Steve, I know you don't make things up but I heard quite different from what you said about 32:1 being the maximum amount of oil to use.
Here are my guidelines with the belief that more is better protection without interference of ignition:
standard mineral oil 20:1
semi-synthetic 25:1
full synthetic 30:1
Gordon Jenning wrote a ground breaking article back in the late 70s about oil mixture:
http://www.bridgestonemotorcycle.com/documents/oilpremix6.pdf
We followed this like a religion back then in the era of cast iron sleeves and before power valves.
This information is accurate for castor oil, which was the go to back then for maximum scuff resistance.
The 50:1 oils back then were only designed for low powered engines, fouling resistance and smoke resistance.
I ran a CR250 and a 340TNT sled and didn't go anywhere without a pocket full of plugs and a wrench.
In 2000 I bought a KTM 125EXC that called for synthetic oil at 40:1.
Since I still kept a spare plug and wrench, I ran that plug for YEARS, before it fouled.
Wow. Since then I have switched to 50:1 and usually run Motul or Ipone. After 7 years of use the head looked like new.
The synthetic stays fluid and doesn't soot up and stick, which is why it is used for powervalve engines. It is self cleaning.
7 years and my nikasil cylinder and piston was still in amazing shape, no scuffing, little wear.
I did try other oils in the KTM and found oil is an important component of low rpm ring sealing and cheap oils (and injector oils) don't cut it. Top of the line synthetic pre-mix oils are the only ones that deliver ring sealing and foul resistance.
These engines are different. Thin chrome bore. Where to start? I followed the manufacturer's recommendation. 16:1
What a mess! Oil dripping out of the pipe, hard starting and very soon fouled plug. No surprise, even at 20:1.
I gradually thinned the oil (and wrote about it on these forums). 40:1 gave a noticeable lack of low speed ring sealing so I settled on 32:1. Bike performs the same as on 24:1 without the oil dripping from the pipe. I have been jumping around with synthetic, semi-syn and conventional oils, using up the various gallons we have in the shop and seeing what the results are for performance and carboning. All seem to work better at 32:1 than 40:1, even the synthetic, probably due to loose tolerances.
Here is the latest look at the head off with an unknown 32:1 semi-synthetic (was put in an Ipone measure bottle years ago) I am using up:
It is a soft sticky wet soot. It wiped off the polished sections well, but not the cast areas:
It has been hard breaking the mould of what I think I know and what I have read and believed for many years. That is why I am testing all I can again with these engines, to challenge what I think I know, is it true?
Steve