The 75 is a different setup than the racing manual I sent you. It is for the 72-73. The motors changed significantly for '74, then again for the '75-76 models, then yet again for the '77-79 models. 1977 was the first year for the enduro monoshock bikes, though the MX monoshock models started with the '75-76 models. I am quite familiar with the '75-78 model 400's but not the 250's. I am not of the belief that the top ends are interchangeable between the 250 and 400. I have not seen that conversion done anywhere, though I would not rule it out. The cases mount up the same, and you can bolt a 250 motor into a 400 frame, and vice versa, as the mounting setups are the same. They changed in '77 so those years are not.
The 360 motor ended in '74 as a one year only motor/model. It, like the 400's, was a CDI ignition, while the 250's remained points up until after '77. The ignitions are interchangeable but you need everything. Stator, flywheel and coil of the type (cdi or points) that you are going to. The systems are pretty reliable, but if your pulsar coil goes bad they are quite expensive and very, very hard to find. I have another contact in North Carolina who can restore the stator to better than new if your's needs that. Let me know.
Up until '76, ('75 if it is a Canadian model) the bikes did not have voltage regulators and are prone to blowing bulbs. You need a good battery to act as an electrical sink or add a 6 volt voltage regulator. The latter is in a Yamaha factory service bulletin.
There is a really neat 12 volt/CDI conversion which is available from Germany from Powerdynamo (
http://www.powerdynamo.biz/eng/systems/7238/7238dcmain.htm)which a friend of mine in Idaho helped develop. It works well and is fairly bolt in.
You can bolt an MX motor into an enduro frame, but they lack the oil pump which will mean premix, though it is possible to add one to the MX motor I believe. That is part of my build plan for mine.
Chambers for these bikes are pretty limited as they are a through the frame design. You could build a down pipe or add something. Bassini made a great chamber, but they are kind of spendy and hard to find. I have an interesting NOS through-the-frame chamber which is slated for an MX based street tracker on my to do list.
Here is a link to the correct wiring diagram for your bike year:
s93795793.onlinehome.us/pdf/wiring%20diagrams/dt250b%20wiring%20diagram.pdf[/b]]s93795793.onlinehome.us/pdf/wiring%20diagrams/dt250b%20wiring%20diagram.pdf
I have several paper manuals for the 75-76 models, but none have been scanned to PDF. Let me know if you need anything in particular.
The stock 75 DT250 was rated at 24 hp at 7,000 rpm while the DT400 of the same year put out only 27 hp but at 5,000 rpm. There is a huge seat of the pants torque difference in the 400. There was no MX 250 of those years I can find, but the MX400 motor for 1975 put out 38 hp at 8,000 rpm. That motor would give you the biggest HP increase, but I am sure running a streetable exhaust would cut down HP somewhat.
They are not bad streetable enduros in stock form, having ridden mine about 6-7,000 mile on the TAT trip(s). We did about 2,200 miles of street/gravel/trail/desert loaded heavily with supplies and extra fuel. I maintained an average of about 40 MPG on the road with my 400 and it was not ridden easily.