Oh Lawdy I looked it up and that thing has a flat back on it .

That being the case most likely the diaphragm is puckered where it won't flex enough to get enough fuel in it and runs out lean .
You could try soaking the diaphragm in brake fluid a couple days to soften it up .You might also set the fuel lever a tad high which might help it or it might flood it out .
I don't know if that guy from Sugar Creek supply has the flat back kiits or not .At any rate your'e just going to have to fiddle with it if you don't find a kit . I have a 250 with a flat back I must have had apart a half dozen times before I got it right . This BTW is my least favorite chainsaw carb .