Hi Guys, been a while since I have posted and have been meaning to get back to you about how my 220 is after taking then 0.5mm off the head.... it goes great. in combination with the heavier clutch springs adds a lot more grunt, great for lauching over logs ditches etc climbs in the rev range alot quicker and pulls longer.....just completed the 4 round south island cross country series on it. ran mint for all the 3 hour races- just the rider slowing things down!
back to the old questions I run race gas becaus it is not that much more expensive than pump, is more reliable and smells better. When I can't get it the KDX will happily run on 95 octane, I still run it with full synthetic oil at 40:1, the higher compression does not cause any problems.
my 2cents on what has been discussed.. I have played with timing with very little effect on performance, best to just leave it in the middle.
I had a browse throught the technical stuff on cyclinder head machining and I think that if you only took 1.1mm off you will still have the lip around the edge of the head so have not gone too small on the outer area of the squish band and have not touched
the squish angle at all.
I can't see why your bike would not run normal pump gas, as I have siad the guys I know took 1.5mm off the heads were still running pump gas.
changing to a 50:1 oil mix adds a bit of an unknown into the equation, I would initially go back to standard 32:1 and work from there.
My gut feeling is that you might be getting way too lean on the main jet which is giving you the nasty noises you are at WOT, and if you are getting to WOT 50:1 mix is well light on oil. it may be fine for lugging along a trail ride or getting through tight trees so that you don't get spooge and fouled plugs but IMO you are risking a whole lot if you are going to get on the gas properly.