What I know about milling can be written on a postage stamp with a permanent marker - but I do know that letting up on the throttle at the end of a cut saves a massive over rev when the saw comes out of the wood. Makes sense to me to operate a saw with some sense of sympathy to the machine. Even a limited coil can only do so much, if the load drops suddenly the revs will spike much higher than in any other situation. Forces rise exponentially with revs, I forget the exact numbers, but 15000rpm is probably 4 times the force on all engine components of 14000rpm.
As to jetting - transfer circuits have to be MUCH richer than wfo or idle. That sudden burst of air when the throttle is cracked needs a big lump of fuel to compensate or an engine will stumble instead of spooling up. Doesn't matter carby, EFI, whatever - this is an important tuning point. On a programmable efi setup you can tune how long that "extra" fuel is in the program after a throttle blip. A chainsaw carb doesn't know the difference between constant 3/4 throttle and 3/4 throttle for an instant as you spool up the saw.
As this part of the throttle response on a saw is effected by both low and high speed needles I'm certain a safe fuel tune can be found for extended part throttle running. It wouldn't take a genius - but perhaps an extra hand - to tune a saw while milling at 3/4 throttle so as it four strokes when you lift pressure in the cut but cleans up under load.
What I'm not certain about is ignition timing tuning for extended running at less than full revs. The ignition timing has no input for throttle position (don't know about at/mtronic), so I can imagine a situation where it is possible that ignition timing is too advanced for safe long term running at part throttle/reduced revs in a situation where load is suddenly increased (hitting a knot, etc), or decreased (reducing pressure in the cut). Best guess is it should be fine as ignition timing usually needs to be lower in a transition stage than constant revs, and a saw transfers through those rev points a gazillion times a day limbing and bucking.
Couple things:
The forces resulting from momentary accelerataions of engine bits are proportional to the square (second power) of engine speed. Not at all exponential. For small increments, that's twice.
(X + a)^2 + X^2 + 2*X*a + a^2 If a << X, that can be simplified by dropping the a^2.
(IOW, for a 2% engine speed increase, peak forces would go up 4%. For your example, of 14K to 15K, a 7% increase of speed, you see approx 14% peak force increment.
The metering circuits of diaphragm carbs are extremely basic, nothing like Weber or SU carbs. Only the idle circuit involves air/fuel emulsions for idle and off-idle. That certainly helps to vaporize fuel and help it burn, moderating the need for extreme richness here. The main mixture just keeps going richer as speed and throttle opening increases until 4-stroking identifies excessive richness.
Reducing throttle when an engine is tending to over-rev may well have the effect of leaning the mixture toward optimum, while lowering combustion temps, not to mention reducing multiple (inertial and power transmission) mechanical stresses. Some experts explain another mechanical threat of extended extreme engine speed, like holding throttle WO for extended limbing, increasing likelihood of detonation unless octane is increased. This seems to go in the face of the 4-stroking, excessive richness, we'd expect to kick in there. Besides, running an engine that way, beyond the power peak, is simply abusive.
Lots of variables to deal with here, making for no single simple solution. Helps to have a range of saw sizes for the job, to simplify some.
That was the first and only time I have ever milled and didn't want to over heat my pride and joy, lol. I'm just not used to extended cut times. I was admittedly being overly cautious.
