I've got a 25hp Kaw. with 1400 hours on a Wright Stander and 2 weeks ago it started acting up. I'm pretty new to mechanics of small engines and I don't know what might be wrong. What's happening is the engine sputters. When the rpm's are raised from idle it sputters worse and then gets better slightly. When the engine is put under load, either a rapid acceleration to top speed from a dead stop or the engagement of the blades, the engine really sputters and bogs down. This problem is not there 100% of the time. Many times the mower will work perfectly. Other times it will be fine and then after a few minutes of operation it will start to sputter. Still other times it will just be sputtering right from start up. I've already replaced the fuel filter, checked the spark plugs and they are fine. This problem started after I checked the valve clearance but I rechecked them and they are tight and at spec. I also had a negative battery cable break at the same time as the valve check but it, too, was replaced. I'm also noticing a tiny bit of blue-ish smoke from time to time on either start up from cold or when the rpm's are raised. There isn't very much that comes out the exhaust, nor am I noticing my oil level dropping any. And again, I'm not seeing the smoke everytime I start the engine or everytime the rpm's get raised from idle. That, too, comes and goes. So, can anyone help me put this together and help me figure out where to look? I have a digital voice recorder that I can get a clip of the engine doing it's thing to help you hear the problem if that would be of any help.