Interesting, good info. Again, my goal is a modest power improvement with near stock reliability/rideability, not an explosive racer. I may still try the DT2MX head, but will try cc'ing both stock/DT2MX for comparison. I don't plan to work the cylinder beyond removing gross casting protrusions and light port matching(intake manifold side). This is at the bottom of my list.
In a different area, what are thoughts on aluminum rims or different wheels? I want 19"/18" wheels and like to reduce weight. Also, the stock DT1 rear sprocket is hard to find and expensive. Thoughts, suggestions, warnings? Sorry for the subject drift, maybe I'll ask this in a different post.
Thanks

I think we are more on the same page than we realize, markt.  I do not claim to be any sort of engine builder, I have just had luck enough to make some stuff work.  It's hard to compare a 2 stroke and a 4 stroke, so I'm going to refrain from doing that anymore.  I will boil it down to this.  I see low compression figures on the stock enduro motors, and I have tried an rt1mx head on a rt3 with good results.  It did gain power everywhere, but most notably was the lower rpm torque increase.  I will leave it at that.

Haven't looked for sprockets recently, only suggestion would be to keep it close to your original size.  The wide ratio enduro transmissions are a best of both worlds kinda thing, and the 1st and 2nd gears get weirdly spaced if you gear them too low.  I tried a 14,15, and 16 tooth sprocket, and 39, 47, and 53 rear sprockets.  Ultimately went back to the stock 15/39 setup.  You'll wanna see what size they had stock.

I know MarkT & others are right regarding comp ratios.
So my story only related to 'me' & my DT2.
Just talking a bit of rubbish here but in "72 when my DT2 arrived as a fill in until the proper race DT2MX got here--i fitted a DT1GYT kit head to the std DT2 cylinder & ran it on methanol with a chamber exhaust.
It actualy went like hell & revved crazy too.
Can't remember if i used a bigger carb but recal the annodised original slide sticking bad on cold days & at that stage was running shell M oil through the pump which bypassed the carb.
So started mixing it in the methanol & cured that problem except i found on cold days again that the mix went milky.
Think [what was it] accetone or something sorted it.
There's a video up here somewhere of that bike in a fleeting glimps but that's getting off the subject so won't bore you lol.

Knutco11,
Sorry, but we're not even close as once again you've said you "see low compression figures on the stock enduro motors". 
My point is Yamaha compression figures are NOT low because it's an apples and oranges comparison.  No different than someone saying it's cold outside when someone says it's 40 degrees without caring that they're using the centigrade scale (40 C is about 104 degrees F)

A compression ratio of 6.8 to 1 is not "low" when it is measured from exhaust port closing (two stroke) or when measured from intake valve closing (four stroke).

I have a OEM YAMAHA steel 45 tooth DT1 rear sprocket on eBay. It’s not cheap with the 68’ DT1 stock size is 44 tooth. They’re difficult to obtain in good condition in steel. Aluminum is easy.

asco

I still think that's low.  6.8 to 1 compression dynamic (advertised duration when the intake valve closes) on a 4 stroke, is low.  Maybe that's a liquid cooled v8 way of thinking, but it has worked for me.  Lol.  8 to 1 dynamic with cast iron heads is what I target, to be able to run pump fuel.  Usually come out about 160 psi cranking compression.  I remember early years of jamming big cams in otherwise stock motors.  It's not cool when at the end of the day, your slower.  Lol. 

Now that I'm thoroughly mixed up on 2 and 4 strokes again, I gotta wonder:  how do I get away with running pump fuel in my old 360?  If the rt1mx exhaust port timing is the same as an enduro cylinder, shouldn't it be a ping king from hell?  If like you say, the stock enduro's are already high compression?

In my experience no 4 stroke advertised compression from the vehicle manufacturer is measured from intake valve closing, at least during my lifetime.  That's a system only used by some two stroke manufacturers.  6.8:1 from intake valve closing would probably be at least 9:1 from BDC...  and that's what the 4 stroke spec will say, 9:1.

Two strokes are very tolerant of lower octane and there are so many unknowns.  Biggest one is are you sure you have an unmolested MX head?  So many sellers mislabel parts.  I've tried MX heads on stock Enduros and it has never worked out well.  I don't remember hearing actual pinging but the performance testing definitely showed a loss of power.  Measured top speed and acceleration both suffered.  BUT, as I said, there was a "seat of the pants" boost in torque at lower RPM.  Felt stronger, but stopwatch and side by side testing showed a performance loss... especially after a good warm up.  Temps were definitely higher with the MX heads.  I have never tried this with an RT2.

I'm glad whatever you did is working for you.  That's all that matters. 

 

I know if I put the rt2mx head onto rt3 cylinder, and try to kick start it, it really hurts.  Hurts just thinking about it...

Perhaps it's not an rt1mx head.  I was initially just looking for an rt1mx head, but I found the head and jug as a set.  The cylinder is cut cleanly for the rt1mx pipe, and it definitely has ports that are polished, or blended.  The spark plug angle is much more upright in the "rt1mx" head, and it's obviously smaller chamber than stock enduro head.  But not as small as the rt2mx chamber.

Stock RT2 head volume is 48cc so compression ratio comes out to about 8.3 to 1 using the normal method vs the "advertised" 6.3 to 1 using the confusion creating "trapped" method that Yamaha and others used only for two strokes as far as I know. 

I've always wondered if there was some sort of tax on two stroke compression ratio in Japan?  Like some countries tax displacement or rated HP which sometimes resulted in a manufacturer underrating HP for example.  That's the only thing that makes sense when Euro bikes were advertising much higher compression ratios...  when we were kids we thought the Euro bikes HAD to be better/faster because the Japanese bikes had much lower compression ratio specs!  If there was no good reason to use a non-standard method, it sure was a dumb marketing move.  I think it was when I read Jenning's Two Stroke Tuner's Handbook in about 1975 that I learned why the numbers were so much lower for Japanese bikes.