I've found this to be a problem with multiple Evolution engines recently. My early EVO 46 engines ran great with no problems (5+ years old). I recently purchased (last 2-3 years) 52 and 61 engines. Both will not shut off when the carb barrel is fully closed. I've given up on EVO engines for this reason. Just replaced the 61 with an O.S. 65AX and will be replacing the 52 with an O.S. 46AX as soon as the 65 is broken-in and flying. I'd rather be flying than troubleshooting air leaks. Overall, I've found that my planes with O.S. engines run more reliably.