Small Engines (Lawn Mowers, etc.): JD 320 engine problem, rich fuel mixture, fuel nozzle

Question
QUESTION: I have a John Deere 320 Lawn Tractor I bought for 350, anyway, when you start it, it will blow black smoke, like it's flooding or something. and it is also sluggish running, almost kills the motor when the blades are turned on. where should I start? it is a FD590V 18 hp Kawasaki motor. any help is greatly appreciated

Sam
Tennessee


ANSWER: You're describing an overly rich fuel mixture.  A few things can cause this.  The most common cause is nothing more than a dirty air filter.

After that I'd move to the carburetor.  The choke could be sticking, an air circuit in the carburetor could be clogged, even the fuel nozzle could be allowing too much fuel to flow.  What I would do at this point is simply to rebuild the carb rather than try to chase down a specific carburetor ailment.  You should soak the carb in a cleaning solution. Spray cleaners are great for what they're made for, but they aren't so great at reaching into the tiny passages that dirt gets trapped in.  

If neither of these are the source, then you would have to look at the valves.  I doubt this is the problem though as you should be seeing other symptoms like a lot of popping back through the carburetor.

Try the above and let me know what you find.  If you have any questions or problems, just let me know.  Thanks, PK.

---------- FOLLOW-UP ----------

QUESTION: ok, I tried the air filter, it did stop black smoke, but it is in fact popping through the carb. Don't know if it does it all the time, but when I started it without the air filter I could really hear it, but only when increasing the throttle. Can't tell if it is doing it or not with the filer installed

Thanks abunch
Sam

Answer
You probably have two or three things going on at once.

I'd start with the carburetor.  I'd go ahead and rebuild it.  I would treat this occasion as a maintenance interval and do a complete service including adjusting the valves.  I believe your valve lash is set at .010".  I'd go ahead and replace the plugs if you haven't already.  Pay particular attention to the plug condition.  I imagine they'll be black and sooty.  After running the new plugs for 30 minutes to an hour, let the engine cool down and check them again.  If they're gray and scaly, you're running a little lean.  This can cause some backfire through the carb.

Your engine may have a plastic cam gear.  These have had some problems.  A little excess wear might cause your problem.  But before I started tearing into the engine, I'd be certain I had the carburetor and other maintenance issues covered.