this isn't a saw that's been sitting around for 10-15 years with old gas in it.
I hope no one here gets pissed at me or thinks I'm a "grumpy old man". I just want to make my point more clear since I have posted several times on this topic.
OK, read back to the first post. Saw has seen ethanol. I have seen ethanol damage in carburetors, mainly from the moisture it attracts which ends up in the form of "white rust" or oxidation. The low circuit ports under the welsh plug are not easily cleaned by carb cleaner because the cleaner may not even reach the "clogged" port or ports. He can try but I wouldn't be afraid to bet that he will be removing the carburetor....again.
In my experience I have found that there are three sure fire methods of cleaning the hard to get at circuits or ports on these small carburetors today.
First is to employ a ultra sonic cleaner with a chemical called "Mechanic In A Bottle" or "Star-Tron" heated to 110 degrees F for 25-30 minutes. This method in my shop and my former employment has a 98% success rate!
If no ultra sonic cleaner is available, this method can be tried. Empty the fuel tank of all fuel. Pull the starter cord about 10 times to get the fuel that is in the fuel line and the carburetor out and into the cylinder. Now fill the fuel tank with "Mechanic In A Bottle" to a level that is above the fuel pick up / filter. Pull the starter cord at least 15 -20 times so that the chemical is pulled into the carburetor. Let saw sit over night. Next day, empty the fuel tank and add fresh fuel. Saw should start.
If the MIB chemical is not at hand....Third. Remove the welsh plug, clean with carburetor cleaner and compressed air. Install new welsh plug.
If the owner of the saw showed no mechanical ability in his posts, I would have not directed him to pursuing the task of removing the welsh plug. In fact, I first suggested that he just buy a diaphragm and gasket kit but since he bought the complete kit....go for it!.
He came here looking for help. That said, if someone had discouraged or scared me in that respect 40 years ago, I probably would have had to make my living by doing something else. In other words, he needs to get his feet wet sometime or pay the Stihl doctor every time a small problem arises. Its not rocket science! If all else fails, he buys another carburetor. If that is the case, since Stihl bought out Zama, there is a "cheap" Zama carburetor available now for the 026 / MS 260 Pro. I need to look up the part number. Since I retired, that information is no longer at my finger tips. I installed a Zama on a 026 PRO some time ago and I think it cost me around $30 with shipping from eBay. That said, I must also mention that I had to re-leave some of the plastic inside the tank housing with a Dremel tool.

Dave