[Limited]

try tightening up the y pipe on the exhaust manifold,and tightening the bolts on the intake manifold. check the resistance of your leads, check for arcing on the leads, checked your spark plugs?gives you a good indication of mixtures.if they're dark / wet, its running rich, but I don't think the mixtures are adjustable.
does it struggle to rev? it may be worth pullin the pipe off the back of the cat and making sure the monolith inside has'nt collapsed.