Cheers YAMAYEEHA,useful information that,but i am curious as to how you know that my tank.is a DT2 mx tank and not an 360mx tank.What are the differences.

The way I read it is he said you DON'T have a DT2MX tank or it would fit?

Yes the MX's are different than the RT's. Mainly I think of the pipe on the MX pass through the frame. That changes things.
See the pics of an i think a RTMX vs a MX360. 
 
 

Opps, that Slash X bike is a DT2-MX I think.

I have a Yamaha tank, white letters on silver, black stripe if anybody is interested.

My tank is definately form the bike in the second picture,not the, Slash X Bike..The tank has no petrol tap,could i fit an aftermarket one.L dont want to seize it ,if theres not enough flow from it.

I have an MX360 tank and I had to find a OEM fuel valve. They are pretty easy to find on eBay. I forgot how much but it was not too bad I recall. The threads on the tank for the valve are very fine and yes you will mess them up very easily if you don't have exactly the right threads on the valve. I Googled and found this.

www.amazon.com/Valve-Petcock-1973-1981-Y..._=fplfs&psc=1&smid=A

Hope this helps.

Niche cycles has some petcocks with Yamaha part numbers listed. I ordered one and was able to swap the nut to fit a 71 Suzuki tc50. The nut that attaches to tank will come off and if your threads on petcock are same you can swap the new unit on the old nut. I don’t remember if it was the gt 80 or 74 mx 175 petcock.

www.nichecycle.com/ncs/catalogsearch/res...=price&p=2&q=Petcock