I forget exactly what size it is but one of the mikuni 500 series main jets is
actually leaner than a 400 series jet but I think it was a 510 there was a
lengthy article about this but I cant find it, when you change jets just make
sure you verify what it actually does.
Your discription of your plug sounds plenty safe to me but something is going
on to make your
Engine diesel, if it is a intermittent air leak a plug or even a
EGT reading might not happen fast enough for you to save your Engine, a
seizure because of improper jetting when your checking your jetting as you
are wont happen as unexpected. you really gotta screw up. all that being said
what is the history of this Engine what mods has been done to this Engine.
You can spray around the Engine while its running but your not going to
check the seals that way simply because they are not accessible to spray
whilst the Engine is running, that is a generic statement that is used through
out the Engine trouble shooting industry and really does not apply to this
Engine, when I am looking for a vacuum leak I like the pressure test and
looking for oil spots, most Engine leaks will have some sort of trace evidence
where the leak is in this case oil will be found where it is leaking even if it is
just a slight amount like equivalent to one drop mixed with some dust stuck
to your Engine cases, if you see something like that you need to be suspect
and take a closer look, I would not want to wash off that evidence with carb
cleaner I would want to make the visual observation first, I wouldn't want to
wipe off something dirty on your Engine with a rag either without first looking
close you need to get into the detective mode (CSI) looking for little clues...
I cut my plugs apart by putting them into a lathe and turning down the area
where they crimp it together I have never done it any other way, I have
seen plugs where they used a hack saw to cut the side of the threads off,
if I were going to try a new process for the first time I would use another
plug first once you master the process then attack the plug your trying to
read no use destroying the evidence your trying to see during practice hehe
Let us know what you find you have a unique problem cant wait to see what
is actually causing it.