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I have a Tecumseh HM80 on a Troy Bilt Horse tiller. It is the second engine installed about 10 years ago. It probably has 75 hours on it. With clean fuel, correct clean 30w oil to proper level and clean crankcase breather, the engine runs fine with no exhaust smoke for 15 or so minutes then I get a huge cloud of white smoke that could hide a house. I have seen discussions of this on the net and people usually say "worn engine". If this were a worn rings-bad valves issue, wouldn't the engine smoke all the time and wouldn't the smoke be blue? Anybody have any thoughts on this?
 

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If it were blue smoke, I would have said you are burning oil. If it were black smoke, I'd have said you were burning too much fuel. White smoke is smoke of a different color. [heh] That said, I have heard that too much fuel can do white smoke, but I don't know how. I would check the crankcase ventilation system. There is a check valve on some engines that allows air to be pulled into the crankcase from the intake manifold, but if the valve were to be clogged or gummed, it could allow vapors from the crankcase to be fed to the engine. Older engines had 'draft tubes' that hung down on the side of the engine ventilating the crankcase. There was a check valve behind the rectangular plate the hose was connected to, directly over where the valve springs reside.
Anyway, I'd check crankcase ventilation for problems.
tom
 

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white usually indicates some kinda of water got into the system,
 

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It almost sounds like the oil is over filled, and it sis sloshing around. and a large amount is getting up into the combustion chamber.
 

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Have you tried increasing the viscosity of the oil to see if it helps? I still preach the ills of unleaded & especially E-gas. Did this phase in gradually, or make a sudden presentation? I have had ring to ring land clearance & piston to bore clearance in air-cooled engines drilled into me until I'm a believer. Excessive ring to land clearance aggravates blow-by & heating of the oil. Excessive piston to bore clearance robs the piston of most of its cooling & passing that heat into the oil. I know that the two-stroke racing boys who ran loose piston to bore clearances seized a lot more engines than the ones who held to the lower end clearance. For a cheap try, I'd use some Lucas oil treatment to help with viscosity & surface tension. I might try some Marvel Mystery Oil if the onset was rapid, as it might mean gummy/stuck rings. I never made a living working on small engines, as many here have, but I have kept motorcycles alive for a while. Oh yeah, have you heard that the EPA has forced the removal of Zinc from motor oils? This & the removal of Phosphorus compounds accelerate wear in high pressure sliding contact wear areas (cam lobes & flat tappets). Doesn't the EPA give you a case of the warm fuzzies?
 
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