POST 2;
Loose pins on tubular track.
OK, I know I'm in the minority on my use of track but for us traditional (also cheap) track users, some needle nose pliers works great to close up those enlarged holes.
Also, a small hammer works great when the two tracks are pushed together and one rail sticks out farther than the rest.
Also, I find pins are easier to remove, if they are, first, lightly tapped into the rail before removing them with some pliers.
This also eliminated my engines slowing down on the far side of the loop.