crankcase breather plumbed to carb ?

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older 10hp tecumseh engine hm100-159252L that's on a 5000 watt generator, horizontal shaft. the motor is typical 80's single cylinder and has breather tube sticking out side of block with 3" long black tube facing downward. the thing uses oil, and tends to make a mess on itself after running 5-8 hrs blowing oil vapor out the vent tube. I suppose it's mostly normal, the thing runs great otherwise. but i was thinking of putting a 5/16" barb on the vent tube and extending with fuel hose to the carb air filter cover so the carb pulls in the vapor and everything is cleaner. looking for thoughts if it's a good idea and what i should watch out for. i'm guessing i shouldn't plumb it air tight so it doesn't suck vacuum in the crankcase? should i drill a small hole in the upper part of the crankcase as an inlet vent tube?
 
If the oil gets on the air filter, an air filter not designed to be oil wet, that gets oil wet may act as a choke that is on when no choke is required. That could foul you plug, and running an engien rich all the time results in the extra fuel washing the oil from the cylinder wall, resulting in wearing out the piston and cylinder in a short time.
 
If it is like most Tecumseh engines, the breather tube is coming out of the valve cover. Inside the valve cover there is a reed valve. It acts like a PCV valve does on a car engine. The reed valve opens to let pressure out of the crankcase and closes to retain vacuum in the crankcase. Do NOT drill a hole in the crankcase! Engines are SUPPOSED to have a vacuum in the crankcase to help keep oil from blowing past the piston rings and into the combustion chamber. Most small engines have this plumbed into the intake between the air filter and the carburetor. If you want to do this sort of thing, this is the location that you want to use.
 
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Originally Posted By: lars11
shouldn't that tube go into the carb by design?

It does on most small engines, but not all of them. This was especially true in the old days, before anyone was worried about polluting the environment with small engines.
BTW, if the reed valve is stuck open or otherwise isn't working properly, it will blow a lot of oil out of the breather pipe and the engine will burn a lot of oil and smoke.
 
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I have an older 10 hp and the crank vent hose goes into the air filter. It's the old style foam filter. It puffs out some blowby smoke from the tube now and then, but runs like a champ.,,
 
here's a pic of the engine, part 172 and 173. i know what you are talking about about the reed valve thing. this doesn't have it, it's just a green nylon mesh filter keeping oil from free flowing out the breather vent
 
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the air filter i have is #245 and the steel cover is 250.
the air filter i wouldn't want oiled up, so i was thinking of drilling in the center of the cover so oil vapor would never get pulled through the filter paper, it would go through the center of it directly into carb.
 
My Kawasaki powered equipment all have breather hoses that go into the elbow before the carb. (between filter and carb)

I pulled one off and was surprised at the amount of blowby. It's a good thing to burn this off. With it removed, the engine ran exactly the same. I don't see any valve buildup either when the carb is off.

My carbs remain very clean and there is no trace of oil. So, clearly, the fuel keeps it clean.
 
1FMF, a new reed valve and screen cleaning in that breather box may help reduce the amount of oily smog belching she's doing.

Keeping the oil level no higher than mid-range helps too.

Yes, on the 'better engines', breather tubes are mounted downstream of the air cleaner element and just get drawn into the engine.
 
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