Hello Jim here and I'm a newbie. I found this forum earlier today on my first attempt to gather intell on a problem with my Kawasaki fc420v. It looks like a very informative site if one can learn how to navigate and search it for a specific item. I'll just jump right in by addressing two issues, but first, a little polite etiquette. Thank you in advance for any and all help and suggestions offered. Now, item 1) my area of above average understanding and limited experience, is in electrical. I don't have any small-engine shop experience, just good practical common sense and training/experience years back, in component-level TV, radio and alarm system repair and service. 2) My reason for seeking help in the first place is as follows: My 8(?) year old Kubota with a 14 HP Kawasaki fc420v is "loading up" which is the term I believe I have heard used. It starts and runs fine, but when the power is called on, as in cutting grass, it sounds some how like it is laboring. Also, it blows black smoke out the muffler dense enough to see but not startlingly thick, also under load. In fact, the worst smoke occurs as the blades are being slowly engaged.Then, when the ignition is turned off, as the engine dies it backfires, also through the muffler and blows out a puff of black smoke and a lot of soot. It does this almost every time. The plug has recently been replaced and I bought a new air filter for it today so I will try it tomorrow and see if it makes a difference. What I really think it needs is to lean out the mixture. I do not know how to adjust carb. if in fact that is what needs to be done. The spring loaded screw that I would think most likely to control the fuel mix, has a plastic "stop" on it to prevent anything other than very slight adjustment. Does anyone care to offer advise? Again, thanks in advance for the help.