You mean like this.You have to do this. First question for Stihl guys is, does this saw have impulse line from crank case or pull through carb mounting block? Made my own adapters for pulling vacuum through spark plug hole. Ream out an old spark plug and epoxy rubber line into spark plug base. Easy to check if it's sealed, just hold thumb or plug end and try drawing vacuum. Then block off intake and exhaust with gaskets and homemade plates, make sure decompression valve is closed or plugged. If impulse line come from crank case and is separate, block off intake and exhaust as above and pull 7 lbs of vacuum through line. With those once every now and then saws, you can clean cylinder intake and exhaust then seal with duct tape, it works, but may have to use spare hand to add pressure to tape. This stuff is really not that hard. Hope it goes well.
https://www.arboristsite.com/commun...plug-pressure-vacuum-testing-adapters.282737/Here's another on the principles behind it all and it shows a block off with a piece of rubber to seal the muffler side.
http://www.madsens1.com/saw_airleak.htm