MOPED ARMY

Nice bike, if the bore isnt scored, maybe you just need to clean the rings, ports and pipe to get back some compression.

Hey Rick, congrats on the new addition!

I wanted to give you some information in regards to the compression check that you did. The factory compression ratio on these DTs is very low. I discovered this with a DT400 that I owned some years ago.

Your DT250 came from factory with 6.7:1 compression. https://www.yamaha-enduros.com/index.php/250cc-specs/45-77-80-dt250-d-f-specifications

6.7 x ~14.7 atmospheric pressure should give a reading of approximately 98.5 psi.

In other words, your compression is healthy and spot on! These DTs are somewhat gutless(some of the old timers swear “DT” stands for “De-Tuned”), but still a lot of fun. An expansion chamber/porting/head work might satisfy your want for a little more grunt. The Yamaha-Enduros forum is a tremendous resource for these bikes. https://www.yamaha-enduros.com/index.php/forums

Take care and stay safe!

I owned DT 125, 175 and 250s, underpowered compared to Kawasaki and other brand enduro bikes but more suspension travel especially the late 70s early 80s models so a lot of fun on trails.

At around 16-18 hp it may seem gutless like it needs a rebuild especially if you’re used to riding other Japanese brands of 250 enduros that make more hp but that’s normal. 8k km’s is not that many kilometers so if the piston is not that scored up maybe just put a new set on rings and gaskets on it since you got it apart and run it,

If you don’t have complete air box, filter and rubber snorkel or some dummy drilled holes in it or air box then you need to re jet or replace missing or modded parts to get back lost power

Thanks for the Yamaha Forums link Steve , looks like I have some reading to do .

Ken , the airbox , and everything on else on the bike is original and intact , except the truck clearance light turn signals somebody cobbled on . I don't think anyone's turned a wrench on this thing ever except tires replaced at one point and a shitty Kimpex clutch lever .

Ya oversize piston and overbore is needed. Cylinder ran hot and or lack of oil,

I would let the shop determine what size overbore piston it needs, Don’t just order anyone it may need the second or third size

Nice, I would check crank seals once you are in there, that could have caused the seize in the first place, or do leak down when you're done, but then you're back treating it apart.

I have a 74, yeah it's kinda gutless but it's fun to ride and looks so good, it's one of a very few bikes I would never sell, I've been offered 2600 for it, which is like 7x what I paid!

You didn’t say it. I bet Graham was reading your piston and cylinder. Which, depending on what your definition of “seized” is, looks like they got intimate with one another at some point.

Haha yeah! In my neck of the woods we call that a seize, either way it happened for a reason.

You see these listed for crazy prices but I don't think they sell, you can get them for a couple hundred bucks pretty easy yet. The monoshock ones don't pull the tail the way that the older ones do, but they are all going to be going up in value. My buddy from Japan said they have caught on over there and a clean dual shock or DT1/2/3 can see 5 figures.