I posted this link over at ATAG but will put it in here. It's worth a careful read but here is a paragraph that I think is very relevent if u haven't got the mixture orientation correct in CloD
http://flighttraining.aopa.org/stude...l/mixture.html
"Excessive leaning at cruise power above 75-percent power will invite engine damage from overheated valves and incur the possibility of detonation. The probability of damage from over-leaning decreases rapidly as cruise power is reduced from 75 percent. For example, there is considerably less, if even any, possibility of engine damage from over-lean mixtures at 50-percent power. However, an over-lean mixture can foul spark plugs and combustion chambers because of cylinder misfiring.
Many older engines are equipped with non-alloy steel exhaust valves. During normal cruise power (approximately 50 percent to 75 percent) the exhaust valve will become glowing hot during the period that it is open and exposed to the hot gases leaving the cylinder. If the mixture is lean enough to create an oxidizing atmosphere, the exhaust valves usually will be damaged. (An oxidizing atmosphere is always present in lean mixtures.)"
This may be why u are getting rough performance Ivank if your mix levers are all the way back and u are using more than 75% power and/or climbing.