Thanks everybody for the answers!
I builded this TH400 one more time, specs:
Direct clutch - the same cluth pack (7 frictions, 7 steels, Red Eagle), drilled a hole 1,5mm, installed return springs.
This is photos after 3 starts with trasnbreak, max engine power.
Direct clutch pack:
Looks burned near backing plate. Slow releasing after transbreak? Need more diameter hole?
Direct clutch return springs, one installed for example. Used all springs when building.
Direct drum. Check valve and bleed hole opposite to it.
Forward clutch pack. As new. Forward drum has 1,3mm bleed hole and all return springs, but they are shorter and less harder then direct drum return springs.
Intermediate clutch pack. Burned near piston. Why?
IC burned friction.
Center support orifice for IC apply piston.
Center support return springs (3).