I forgot to say earlier to consider a fuel issue. Fouling a 300 now days is not that common. Your plug could have gone bad or your fuel is bad are most likely. Not jetting. Also, you say 40:1 but if you oiled that fuel up twice by mistake you’re now at 20:1 (or worse) which will be smokey, spooge running down the muffler. The more oil the run the leaner the fuel mix will be – how lean I don’t know. On the same lines mixing poor quality or ancient oil in with fuel (usually straight into your tank) can also be the cause of too much oil at the bottom of the tank, not enough at the top… I remember with Shell 2SX (still says on the bottle) we had to mix it very carefully or it would not combine well.
I’d be keeping the head as it is making sure there are no protruding dents so hot spots can start issues like preignition, otherwise it’s just cosmetic. From what your saying I don’t think coolant has anything to do here. Replace your reeds, tighten all clamps so they don’t spin but not overtighten, check your airfilter boot/cage for dust/dirt, top end as you wish and measure up how much gap the old rings were. Lift the conrod up and down for any big end up/down play by feel. Take the flywheel/starter cover off and see if you find any white stuff or excessive oil and crap in there. Check the power valve opens and shuts completely easily otherwise there is a pita job right there (more orings and lots of scotchbite).
Nice fresh 95 octane fuel and oil. Never heard of Klotz, US$48 per gallon is cheaper than anything we normally buy here (Mobile1/Motorex/Motul/Silkolene).
As for jetting I don’t know what year you have but I think 2008 – 2013ish are all compatible. I run 38P, 165M, NECJ #3, 1.5ASout for winter. Newer bikes will be different.
