Which one would you take ?
Dont forget to check my previous comment on the last page.

I would take the Yamaha, but I am not all that objective. For one thing, the Yamaha has the Monoshock supension which makes the bike a lot more rideable in lots of situations. (Note I own both the mono and twin shock versions of the 400 which will ride the same, albeit with more power).

If you have access to that Suzuki in that condition, it would be hard to say no depending on the price. Still - if the condition were comparable to the Yamaha, I would take the Yamaha in a heart beat.

In my experience the best thing to do first before tearing down an engine is to pressure test the crankcase...

And just curious if you ever checked which groove the clip is in on the slide needle? Or if you tried to change it?

A stock 1978 DT250 is not going to run with a later model RM or YZ250... but it should run pretty good.

My 1979 DT175 goes 55-60 mph pretty easy and I've had it up to a little over 70 on the El Mirage dry lake bed... so a 250 of that era should do even better...

One other thing can be a problem is the speedo itself... I had an 1975 RD350 with really low miles on it that read slow 20 mph! At 50 mph indicated I was really doing 70! (Verified the speedo was off with a GPS clamped to the handlebars The inside of the almost new-looking speedo was gummed up and worked fine again after a careful clean and lube.) It's probably not your problem but something to check if you have stock gearing and the speedo is not indicating as fast as it should at redline in top gear.

I posted these pictures because i was looking for a TS250 when i bought the DT.
As you probably already know im a Suzuki guy.
A few years ago i was convinced i would never own a yamaha :p
But sadly i couldnt find a TS in quebec.
So i got the next best thing (in my opinion)

I never checked the needle because i dont have any time to work on the bike these days.
As soon as i have spare time im going to check that.
Im going to check if the speedo is correct as well.
I have yet to check the gearing too.

Ive never run a leak down test on a 2 stroke before but i think ill do it for this bike.
I generally thrust my experience with 2 stroke bikes, but ive got no experience with this old machines so i cant compare it to other bikes ive worked on.
What i mean is i dont know for sure if it runs good or not.
Normally i just try the bike and i know the problem, but for this one , since it runs ''good'' to me, its hard to tell.

Ive never seen a bike that runs ''good'' and that is down on power like this one.
Generally the newer bikes lag or they missfire or they run bad when they are down on power, but this one seem to run perfectly.
Although im pretty sure its down on power.

Would I have to choose one of the two? I don't like either one of them, if we were back in 1978 and those were my choices for a new bike I'd wonder over to the used department and try to find a 1973 or at least a 1975 at the latest.

A few months ago you asked about exhaust pipe cleaning. I am a little suspicious on your exhaust. At low RPM's you would not notice it as much, but at higher RPM it would. It could be clogged up with carbon or mouse nest. This model already has a choked exhaust.

Could you elaborate on this if you please. Id like to know why you wouldnt own my bike ?

Yes indeed, with the great help of this forum, i was able to find that my exhaust is cloged.
Since then, i wasnt able to clear it so i dont run a muffler right now.
Without a muffler, the bike as more power, but still, i think there is more power to be found in this engine.
I wasnt able to see if the expansion chamber is cloger though.
The expansion chamber does have a small crack.

EN, Meis, or experienced engine builder may have some comments on this, I am not an experienced engine builder:

I think we found your problem. If your bike is running better with no pipe, then it should run even better with a clean, free flowing exhaust. The 78 DT 400 top speed is 85 MPH. So why is your DT 250 only doing 60,? as previously mentioned, This model is capable of higher speeds. The exhaust has several functions, some I don't even know about. I do know that the sonic wave helps with scavenging and will return un-burned fuel back into the combustion chamber. With the pipe off, all of that un-burned fuel is just going to waste.



And because of this. When the spark ignites the fuel, the combustion/explosion force will not be as strong. if it had a pipe, the fuel/air mixture would be greater and cause a stronger explosion to force the piston down.

The compression ratio on 78 DT 250 is: 6.7 : 1 - VM28SC carb
The compression ratio on 78 DT 400 is 6.3 : 1. VM34SC carb

So the DT 250 actually has higher compression, but why is the 400 faster? bigger displacement, A big carb also provides more fuel. In summery your pipe would help with power output.

Also: with the pipe you have a spark arrestor and silencer, and it keeps dirt/debris from entering the engine. I know its snowing right now but worst case, snow could enter the exhaust port. Water cannot compress and the engine would hydro-lock.

I am parting out a 1978 DT 250. I can clean the pipe if you are interested. $50 + shipping

Thanks for your answer.
Maybe i sound/look like a noob on this forum but i actually know LOTS about newer engines.
Im a car mechanic.
Ive rebuilt dozens of engines and all my engines runs like new when i rebuild them, if not better than new.
Ive also rebuilt dozens of 2 strokes motorcycle engines.
The only thing stoping me here is the language barrier.
Im a french canadian.
I can speak english as you can tell but i cant express myself as clearly.
When i say that the muffler not installed right now, im not saying the expansion chamber is off the bike, im saying the muffler is off, the expansion chamber is still on, its just the muffler that is off.
Only this part is off right now :


I never run the DT in the snow, i only did it once to make a video for this forum.
I never ran it on dirt either because the suspension doesnt like it. (only did it once and when i did the muffler was still on the bike)
It only runs on pavement usually.
Now the bike is sitting and it will sit till next summer unless i deceide to do an overhaul on it.
Ive never tryed to start a 2 stroke without an expansion chamber, but im gessing it wouldnt even start.

Installing a clean muffler on this DT might improve the performance a bit, but i doubt it since its very restrictive.
Im thinking the problem is somewhere else.
Maybe the crack on the expansion chamber has something to do with it, thats why im going to weld it as soon as possible.
My muffler is in good condition, its only cloged.
When i have some spare time, im going to throw it into my fire pit and unclog it, but i didnt have time to do it yet.

Ive removed the muffler on the RM once to see how it sounded like.
I didnt notice any difference in power, only a huge difference in noise XD
Normally, removing the muffler on a 2 stroke should remove some restriction and lean the mixture, which SHOULD make it more powerfull.
But right now the bike doesnt sound lean so im guessing its still sucking some crankcase oil somewhere (main crankcase gasket perhaps)


To hydro lock the engine with snow is highly unlikely