haha! good to know. Its not that i don't believe he ran a 17tooth, just trying to verify its possible on mine. I was referencing Partszilla and dennis kirk which both list a 15 tooth as being OEM with a yamaha part number and dont list any 17 tooth as being available, only 13-16 tooth. Amazon shows china 17 tooth units that "fit" a CT but when i looked at mine the chain looked very close to everything around it with the 16tooth that is on it currently. 

Thank you so much Mark for your kind words. Yes my CT3 ran very well! Unfortunately, my riding days are over due to my aging body (I am now 79 looking at 80 in a few months) and to be very honest, I REALLY MISS THOSE WONDERFUL YEARS OF THRILLS .  However, I have been working on Yamaha’s and enjoy doing so . A few months ago I sold my beloved CT3 to forum member RickC for a favorable price along with my old 1965 Honda 305 Superhawk. I feel very good knowing my bikes went to a very, very good home.

Like Dogboy said I would have checked the sprockets to see if they were stock. As for my DT125 it does need to be in the band but it will ride in 6th but does loose power in wind and on hills but that said it belts along. That's one of the reasons I like the heaver xl250 as it's way easier to ride on pavement (and has a much better seat) , but once off road these old 2T are insane fun!

Took it out for 70 miles today. Being more prepared for the power delivery this time it did fine. Down shifting sooner, keeping it at 6-7500rpm was able to maintain 48-50 up hills with a headwind. It’s CRAZY how much just a head wind effects it, wouldn’t even pull 5th on one flat section but the head wind was blowing me around all over. Felt like I was doing 80mph when I was only doing 50
Still curious what the milled head would do but I’m in no rush to do that. It’s good enough!


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I would not mill the head.  Or raise the compression unless it's to restore compression after porting the cylinder (raising the exhaust port reduces the "trapped" volume)

For some inscrutable reason, the Japanese decided to spec two stroke compression based on "trapped volume" after the ports close instead of using the conventional method of using the volume with piston at BDC.  

(Four stroke exhaust valves often close after BDC but nobody lists the compression spec based on "trapped volume" after the exhaust valve closes)

So what looks like a "low compression ratio" on the spec sheet is actually around 11:1 if you measure from BDC.

Stock head is not the thickest or strongest casting.  It's much better to mill the cylinder deck as DVM suggested as piston usually stops lower than the top of cylinder.  Plus "squish clearance" is important and cylinder milling is often needed to optimize.