If anybody own a DT250E id be interested to know the top speed of their bike.
You have to hold my bike full throttle for quite a while to reach 60 mph.
And when you reach it you are at top rpm.
I dont like to go that fast because i dont like to hold a 2 stroke at full throttle because it might blow up.
At first i was thinking that maybe it didnt have the original sprockets, but since it car barely pull the gears its already got, i cant give it any more gears.

On page 7 of this thread you can see my video with the DT250.
At about 4:30 you can see that im in 5th gear and i give it some throttle.
You can see the speedo climbing as the RPM almost reach the top rev.
You can see that at top RPM it will go about 60 mph.

according to this website : www.bikez.com/motorcycles/yamaha_dt_250_mx_1978.php

The top speed is supposed to be around 68 mp/h

I believe that if i give my bike absolute Hell it might reach this speed, but it wouldnt like it.
So i guess its normal.

I have to say that the bike is not fast but it is strong.
I took my girlfriend for a ride one day and it didnt make any difference in the performance with the additional weight.

If someone changed out the front sprocket 1 tooth less than stock it would explain why it only goes 60mph.

According to the website Makotosun provided me, there are 2 OEM size sprockets , a 14 and a 16. Im gonna look on the bike to see what ive got.

On the parts listings for your bike, I believe they show both the 250 and 400 parts on the same list (many parts are the same).

If I'm reading the manual correctly, the 250 came stock with a 14 tooth front and 47 tooth rear sprocket.

Thanks, im working right now so im gonna take a look at that tomorow.
Now that you say that, im wondering if the 400 cylinder would work on the 250 bottom end ?

Nope. Won't fit.

As to top speed, on my 1971 DT-1E, when I rode it in Grand Prix (like the Elsinore GP), I used a 15 tooth countershaft sprocket, and a 44 tooth rear, and pulled 80+ on the long paved straight. Same thing when we pre-rode for the Baja 500 that year (we won the 250 class with a bike I built for San Diego Yamaha won the 250cc class, with riders Armand Caprio and John Kenyon that started as a 250 Enduro).

With stock gearing, I routinely cruised at 75mph on the freeway--and got ticketed for 70 on a 'sidewalk' as well (Long story...)

Hammer

Thanks for your informations, this gives me hope.
Please excuse my obvious lack of knowledge over these enduro bikes, but what is a DT-1E, is it an early version of the DT250, has it got a 250 cc 2 stroke. I guess it has since you raced it in the 250 class, but i want to make sure.

If it is, it surprises me because my bike doesnt feel like it would be able to pull any more gears.When you hammer down the throttle in 4th gear on pavement and you shift to 5th gear, you have to give it FULL throttle to be able to accelerate in 5th. And you feel that it needs all its power to accelerate, and it doesnt accelerate quickly. So i feel that if i give it more gears it simply wont be able to accelerate.
For exemple in 5th gear with my rm , i just touch the throttle and it takes off.
I understand that my Rm is way more powerfull and that i cant compare the 2, but i assume that the Enduro should have some kind of power in 5th gear when it really dont.

I guess that my engine is down on power. That might explain the spark plug problem.
I had a 1994 Rm 250 a few years ago and it blew the spark plugs as well. It was caused by a worn out engine.
When i rebuilt the engine, the problem was solved.

I shall first run a compression test to know whats going on. I suspect that my expansion chamber has something to do with the problem as well.
How many psi should i get from this engine on a dry/cold pressure test ?
I shall also run a leak down test because im pretty sure ive got a problem somewhere.
Maybe i should just open it up and rebuild it.