L4600 kubota runs well and then over reves won't shut off with key much white smoke after stalling to shut off it takes about 15 min waite till it will start and run fine
I would check for a vacuum leak either under the carb. or, if it has an intake manifold as a separate piece from the engine block, check for a leak here. These could be loose, cracked or the gasket could be bad.The easiest way to do this is to have a can of carb. cleaner spray handy, expose the carb. by removing the air cleaner, start the engine and wait for it to rev. When it revs, spray the carb. spray at the base of the carb. and at the manifold, if it exists, where it connects to the engine. If either affects the speed of the engine, there's your vacuum leak. When metal is cold, it contracts in size. You said it revs after 15 minutes. When metal gets hot, it expands or, if it isn't cast properly, it can deform in shape allowing air to come in uncontrolled causing it to rev out of control but in a lean fuel mixture. When you stall it, depending on how you do it, the white smoke is probably liquid gas in the cylinder(s). If you put your hand over the carb. to starve it of air, you could be sucking some motor oil past the piston rings and into the cylinder. Make sure to check the oil level. Good luck..
