Bought a 2009 Gravely 260 a few weeks ago, which now has slightly over 50 hours. My wife ran it most of the time when we first got it, and she said it backfired on her a couple of times when it was new. It has the 27 horse, air cooled Kawi. All was fine until Sunday, when I noticed that when running at slower speeds, with the blades disengaged, the motor began to surge, and stumble a bit, occasionally popping, or backfiring slightly. Increasing throttle, with no load only makes it worse. At full throttle, under load (blade engaged), it runs smooth with full power, but disengage the blades, and it will begin surging, backfiring and stumbling again. Choking almost 3/4 seems to make it run slightly smoother, but still not right. Dealer mechanic said he thinks it is in the carb, and has ordered new parts for a carb rebuild, but I'm not totally convinced that is the whole problem, but am not much of a mechanic, so thought I'd ask you guys that are. I always thought backfiring was a sign of a problem with the timing, but I may be wrong. Just thought I'd get some input in case the carb parts don't do the trick, or possibly can suggest something else for the mechanic to check. Thanks.