50 to 1 oil mixture in the main tank. 100 to 1 in the 5 gallon TROLLING  tank. ONLY !! Quick connect plugs make it simple.

 

 Will check out what the SCUBA guys are seeing in the area.

Never change a spark plug in a hot aluminum head and "ALWAYS" put anti-seize on the threads