Man Shu… seems the old ways are slowly becoming extinct…. What’s next, the paper manual? Then the actual bike… sad to imagine…
Sneezles61

Ok thanks guys but back to original post.
Trying not to derail things this time.
To OP--my current DT1 "rat bike" has a 32 off a 360 & also a DT1MX piston which is guessing 5mm shorter on the inlet side & is single ring piston. I did notice last time I had the mag cover off that I have a weighted flywheel fitted. I wondered where that flywheel got to lol. Has a brass ring around the perimeter which makes a lazy piston port motor even lazier, but it actually goes like a rocket. I've not had it apart for maybe 30 years but only has occasional use. I've got a std & mx piston so I'll measure the skirt today. I'm pretty sure with the carb I used the 360 spacer but I doubt I opened out where it mates up with the cylinder but might've just blended the step.

You managed 4 wins and 2 seconds that day on DT1. I feel tired thinking about all that racing! And my right wrist may be aching just a bit. Len

Schu you are 100% correct my dad was a photographer and I have Tons of pictures and movies that I’m so thankful for I also have tons of photos and videos of my son. I really like watching the movies of me on my Ht1 and CT2 and my younger brother flat tracking his Jt1 in the cow barn at the fairgrounds every Wednesday night 

I had to go back & read 'that' haha as thought id cropped it out taking a screen shot.

So, back to the thought of shaving a dt1 head.  I should have mentioned squish.  On a modern engine 2 stroke, sized 250cc, I've been instructed in the past to keep it about .050 inch.  That was by a trusted machine shop, technically just one guy that's been doing it for years.  Anyone have a good reference on how to check the squish?  I personally use a piece of .080 solder and check 4 spots on the piston.  I go with the smallest measurement.

Thanks Knutco and RT325, good info. The engine is getting a new DT1MX piston/ring. I'll check squish band after installation. RT325, did you try different lengths on the carb spacer?, if that does anything. Does slotting the stator plate mount holes and advancing the ignition improve performance? I've seen some after market pipes for the RT1 available, helpful or just more noise? Thanks

Personally I'd not slot the stator plate.  If you get more compression, and possibly a more tuned pipe, you'll probably want to retard the timing, rather than advance it.  Even on a stock engine it might be a bad idea to advance the timing more than stock..  If you do some research you'll find these old bikes had alot of timing, vs a newer 2 stroke.  If you need to retard the timing (and you probably should,) that can be achieved by setting the points with a smaller gap.
There are tuned pipes still out there for these bikes, and I'd have to say that will be a big power adder.  But there are alot of shapes and sizes out there, which one is right?  regardless of what pipe you find, it will favor a certain jetting in the carb.  The needle jet/jet needle, main jet, and pilot jet at a minimum will have to be messed with.  Slide-cutaways and air bleeds are also important considerations.  You will easily have the most time invested into tuning the carb and timing, but if you come out successful you will have a good grasp on how it is done.  Maybe I'll try to do a mikuni vm article on what worked for me, a little 101 if it helps.

I used to use electrical resin--'rosin' 'not sure what it is' core solder & go for 1mm-- 40 thou but have ended up less.
Talking mostly 100cc race modified motors when miniature road racing "bucket racing we called it'.
Think i got down to 20 thou but left it at that & didn't blow up--well not immediately haha.
DT1 probably has an overly wide squish from the factory. Be interesting to know what yours has.
Don't take too much out of what i say because my motors might be fast at times but more through luck more than good management & usually have a short fuse.
Wait for someone like "Rich Porting" to come on & give you good info.
One mistake i made for years was only having solder one was so my squish would've been closer than measured.
I'd go through the plug hole & to the edge then turn it over tdc.
Then oneday someone said gotta have it both ways or piston can tilt & give a false reading--which is 'so obvious' haha but dummy me never thought.
I guess there is proper stuff out there to use for squish measuring--put it right around & bolt head down.

Sorry Knutco11 i'm typing before seeing yours & Thumperstew. Getting confuse who started the post.
Back in "69--december "68 on my bosses DT1 when fitting the GYT race kit it said retard the timing to "by memory" 2.9btdc back from 3.2. Only a minor points gap alteration but was the only way to do it then. I 'think' later stators from DT250's up round "77 have a slotted plate to get gap & timing both in the ball park instead of half in half out--if that makes any sense.
Knutco11 you're in control!!.