I have been learning, somewhat the hard way.  I just had 2 cylinders
replaced at 340 hours for leaking exhaust valves.  
What happened?
1.  I run LOP always- 70-80 LOP
2.  I had GAMI injectors installed at about 150 hours.
3.  My timing was at 30 degrees BTDC instead of 24-my error and a bad
error.
4.  My TIT in climb was 1515-1530 which is too hot.  Too lean of fuel at
2500 rpm and 30'5".  Fuel flow was 25.5 gph in climb.
5.  My oil analysis showed the last reading of nickel being slightly
above normal.  (It is my understanding that nickel is only from exhaust
valve guides and valve stems.)

What did I change?
1.  I set the timing to correct.
2.  I increased my fuel flow to 46gph at 100% power-2700 rpm and 38.5"
MP.  I now see 1340 TIT on climb at 2500 rpm and 30.5" which is where it
should be. And fuel flow is 33gph.  I am slightly on the rich side of
fuel flow, so I can now lean on climb just slightly to get the TIT at
1320-1350.
4.  I am leaning very slowly to 120 ROP to bring the head temperatures
back slowly.  I then lean rapidly to 70 LOP.

Before changing the cylinders, I went flying again for 12 more hours
knowing that I had 2 leaky valves but the compressions were not low
enough to ground the plane.  With 12 hours with everything set
correctly, the oil analysis showed that the nickel was normal.  My
conclusion is that I had solved the burning valves by correcting the
timing and increasing the fuel flow.  I still ran 70-80 LOP.

What went wrong?
1.  Timing off is really bad.
2.  Climbing too hot is really bad.
3.  I assumed the factory timing and fuel set up was correct.  Bad
assumption.

Advice:
1.  Check the engine setup- don't assume it is correct from the factory.
2.  If running ROP you need to be at least 120 degrees ROP which is
about 22.5 gph on my 550.
3.  LOP of you need to be 70 LOP.
4.  Go to the GAMI course.  I am going to go and learn what I should
have learned  before learning the hard way.  
5.  Make certain that your mechanic does not make any assumptions and
goes through everything.

TCM's input
1.  Always run ROP.
2.  The timing could not have been that far off from the factory and
slipped on both mags by 6 degrees. (No one else believes that the mags
will both slip that much.)
3.  I was leaning too fast.

GAMI's input (George Braly)
1.  Set up and engine right.  I had too high TIT temps in climb.
2.  With the timing advanced by 6 dgrees I was fortunate I was running
LOP and low power or the engine would have had a catastrophic failure.
3.  Go to his course on engine management.

Inspection of the 2 cylinders and pistons removed:  They looked great,
no grooves, no scuffing, no ring wear.  The cams and lifters all looked
great.  If there were not under warranty I would have had the valves
redone and reinstalled the cylinders.

TCM was great to work with under warranty.

Carl Cadwell
N25CL IVP