Thanks for all the Info StihlHead........
Not a problem. After I dumped all my 025 size saws and replaced them with 026/260s, I got to playing with them. There are a ton of differences in year models, and they are fun and easy to work on and modify. They are easy to fully port as well. Porting has several stages. The first stage is opening up the muffler and richening up the carb.
WARNING! do not modify an 026/260 with a fixed H jet! You will score the motor in no time running it too lean!! Also if you have a newer 260 with a limiter tab on an adjustable H jet carb, you will need to pull the limiter and trim that tab so that the H jet can be richened up, or you will score the motor in no time running it too lean
OK, warning over... oops, I forgot one more thing:
WARNING! The EPA has mandated that any chainsaw that has been modified that is then worked on by a dealer, that dealer is required by law to restore the chainsaw to its original condition. Meaning that they will replace the carb limiter and/or muffler with OEM original parts if you take a modified saw in for repair...
OK, other warning over... where was I? Oh yes, the joy of porting a 260 saw. The first stage I have shown here in photos, open up the muffler. You can do that by drilling one out, or replacing it with an earlier model muffler. The 026 IPL has the three mufflers shown with part numbers. Once they are opened up, re-tune the carb so that it burples or 4-strokes at WOT, and runs smooth in the wood. Even with just that mod, the saw will run a lot cooler and a lot stronger. Upward of 10% improvement. This muffler porting keeps the saw more or less in the noise range as it was when it was stock. More muffler holes means a lot more noise, but they will run even better.
The next more serious stage of porting is called a woods port, or a light porting for a saw that is intended to be used a lot. I recommend that you have a digital tachometer for tuning your saw to do this. For this you mod the muffler as above and then use a grinder (like a Dremel tool) and open up the exhaust port on the right and left side to widen it (and square it out more). Also open up the intake port to widen that, and polish the exhaust port (but not the intake, a rough intake port is better). Do not raise or lower the port openings unless you know something about port timing. That will allow more air and fuel mix into and out of the engine, and it will run stonger as a result. Along with that you can use a piece of fine emery paper on a thick piece of glass, and use that to file down the base of the cylinder to as much as the thickness of the base gasket. That will increase the compression and add more power to the saw. You have to be careful not to shave off too much of the cylinder base though, or the piston will hit the top of the cylinder at TDC. Some people just remove the cylinder base gasket to get the same effect, but I prefer to keep the gasket for a better seal. You also want to leave enough of what is called the 'squish' at TDC. I have done several of these types of port jobs with muffler mods on 026s, and they absolutely scream. I have raised the max RPM up to 15k after these mods. While that may seem high, all the Stihl max RPM limits are set 500 RPM below the actual red line for safety reasons. The actual 026 red line is at 14,500, so it is only 500 over stock. It is running rich enough, and I have not had it overheat on me. To see if the saw is running lean run it hot WOT in wood for 30 seconds, and kill it. Then pull the plug after it cools and have a look. It should be tan. If it is white, it is running too lean. Richen it up.
The more radical porting stages are typically done for racing and limited use. They are best left to known saw modifiers as they take special tools and a lot of experience. I have seen some fully modified saws that were wreaks, and they barely had the power of a stock saw. For this reason many ported saws do not command a premium over stock saws, even though they may have hundreds more dollars put into them. These mods typically involve opening up the exhaust port even more and raising/lowering the ports it to get more gasses out of there faster. You can also widen and/or polish up the piston and cylinder transfer ports, as well as lighten up the piston to reduce the weight. You can also change out the H jet in the carb to get more gas in there. The stock 026 carbs are rather small, and radical porting is limited by the amount of gasoline that you can get in there. Some guys have put in 044 carbs to get around this limitation. They also drill more holes in the mufflers (though they become seriously LOUDER!). They also lighten up bars and use special chains for speed cutting. Usually they are square ground full chisel chains, and they are rather fragile. You can also mess with expansion chambers on saws, but that gets into hot saws and is beyond my experience of saw modifications. In the end? The 026/260 can be modified a little or a lot, and they will scream a little or a lot more. There is nothing more amusing than handing someone a modified 50cc saw that thinks it will run like an old tired 50cc saw (which it looks like), and WHAM! It rips through the wood like a new 60cc saw, and they think, WTF? I sold two woods ported 026s that way. They had to have them!
) 
