I am having problems with a Stihl 036 Pro. This saw is about 2 years old and has maybe 20 tanks of fuel through it. While cutting wood last week is suddenly would not start without having the choke on all the way. Once it fires I must get on the gas and feather it to get the RPM's up and keep them up to keep it running. If I let it idle it will cough, sputter then die. To restart it the choke must be turned on, pull the starter once and it will fire and die, open the choke, pull and it I can get it going by working the gas. This is what I have done: adjust and readjust the high and low needles to both side of what I consider the normal operating range for my location. Removed the carb and cleaned out the fuel pump and fuel strainer. It did have some sawdust in it. Initially I expected this to solve the problem but it did not. The fuel tank breather is clean. Air filter is clean. Spark plug looks good. I have removed the inlet needle from the bottom of the carb and cleaned that. It was a little dark but not what I consider dirty or worn. There was no annular groove on the end of the needle indicating wear. Removed the high, low, and idle screws and cleaned. Generally cleaned the carb. After reassembling everything the same problem described above continued. I pulled the carb off of a DIFFERENT 036 that is about 8 years old and installed that on the new Pro I am having trouble with. The troublesome Pro saw with the older carb ran flawlessley. This lead me to conclude that the problem is definately in the carb. I do not know what to do/check next. Any advice is greatly appreciated. Thank you, Ryan.