Hi, unless you wish to run your own dedicated server, there's no need to open any ports on the router. During the installation, the game creates 2 inbound rules for ..\ SteamApps\common\Kart Racing Pro\kart.exe in Windows Firewall (Protocol Type: UDP, Local port: All Ports, Remote port: All Ports and Protocol Type: TCP, Local port: All Ports, Remote port: All Ports), nothing else is required.
Try to check with your new ISP if you can get a dedicated public IP address (sometimes it comes as a part of the package, sometimes they charge you a bit extra for it). I use a dedicated public IP provided by my ISP, no KRP-specific ports open on the router, there're default Windows firewall settings for the game on my PC and no issues connecting to public servers, unless they are password-protected or use the content which I don't have.
Also, if using wifi to connect your PC to the router, make sure the connection is nice and stable, poor wifi speed can cause timeout errors.
Try to check with your new ISP if you can get a dedicated public IP address (sometimes it comes as a part of the package, sometimes they charge you a bit extra for it). I use a dedicated public IP provided by my ISP, no KRP-specific ports open on the router, there're default Windows firewall settings for the game on my PC and no issues connecting to public servers, unless they are password-protected or use the content which I don't have.
Also, if using wifi to connect your PC to the router, make sure the connection is nice and stable, poor wifi speed can cause timeout errors.