i have a 1975 dt 250 motor stuck in a 1978 yz frame & was wanting to do away with the points ignition & put in a pointless cdi unit anybody have any info on what cdi unit out of another yamaha i could use don't want the internal rotor want to stay with the external rotor since this is going to be just a play bike & don't care about a lighting circuit either

A later DT with cdi would be a good place to start. You'd get decent lights as well. You can buy kits, with new generators but these are normally upwards of £400.

If using another yamaha one you will need both the stator and the rotor from the CDi generator. Between the 2 they set the ignition timing and using mis-matched ones simply doesn't work. You must also know what year the generator is from as Yamaha had a nasty habit of making minor changes to the generators that would render them unswapable with ones from other years, not in terms of fitting to the engine, but the electrics inside. The cdi box must be matched to the generator as well for the same reason.

i have a 1975 dt 250 motor stuck in a 1978 yz frame & was wanting to do away with the points ignition & put in a pointless cdi unit anybody have any info on what cdi unit out of another yamaha i could use don't want the internal rotor want to stay with the external rotor since this is going to be just a play bike & don't care about a lighting circuit either

TBH for a field bike you may as well stay as you are, you would need the flywheel, stator plate, coils, pick up, sub loom and cdi unit. All this needs to come from a 78 on dt 250/400. I don't know if the flywheels are interchangable either. They are on the 175 if you swap out points for cdi but i don't know on the 250.

Neither of these bikes (DT250 or DT400) are all that common and price wise i think you would be looking at £50 plus for the generator assy, stick a chunk more on for the cdi, plus wiring and you have a bike no faster than the one you have that you can't fix in the field, so to speak.

^+1 Thats what i was thinking too, not worth the searching, the work to fit and the expense for a field bike, points will be just as good here.