First please be patient as I am not a mechanic. I have had 2 dolmar ps540 saws go bad. I am very careful in mixing the fuel mixture and only used dolmar fuel mix. When the first one stopped running I knew I mixed the fuel correctly as I put exactly the right amount of fuel in the gas can and correct fuel mixture. My friend who used to sell Dolmar saws removed the muffler and I had a scored cylindar wall. He stated it was obvious debris passed through the carburator. I naturally did something wrong. I bought another 540 and it lasted only 18 months. I was careful in mixing fuel and cleaned air filter regularly. Is there a problem with saws and the use of ethanol since reg gas cannot be purchased in the USA? Is there a way to buy affordable piston etc and modify saw to avoid this problem in the future?