boot from two hdd

I have two disks (WD hdd and Kingston SSD) in PC. HDD is with Win7 and SSD is with Win 8.1 (both Legacy, No UEFI) and I can boot each OS using BIOS boot menu. More suitable is if I use EasyBCD and I installed version 2.2 to Win 7 and Win 8.1. On Win 8.1 I can get EasyBCD menu with two OS and both are success. Unfortunately EasyBCD in Win 7 can boot Win 7 only (can not recognize Win 8.1 boot).
Why ?
What to do ?