I know, Briz. What I am showing Patrick how to do is to cool it down a little without hurting performance. Most of my experience is with the center cylinders on Jap triples, the inner cylinders on Jap fours, and the hotter running cylinders on other motors. My figuring is the principles are the same.
Tonight I will look in my used plugs box and see if I can take a picture of the ring I am talking about. It tells about the spark advance, at least on gasoline powered engines. The rings should be the same distances down the center electrodes on both plugs if the spark leads are the same for both jugs. A ring that is further down one electrode than the other indicates the timing is advanced in that cylinder. That is something to check for and it is not uncommon.
The next thing to check is to put the pistons and cylinders back on and to check the deck heights on each cylinder at TDC. A piston that projects up further than the other can cause problems. This is also a good time to measure the bores and how far the pistons are from the decks at BDC. The eroded head is reconstructed with modeling clay and all four heads are cc'ed, the head gaskets are measured and the static compression ratio is calculated for both cylinders with the old and new heads. The measured compression ratio should not be higher for the back cylinder.
The measured ratios can be a real "eye opener" a lot of the time.
The last thing is to verify there are no air leaks in the plumbing, or constrictions, to the hot jug or other things that cause it to run leaner than the cooler one. This does not apply here, but it is good to remember on two carb bikes with one carb in the back is the rear one can be sucking hotter air than the front one. It is not unusual to have slightly different jetting on the front and rear carbs.
At this stage any problems are corrected, and if needed, and I richen the mixture to the hot cyl and lower its compression until it cools down. This is what I do, it seems to work, and I am no fancy engine tuner. Tell me if I am wrong on anything or if there is a better way.
x2! Your procedure is right on the money!
The generalized tried & true dyno tuner's methodology for repairing/band aiding a hot/weak cylinder:
1/ Determine which cylinder(s) is(are) the problem.
a/ via s/plug check
b/ via EGT
c/ via fuel flow differences
d/ via air flow differences
e/ via ignition timing check,
per each cylinder f/ via localized coolant temperature check (mostly for water cooled engines)
g/ etc, via data logging/other data accumulation
h/ C/ratio double check for differences in: chamber cc's, piston deck heights, valve relief depth, crevice volume, etc.
2/ Equalize or repair any discrepancies found,
if possible . . . . . .3/ Compensate for any discrepancies in the weak/hot cylinder that can not be equalized or repaired.
a/ richen fuel
b/ retard ignition timing
c/ lower coolant temperature (this can be trickey/impossible with air/oil cooled engines . . . .)
d/ increase coolant volume (again, this can be trickey/impossible with air/oil cooled engines . . . .)
e/ lower air/fuel temperature
f/ lower compression ratio of weak/hot hole (obviously, this is a last resort)
4/ Confirm your corrective action
a/ via s/plug check
b/ via dyno run data
c/ via EGT
d/ via other data accumulation
e/ etc.
Yeah, I know it's a long and complicated list and process. But it sure beats coating the inside of your exhaust system with aluminum, or driving over a con-rod/piston . . .
It's why they call it development engineering . . . . . .
Everyone and anyone feel free to add to this list or chime in on your experience/solution(s).
Fordboy