Small Engines (Lawn Mowers, etc.): Smokin Kohler CV740S 27 HP Twin, twin cylinder engine, fuel air mixture

Question
Hi Ben Need Help! I have a 2003 GT6500 Craftsman Garden Tractor Powered by a 27 HP Kohler Command Vertial Shaft Twin cylinder engine Model CV740S Spec CV740-0018. Engine has 170 operation hrs. I noticed over the past year on occasion when parked for post clean up after lawn mowing, when restarted warm a puff of oil smoke would occur out the exhaust. During operation today and once previous, after warm up the engine produces oil smoke and continues thruout the operation period.  Today it consumed approx. 3/4 qt of oil over a 2 hour period of operation! To be sure proper oil level has always been kept with oil and oil filter changes a minimum of twice a year. Air filter, precleaners and fuel filters are cleaned and/or replaced several times a year as required. Engine is blown off with clean dry air after every use removing any grass and debris. Even removed air shroud for inspection and found it to be clean last year. In short it has been well maintained. Engine starts and has runs well but I feel like a smoked ham after running the tractor today! I researched the Kohler service manual for possible problems with the breather/s and maybe the pulse fuel pump possibly drawing oil from the crankcase yet not much info is provided in the factory trouble shooting section on engine smoking. Unsure of what I have. The oil collector cannister is quite wet with oil however inside air filter induction and carb area appear normal. Any ideas? Suggestions?     
Please advise
Best Regards
Chuck Nauman
Muskegon, MI  

Answer
Chuck

For the most part, smoking is just as bad for a small engine as it is for you. Excessive smoke from the engine may be an indication of problems with the carburetor, rings, or gasoline:

Black smoke is a symptom of an overly rich fuel-air mixture. This could be caused by a choke that is partially closed, a faulty carburetor, or the need for a carburetor adjustment. Make sure the choke if fully open. See the sections on carburetor adjustment and carburetor cleaning.

White or black smoke may also result from yard debris, oil, or other contaminants on the exterior of the cylinder as the temperature after a few minutes of operation will reach several hundred degrees F even with proper cooling. Stop the engine and let it cool for a few minutes. Then, check around the cylinder, cylinder head, and under the shroud for grass clippings, leaves, oil or other spills, dead rodents, etc.

2 stroke engines will always produce some fine white/blue smoke since the lubricating oil in the fuel mixture is being burnt along with the gasoline. However, excessive white/blue smoke could indicate an incorrect ratio of gasoline to oil or a mixture which has been sitting around for a while - the more volatile gasoline evaporates leaving behind the oil. It could also be an indication of contaminated fuel.

4 stroke engines should produce virtually no smoke while running. At first startup of the season, there may be a few seconds of white/blue smoke resulting from the oil squirted into the cylinder at the end of last season (you did the preventive maintenance, right?) burning off as well as white smoke/steam from accumulated moisture. If you tip the mower on its side routinely (to clean out grass clippings, for example), oil may seep into the cylinder resulting in white/blue smoke at startup as well.
White or blue smoke while running may be an indication of an excessively worn cylinder or rings or a clogged or inoperative breather (the breather assures that there is always negative pressure in the crankcase - if not, oil can get forced up into the cylinder). Or, you may be using the fuel mixture for your 2 stroke weed whacker by mistake!