Maybe 1-3 are getting dirty.

wrote in message
oups.com...
I've had trouble getting my IO360 to run lean lately - Cylinder 4 EGT
runs a coolest when rich, but when I lean, #4 peaks a LOT later than
the other 3, and at much higher EGT (1500+ compared with 1400+ on the
others. I'm just wondering whether the orifice on #4 could be worn and
now just running too rich generally?