Cam overlap...
 

Is there any way to reduce unburned fuel waste at idle, for instance, other than dialing down your fuel pressure on your FPR to just before lean?
I am cam illiterate, and am tired of running rich. I have been told that there is NO way to get around it because the cam I am running (B-303, Crane 2041, same thing) has overlap.
I have a feeling this is just something you have to live with...although I am not really complaining.
I will shut up now...

MM&FF December 2002 issue

Cam overlap article, I can get the page # for you tonight.

It might help a little. I'm sure you could get a custom grind to closer do what you are refering to. Keep in mind though, running rich is caused by more than just the cam overlap. Bad 02 sensors are common for this.