Indeed I accept that my actions can and most likely will lead to failure -- if pushed too far -- and too far comes pretty darned quick if not paying extremely close attention, which I am, I hope... I also take into account the advanced age and wear on this engine and go to great lengths to listen carefully to what it is telling me. I was simply hoping to mine the brainpower here for opinions on whether or not higher octane fuels allow a slight increase in timing advance with these particular engines. (L3) I confess that for years I accepted such a thing as holy-writ, but lately have seen much that explodes the octane/timing theory as myth. I remain open to facts but so far my tests show a small boost might be gained with 94 or better fuel, but without proper testing/analyzing equipment my results are highly anecdotal and possibly even wildly inaccurate. I now tend to think it is the physical design of the pistons and head with contributions from engine management systems that govern allowable timing settings and a few points more octane only just marginally bend the curve, so to speak. Again, I was simply seeking opinions from folks well established in the outboard world.
And yes, I simply switch the key off at speed and release the gears before "reading" the plugs and only after at least 5 minutes or more at wot. I use 3 sets of plugs and wash them in lacquer thinner before such testing. I typically run BUZHW-2 plugs but for reading I have been using BZ7HS-10's gapped at 40 thou. "Tan" is perhaps a bit generous and brown or dark tan a better descriptor as to the general state of the electrodes etc. The insulator near the centre electrode is at worst tan in colour but when I read a plug for fuel burn I am looking at the base of the insulation with a lighted magnifier. I am still getting a smallish amount of black carbon on the ground electrode and shell face but that might be down to the chemistry of the oil. Castrol "Super" Outboard Plus oil it is.
edit: I will include here the obligatory disclaimer: DO NOT TRY THIS AT HOME! All stunts performed by a psychotic tinkerer in a closed shop and an abandoned lake. Avoid contact with skin and always wash your hands after going pee-pee. Results will vary. Do not eat or place in mouth for any reason and wear protective clothing, especially a hi-vis yellow jacket with reflectors on it. Maybe even a flashing red light. Just don't do it!
