There are a couple of things I am confused with, or perhaps mayby I dont understand it that well.
I ALWAYS THOUGHT THAT 25:1 MEANS 25 PARTS FUEL TO 1 PART OIL. You state it will be LEANER than 50:1 ??? How when I have twice the amount of oil to the mix than 50 to 1
Have I got it around the wrong way?
It is easy and very common to confuse the gas-air ratio with the gas-oil ratio.
Lean means more air relative to gas, or a low "gas-air" ratio.
Rich means high "gas - air"ratio.
Oil has nothing directly to do with how rich the gas-air ratios is - that is determined by the gas-air ratio.
However, oil affects the richness indirectly but in an opposite sense.
If your mix has more oil and less gas (eg 25:1) then if the same amount of mix enters the chamber as a 50:1 mix, then the 25:1 mix produces a leaner gas air ratio.
Some of the oil components do not burn but scavenge soot and smoke (ie unburnt oil and gas) this robs the mix of gas and effectively leans the gas-air ratio.
The difference is small but it may be enough to cook a saw if someone switches from a saw tuned for 50:1 to 25:1 without retuning.
The solution of course is to retuned to allow more mix into the saw which richens the air-gas ratio. But on low "gas-oil" ratios this then injects more oil (which for modern saws is totally unnecessary) as all the does is fog the air around the operator with crap. The difference between 25:1 and 50:1 and even 40:1 on modern saws is significant and I find it leaves my chaps, skin and hair all greasy after a days work, plus I get a headache.
I find it ironic that operators put more oil in their mix which pollutes their working environment and then have to invent drive mechanisms to get away from it whereas if they were a bit more careful about how much oil is used they can still operate up close and personal with the saw. The other mod that is useful is a muffler mod which allows the saw to breath easier and if carefully implemented directs the exhaust and saw dust away from the operator.
A constant feed rate is not needed to getting a good finish, and, just like like using log slope alone, an unchanging counterweight system will not produce a constant feed rate anyway. As the saw works its way down the log the chain gets blunter and will slow down, so extra counter weight will be needed to maintain a constant feed rate. Also most logs vary in cutting width so if you start at the fat end the maximum feed rate will be slow, and as the saw gets near the skinnier end the feed rate will increase. When cutting slabs that are not so wide you will need one weight, while cutting wider slabs will need heavier weight to maintain constant feed rate. When I tried a counter weight system I found I was spending too much time putting weights (bricks in a hessian bag) into and out of the bag. I quickly found I could always cut faster by just sloping the log and being up close and adjusting the additional cutting pressure (needed to maintain optimum cutting speed) on the wrap handle with my left knee or thigh. This leaves arms free to drive wedges into the kerf. Unless an operator can find a way to automatically drive wedges in while away from the saw they have to be reasonably close to the saw anyway.
A constant feed rate is possible using a big powerhead cutting relatively soft and narrow wood, and a constant speed drive - either hydraulic or electric. However, when the wood gets big and hard the saw will simply not cut a constant rate. While constant feed rate will produce a good finish it is not essential to producing a good finish. Variable force cutting can produce remarkably smooth cuts provided the force is not varied too quickly. The main thing is to just be gentle eg not to FANG the saw back into the cut when for whatever reason the stop mid cut. The other problems with finish from alaskan type mills; eg not seesawing the saw down the log, should not be a problem for a carriage mill. I reckon a better solution to applying a constant force than a counterweight is a winch because the operator can easily vary that force in a smooth way.
I don't usually mill above 38ºC but there are a lot of people that do without any problems.