Help me identify this yamaha

[kaneys]

My name is mark and I live in australia.. I have a Yamaha motorcross bike that has belonged to my wife for about 10years. We dont really know what it is.
At first glance it looks like a DT400 engine in a MX250B frame, but the guys at Yamaha had it for a couple of weeks and said there have been Modifications
Frame # 509-007392
Engine # 574-000323
there is a 50000 stamped under the head fins

From what I can see the 574- engine number is not a dt400 number at all

Any assisttance you can give us would be greatly appreciated

 

[High Lord Gomer]

Sorry, no help based on the numbers. Can you post a pic? If it won't let you, email it to me and I'll get it added so some of the old geezers here can help.

highlordgomer at themxtrack dot com

 

[kaneys]

Some pics

 

[Bonehead]

thats MX250 1975 or 76 I tride to post a pic but it is already posted in a post called barn find in the vintage section. Could be a 79 thats the year they put YAMAHA on the seat like that

 

[dirt bike dave]

Yep, the 509- frame # is for a 1975 MX250B according to this page

http://www.merrittmotorcyclesalvage.com/yamahaidentification.htm

 

[dirt bike dave]

Here is the link to Bonehead's thread http://www.dirtrider.net/forums3/showthread.php?t=182511&highlight=barn

That thread has a link to another thread about an MX250B.

 

[Bonehead]

I will take that Old Geezer as a complement

 

[rob the snail]

cant be 79, swingarm is steel in the pic