How fast was it climbing? Were you ROP?
Rapidly climbing CHTs are often a sign of moderate or greater, detonation. If it went from 350 to 380, while all others stayed at 350, in less than 30 seconds or so, that would be my first guess. Detonation can occur from multiple causes, but a borescope inspection would probably be a good start, looking for carbon chunks that could cause pre-ignition.
Look at the spark plug wires that are in close contact with the #1 plug wires. Sometimes they wear badly and the energy can jump from one wire to another, creating a very advanced ignition event that causes the detonation. This often happens when one plug or wire has a high resistance and the energy finds less resistance jumping wires than it does through the bad plug/wire. Put an ohmmeter on each wire and plug. Not sure that this is possible on a 4 cyl engine though.
If you climb excessively rich and the CHT rise was slower, a mildly clogged injector is also possible. If you were in the neighborhood of 100* ROP during the climb, mixture cannot realistically account for the 30* CHT rise, as 50-100 ROP creates the highest CHTs. However, if you are climbing at 250-300 ROP, then dropping the #1 mixture to 50 ROP, via reduced injector flow, will up the CHTs a decent amount, relative to the others. This makes some sense, as the onset of symptoms was sudden. If this were the case, EGT readings should have confirmed it. Do you have logs you can check?
You can also do another test and let the #1 CHT rise higher, maybe 425. If the #1 CHT rapidly goes all the way to 425 or greater on #1, with the others at 350, it is highly likely that detonation is the cause. A clogged injector cannot realistically cause this level of CHT rise.
Larry
