I have a 18hp Kohler on my exmark lazer z hp. IT started idling funny the other day, and I had to leave the choke on for it to stay running. I cleaned the the air filter and the carb, but it still doesn't run right. It idles rough now but I don't have to use the choke. My local dealer thought that I might have junk in the gas so I tried fresh gas but that did nothing. It feels like I'm not getting enough fuel, but I'm not sure. Also, when I go up hill it loses all power. If any one could help me it would be greatly appreciate.