An I4 has primary balance but lacks secondary balance, which is the reason many performance I4 engines like the Mitsu 4G63 have balance shafts.
Some enthusiasts eliminate the balance shafts, install poly engine mounts, then wonder why their econosport feels like it is going to shake apart. Going further, toss in set of 272 cams in a 4G63, and you can get a near V8 feel and sound at idle.