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Pressure comming out of crankcase breather?

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Im working on a 01 XR 250 for a friend. The bike is hard to start and when it does the idle is high and goes up and down. Cleaned the carb good and still does it. When i was kicking it i could hear some air comming out of the crankcase breather. When it runs you could feel air comming out.

Does that sound like a bad compression ring or a bad crank seal?

Thanks

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Got a compression tester ? Bad rings will cause that.

Compressed air is getting by the rings into the crankcase and out the vent.

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The crankcase vent moves air in both directions, in and out, as the piston moves from TDC to BDC in a normal stroke of the engine. That's normal. It's why it's called "a vent".

Air being pulled into the crankcase is one reason why we run the vent line up high and put a filter on it, rather than leaving it to dump out below the engine where dirt and moisture can be introduced thru it into the engine.

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I think he has more symptoms of bad rings then normal operation. Bad rings can also cause sporadic idle. Still voting for the compression test.

If an engine is damaged or enters old age, gaps can form between the cylinder walls and pistons, resulting in larger amounts of blow-by than the crankcase ventilation system can handle.

Ive never heard air coming out my vent.

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Ive never heard air coming out my vent.

I've never heard it either, but I felt it on my leg one time when i started my bike in shoes and shorts.

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Before you go doing a compression check, check/set the valves to spec..

Did you happen to take note of the carbs jetting when you cleaned it? How detailed of a cleaning job did you do? Did you clean the jets, fuel screw passage and check/set the float?

Check for damaged/flattened intake manifold gasket? Air leaks?

Vent lines clear?

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I agree with TR42, If the rings are bad causing excessive blow by, you would have smoke coming out of the vent.

I second the carb cleaning/check for air leaks.:banana:

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The valve adjustment was good Bob, Im gonna have to buy a compression tester adapter just for the 250

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I still think it sounds like an air leak or partially clogged pilot circuit.

Try running a piece of wire through all of the ports to remove the brown residue (not just spraying carb cleaner) because the spray will always leave something behind.

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I blocked off the air intake on the bike and instead of stalling it started racing, which means its pulling air from somewhere else. Any ideas, crankseals seem unlikely to me since its not all that old?

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I blocked off the air intake on the bike and instead of stalling it started racing, which means its pulling air from somewhere else. Any ideas, crankseals seem unlikely to me since its not all that old?

No, the air leak has to be on the intake! Between the slide in the carburetor and the head. The O-ring on the intake (17 SKU: 91302-KR0-003

O-RING, CARBURETOR INSULATOR (Honda Code 2413342) would be my first suspect. :banana:

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