2.7 CIS engine : Running lean after MSD box install.
 

I just finished installing a MSD ignition box (6425, the new digital one) to my 1976 2.7 CIS engine, everything went smooth and well, I also put a new set of WR5 bosch plugs with .045 gap as recommended. The car started right up and idled smooth until it warmed up then I've noticed the idle dropped from 1000 to about 600-700 and idles a bit rough, the AFR was between 15-17 when idle. the car was running great before the MSD and idled right at 14.5 to 14.7 @ idle (1000 rpm). Is it normal to have a lean mixture after the MSD box? is it because I got a more complete burning of fuel? I don't want to play with my CIS setup because it was really spot on before the MSD box install!

Not sure why the MSD changed things, but usually the cars like to be closer to 13 at idle. I think you may have been pretty lean to start with.

You may need to bump the idle up a bit. I had to when I installed my MSD Street Fire and Blaster Coil. Ran better than before after the ignition install. You might want to use a gas analyzer or install a wide band O2 sensor to fine tune the system to your liking.

-Steve

could be the old one was weak in some area.

if you can check the AFR at 3k steady speed.

if needed, richen it up. it appears you have to the tools to check it.