Low compression motors might run OK at higher speeds, but they won’t idle very well. At higher speeds the compression doesn’t have as much time to leak off, but you still lose some performance.. If your motor sat for a long period and the pistons were gunked up, you may regain some compression after running it a while. Sometimes the piston rings will stick and running them helps them loosen up a bit. I use some Sea Foam in the gas to help in the process. On the other hand, sometimes they are just worn out.
