Hi, I have found this group as I’m searching the internet for a to possibly purchase a Dt400B. I owned a 250B in the early 80,s as a kid, and restored a 250D in the mid 90’s. Anything I should be aware of with respect to difficult to find parts or quirks of the 400B, to consider when viewing. I’ve got my eye on a bike that looks reasonably complete and fires up but needs recommissioning. It’s a USA import to the uk. I don’t want to chuck loads of money at it restoring it, but would like to achieve a rideable reliable clean bike.
All comments welcome, thanks.

 from near Salisbury, Wiltshire.

CDI pulsers weren't the best. 12v conversions are available, as long as purchase price allows for this cost.

Also allow for replacement of all consumables (chain, sprockets, brake shoes, tyres, possibly cables) if you are the first UK owner.

If CDI is bad, a points magneto from a 74-78 250 is another option.  

Yes. Definitely what Mark T says. I went through a couple of the CDI units (exactly the same units) on a '74 DT360A. Fortunately I had scooped up a magneto assembly from a '75 DT250B. DEET rebuilt that for me, and it has been flawless since.