We need more information.
Are you talking about the SAME cigar, some burn fine, but others from the same lot burn “too slow”.
What kind of cigars….brand, size, vitola.
What do you mean they burn too slow and they become “ruined”?
Is the draw the same as the ones that burn properly?
A well packed, dense, 54 ring cigar with a thick broadleaf wrapper and heavy Nicaurguan binder and filler will burn MUCH slower than a lightly filled, 44 ring Connie.
Lots of variables.