I replaced the crank bearings in my DT400. I have the Tusk crank puller, but it doesn't work on the right side. What can I use? 

Warm the case to about 120*C and the crank will drop straight in.   

If the bearing is in the case, , & you're just wanting to slide the crank in, the crank is a slide fit in 'that' bearing not tight like the left one. All held over by the crank nut & gear. Bearing is tight in the case of course.

Bearings yes . Freeze them
120 degrees hot on the cases and the freezer bearing will slide right in. But..may need a slight push to seat it down.
Listen for the tell tale.. clunk .
 

OOPSY. well Duh..... look at the picture Rick, ( sometimes I don't scroll up OK !!! )
My bad.
Got a DEET Crankshaft puller for pulling and setting all crank stuff  ?
Works wonders

I think this side has two 8mm threaded holes that can accept a 2 bolt puller if I recall

lesson I learned is that 225F seems to be the magic temp for bearings to drop into case for what its worth

No issues getting the bearing to drop in. I put the crank in a zip lok bag and put it in the freezer for 2 days. The crank will go in the bearing leaving about a 1/4" gap from seating all the way. I will heat the case up and get the crank from the freezer and see if that does the trick. I can't remember how we did it back in the 70's.

Heated the case and the frozen crank dropped right in. Thanks guys!