vacuum advance idle issue?

Back to flogging a dead horse, found my leak, carb gasket had halfway disintegrated. Probablu been leaking a long time, bozo thoroughly futsed the timing and idle mixture so as to "work" with a massive leak and no advance. Scares me ito drove it homeround that way. Everything is being set right. BTW will a huge crack in the exaust manifold cause any real harm other than sounding lame?