I did not read where you had changed the crankcase oil after the new carb was put on. If the old carb had been leaking there would certainly have been a quantity of gasoline in the crankcase oil. What happens is that when the engine is started with gasoline in the crankcase oil, after the engine begins to get warm........the gasoline begins to boil out of the oil. The evaporated gasoline then vents out through the intake manifold carrying a mist of oil with it. This oil laden mist is then burned in the combustion chamber. This scenario has been repeated countless times. If ever your engine gets gas into the oil this will occur. In addition to the new carb did the "tech" suggest that you need to install an inline fuel cut off valve and shut the valve off except when you are actually using the machine? Having an inline cut off valve and using it consistently is the ONLY way to ensure you never have this issue again. Even after you change the oil (and filter if equipped) you can expect some smoke for a few minutes until all the residual oil is burned out of the exhaust system.

Some of the "logic" being used by OEMs in the present time almost seems illogical to me. When the "standardized parts" concept replaced the "custom fit parts" method, it became much faster and cheaper because assembly personnel with little or no mechanical skills/training could be utilized instead of master machinists. In the present time, robotic equipment is able to do many of the operations that once required a human eye and hands. As OEMs try to engineer and tweak every step in every procedure to consume the least amount of energy and produce the smallest amount of left-over or wasted material in one part of the production sequence, they risk having more "rejects" or unsuitable parts. Applying the "custom fit parts" concept can allow parts that might otherwise be rejected because they could not be machined to a specific standard...........to still be used (instead of being tossed out). The manufacturing of a crankshaft is probably the most expensive process an engine OEM must deal with. The desire is to be able to get as many castings or forgings of crankshafts as possible from the least amount of raw metal. In a given "run" of casting or forging, you can expect to have some examples that would be rejected because the rod journals did not "clean up" at the standard diameter. By utilizing the custom fit method, the crank journal can be further machined to a smaller diameter and the connecting rod for that journal can be undersized. Using robotic equipment for the process makes this work with a degree of certainty that could otherwise be attained only by a highly skilled/payed machinist. But this method produces assemblies which must be kept intact as a matched set in order for the concept to be practical for the OEM. I was recently "educated" on the aim for increased application of robotics in industry when I ordered some instrument panel "lamp assemblies" (light bulbs in sockets) for our forklifts where I work. These lamps are proprietary to the OEM and the OEM parts division is our source for them. The bulbs are about the size of a "tic-tac" candy mint, in other words, small. Down through the years, I have always ordered the bulbs as a "10 pack" and the size of that 10 pack was close to the dimensions of a deck of cards. Well, the last batch of bulbs I ordered (as a 10 pack) arrived as 10 individual cardboard boxes that measured 1.25" X 1.25" X 2.5". Each box held 1 bulb, all wrapped up in a roll of cushioning foam. I called the parts dept at the dealer and asked what the heck was up with the new style packaging. His response was that the OEM parts division had a new warehouse and distribution center..........and all the stocking and "picking" of parts is done with robotic equipment and the carton is sized to fit the robot "fingers". All this to eliminate a human worker. And this is only the tip of the iceberg.

I take it the warranty out by years? IMO that's why they put time limits cause they know most people won't put to many hours or do any maintenance on or in two years. When it won't start that's when you need to troubleshoot it. IMO first I would do would pull the plugs see if you getting fire at the plugs (pretty blue spark, no orangish and of course no spark) It you got spark spray carb. cleaner down the spark plug holes and see if it will start up on the carb. cleaner. If it fires of the carb. cleaner and dies you still have carb. issue or compression lost. I afraid you going to have to take the heads off and look in the comb chamber at the cylinder walls, valves and head gaskets. seems like your problem occurs after the engine heats up and of course that would be the ideal time to take compression when it quits also. my guess would be cracked head, or something causing it to loose compression, that;s why you need to take the compression when it dead, if you got 130 PSI or more then IMO the bottom end, valves are good but that IMO don't over rule the head gasket or cracked head. I would also take the cooling fin covers off and see if I see any sign of leakages before I go tearing it apart. there alot of engines that will fit Based on the shaft size and length Course it easier to get the same type engine (HP number not that important but hookups are. if they are the same then HP don't matter as long as it close to what you've got. Most problems with going with different brand are the muffler and starter setup and throttle cables arrangement and brackets and of course if it will fit under your hood cowl. For the price of honda you can get you another used mower. and fixing the old one if you can do it yourself would be the best choice money wise IMO.

Walt, Thanks for the quick reply. A service manual would be great; I'll email you. It was the exhaust valve that was way out of spec, so much that the valve cap came off! This tractor has less than 100 hours on it. When I saw that, I checked the rockers, pushrods, studs, etc. I've re-checked to lash several times after running the mower to ensure it stayed within spec. I have the intake at .004" and the exhaust at .006". The only thing I haven't done while testing is the gasket around the valve cover. If this were a car I'd check the carb further, but there is nothing to adjust on these B&S engines. Furthermore, I notice the throttle linkage does not go all the way to the idle speed set screw at the lowest throttle setting. Could I have a governor issue? Just seems unlikely it happens to pop up at the same time, right? Best, Michael.