First post so here goes. After cutting grass for maybe an hour, I go to idle and let it sit for maybe a minute and then shut down. Maybe 1 out of 3 or 4 times it will backfire. I had the dealer try to fix this after 5 hrs. on the hobbs and it still does it. I would think that letting it cool down would help this but I guess not. Also I am using synthetic oil since the 25 hr change. Is this ok?