I have all echo equipment and have always been told by the dealer to use echo oil. Well my problem is that it seems that every month and a half I got to take the muffler off my echo 265T and clean the exhaust port. Is this normal? I used 93 octane thinking that this would help the problem from the last cleaning, now I will go back to midgrade gas and use a different oil. I got to get a better oil that does not do this. Any suggestions of oils?