I would highly suggest moving the clip on the carburetor's needle down a notch or two. It is running lean without a doubt. Those rpms shot up and stayed there for a while, and a properly tuned 2t motor will drop rpms faster and have a snappy/crackling idle with a very pronounced combustion that makes a "ting ting ting tating ting" sound. Right now, it's a mumble wine because it's lean. Sometimes the restrictive exhaust gets rid of the popping sound but there's no visible oil and those rpms stayed higher than where they should be.
https://www.youtube.com/watch?v=JbQny3DUTIc Look at how this kx does not pop, it has a very soft hitting sound/wine. It also revs to the moon and stays there. No visible oil coming out the exhaust either. That will eventually be a blown up bike, seized at best. Here's what a proper mixture sounds and looks like -
https://www.youtube.com/watch?v=pHkVYM42KsA hear how it makes a popping noise and emits a little oil? I had a kx100 and it made the same poping sound when properly tuned, the engine displacement is not a factor here as any lean 2t engine will sound vastly different from a rich 2t. If you are running a rich oil mix and still don't see oil out of your exhaust, the air/fuel mix is very lean. I'd get the mixture right before doing anything else as adding a pipe might make the problem worse and you'll wonder why the pipe made it do (xyz) when it was really the lean air/fuel ratio screwing things up.