@Knutco11

I did try the MX head a while back, when the DT was pretty close to stock.  Way too much compression.  The MX360 exhaust port is much higher than the DT which means less trapped volume after the port closes, so the combustion chamber volume is correspondingly smaller.  If I had some 110 octane it might have been alright but on pump gas it was pinging constantly.  High compression just doesn't mix well with air cooled big bores.

Ok thanks guys.  Goes to show how retarded I am.

You're not "retarded".  I appreciate that you validated my theory that the artificially low "trapped" compression ratios the Japanese published for two strokes made people think they needed to raise the compression.

Octane is another "apples and oranges" topic in the USA since the rating method has changed since these bikes were new.

Heck, same thing happens with language...  if you read books written a century or two ago, some of the words used then are either not used today, are considered "offensive" today, and/or perhaps have a COMPLETELY different meaning today.  For example calling someone "nice" a couple hundred years ago used to mean you were calling them "foolish"...  which certainly was not a very nice thing to say! 

Or back in the early 1900's the color pink was considered more "masculine" and was used for baby boys while the color blue was considered "feminine" and used for baby girls.  Somehow those stereotypical color meanings got swapped in just a few decades.

Not just time... even countries and cultures assign different meaning.  I didn't understand why a female friend of mine visiting from London was offended when I suggested a fanny pack for a hike we had planned... until she explained what "fanny" means in the UK.

Yes RON/MON ratio is best if tight. GO FOR MON.

118/130 av gas
89/98 premium in US
80/92 in mexico

Most is BS.
Av gas is/was 118MON. 130 boosted.
89/98 is watered down with CH2OH
80/92 is just junk

Indolene RED 120MON was best ever.

CLEAR indolene was unleaded 100MON


cliff

The comment about pink and blue is interesting.  I remember my class in high school.  The "macho" dudes wore pink to prove how tuff and how much they didn't care about it.  I always found that kinda stuff to be too much.  Still see that plenty today. It's all in how you wear it I guess, lol.  Guy could be wearing a faded red shirt, that looks pink.  He still looks like a regular heterosexual male to me.  And the color of a womens clothing does not make her any more, or any less attractive, imo. I personally don't think there is much normal about anything.  To try to fit into the "normal" mold just doesn't do it for me.  We are all our own individual.  But yeah it is imprinted on the brain.  Not so much for women wearing blue, but to see a male intentionally wearing pink, you almost have to question it by today's standards.

Going back to the original question, any fairly modern production stock Yamaha, will, at most, require a "premium" 91 octane fuel by USA standards. Personally, if I was worried, I'd get non-ethanol fuel as my first priority, regardless of the octane rating, because it's predictable over time, while the ethanol fuel, regardless of original octane, is pulling in moisture over time and does degrade. Even the rather dated kx100 produces 26hp at the rear wheel on premium. That said, the jetting and timing on the mid 70's bikes was a lot worse than anything in the last decade and might reward the use of race fuel.

Then on a random tangent, as I've gotten into snowmobiles over the last few years, as fuel injection became common in the early 90s, with the onset of ethanol fuels, the machines came with a wire you'd disconnect if you only had ethanol fuel available, to make them run ~10% richer. 10% richer for 10% ethanol, interesting. Granted, a snow machine might get asked to run at -10 degrees at sea level, a very oxygen rich environment requiring a rich mixture most motorcycles will never see.

Now Yamaha specific, while the real need for hp was pretty much plateaued for street bikes, it's incredible to see their 998cc three cylinder engine in snowmobiles coming out in stock form at 200hp, but getting a basic reflash to 270hp with aftermarket intake/exhaust on 91 octane pump gas. People running race fuel on the engine have pushed it over 400hp. Which one might wonder why it's needed until you take a look at what people are doing it them;

Which in my mind is crazy as turbo two stroke 850 engines are producing 180hp most of the time, to produce double in a slightly larger four stroke, kudos to the Yamaha engineers!

Awesome video snowmobiles are fun

I have a love hate relationship with snowmobiles. Lots of fun when right, but I can only count on one hand the amount of trips people weren't breaking down. Then my fun trip turns into helping people fix, lol.

I'm with you on the love hate relationship, it makes me appreciate the reliability of my '72 Yamaha Enduro all that much more

My last snowmobile was a 73 Chaparral SSX liquid cooled 340. Yes liquid cooled back in 73. I sold it about 10 years ago and it still looked like new. I assumed modern sleds were very dependable compared to the 70s sleds.