wrong uplink causing public ip couldn't be ping

hi, i have 2 uplink on my network. one is on private ip (192.168.1.1) another is on public ip (202.xx.xx.xx). i point my router default gateway to the private ip. i found that my public ip coudln’t be ping from internet, although i could ping and browse using the public ip connection. but if i point my def.gateway to public ip, my public ip could be ping from internet. can anyone help me with this so my router public ip could be access from internet?. thank you.