Time for a new project.
I brought this DT250 a few months ago and have had it in the shed while I finished my GT185 cafe racer.
Looks like it is a 1974 DT250A. Picked it up for $650 which is probably a too much for what I ended up with. Anyhow, its pretty complete, the engine turns over & has spark.

I want to turn this into a tracker, as per the reference image. A bare bones bike with nothing on it that it doesn't need. Will be road registered and I plan to ride it regularly.

The current plan-
Must handle well, stop well and be fun to ride
Must look the part
Front end swap with disc brake and better forks
19" wheels
Change from 6v to 12v
Tracker seat
Powder coat frame
Polish and paint

I have been working on this bike over the last few weeks. Spark is in consistent and the top end was worse for ware. The bike came with a spare engine so I pulled off the top end to find a good piston and clean bore.
1 good engine from 2 could work here. I ordered new gaskets and a new coil. Parts are in and started reassembly. Noticed that the positions are actually different. The top ring and above the ring.
Regardless the top end went back together alright until I tried to install the reeds and manifold and found that they are too big for the cylinder.
Closer inspection shows that the cylinders from the 2 engines are different. Both of the engines show numbers matching 1974 model.
Does anyone know how I can tell what cylinder I have?

Looks like a non-USA model? And might be an optical illusion but pistons look quite a bit different in size rather that one just having the dykes top ring and the other having the keystone (probably... could be conventional) top ring?

Anyway, Yamaha usually had a model code number cast into the cylinder... I think on that model it was at the bottom across where the transfer port meets case on right side? Could be around the reed area. Should be 3 numbers or maybe 4 or 5 numbers and letters. Not to be confused with the engine displacement (i.e "249cc") which is also often cast into the area where the transfer port/case join.

Took a look on ebay and could not find a good picture of a 74 cylinder showing he model code.. did find that my memory is flawed on the location of the number.

Here is an example of the type of number you are looking for... this is a 77 with a "1M100" cast into it. Hopefully you can find something similar on yours.

I am not sure exactly the difference, but it could be an MX360 cylinder. They will interchange in the case if I recall correctly. If from 73-74.

The 73 MX’s got that new Case architecture a year before the DT.

Here are pic's of the R&L sides of a USA 1974 DT250A. The numbers are clearly shown.

Thanks for all your help. I would suggest this is an Australian delivered model due to being in Australia, but we do have imports here as well. I have not measured the pistons yet but they look the same size with close inspection. Picture below of the cylinder shows the code. Looks like 1M100. Also the engine number it came off 450-029457.
With a 40+ year old bike this cylinder may not be the one delivered from the factory!

Pics

The cylinder the bike had on it has a code of 43800

The 1M1 jug is off a DT250D 1977 , , the difference in the reed block intake , will be smaller on the later model, just like the 1M2 [DT400mx] is smaller than twinshock DT400b. it was a downtune on the later models, for emissions ,etc,