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what is this air-intake part for?


armyofda12mnkeys
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So this part comes out of my engine and into the part of the air intake that 'meets' in the middle...

What is the purpose of this? (disconnected from air intake in this pic)...

thought air mixes with gas and goes into the cylinder via into intake valves straight from carb, but this seems to pull in extra air into the engine?

4744310952_0936eb4b7f.jpg

So i dont see it listed on the intake for my bike, I'd like to know what 'system' this part is considered as in (i checked carbs and air intake to no avail)

http://www.boats.net/parts/search/Yamaha/Motorcycle/1978/XS400E/INTAKE/parts.html

Thanks!

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That is the crankcase breather. This allows excess air pressure in the crankcase to be vented and any fumes are burned in the engine. It is supposed to be connected to the rubber intake that goes from the carbs to the air boxes. That intake has a crossover that connects the two sides together and there is a port for the breather to connect to on the crossover. If you overfill the oil, it will vomit out of that breather.

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this is on all modern internal combustion motors, it is there to allow air pressure inside and outside the engine to equalize, in cars the breather line comes out the valve cover most times and into the intake allowing any gasses formed by hot oil in the engine to be burned off making the engine cleaner yet the hot gases tend to reduce alil power as we all know the colder the air the more power, so on high performance engines mostlly V-8's you see a simple filter ontop of the valve cover to help condense any oil out of the gas and keep it in the engine and let the gas vent yet not ingest the hot gas to harm performance.

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That is the crankcase breather. This allows excess air pressure in the crankcase to be vented and any fumes are burned in the engine.

I guess my next question is, i bought some new replacement air filters, POD style. which would fit onto each carb ... but there wouldnt be a shared intake line anymore...

What to do with that black hose if i were to install them (i realized the 48mm xs400 filters sold on ebay are a realllly tight fit and just pop off since the outside diamter is 55mm and not 48mm... so going back to old aircases, but still wanna know for curiousity)? Think my friends newer bike has something that almost looks like a mini air filter instead of a line that goes into the intake, saw one that may fit xs400.

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Like Noah was getting at, go down to an auto parts store and find a small air filter that will fit that hose. You con't block it off and you don't want dust to be able to get in there. They are even called "breather filters". You should be able to find one that fits. If you are sure you are not going back to stock air boxes, you could cut the hose off a little lower.

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Like Noah was getting at, go down to an auto parts store and find a small air filter that will fit that hose. You con't block it off and you don't want dust to be able to get in there. They are even called "breather filters". You should be able to find one that fits. If you are sure you are not going back to stock air boxes, you could cut the hose off a little lower.

cool thanks, I was just curious. prob keeping my stock boxes

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I'd stick with the stock air system, I hear if you go to the pods you have to re-jet the carbs since the engine is getting so much extra air. personally just a hassle I'd rather not deal with besides I rather cruise then scream along and the bike stock has plenty of pull.

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interesting you posted this cause I just got an Xs400 from some sketchy guy..

and I noticed he had the hose from the carb capped with a double a battery

and the hose connected to the engine was a 2ft long vinyl tube that ran to the bottom of the bike and

was just left open. I removed it the other day and hooked it up the way its supposed to and everything

still seems to function ok like it did before.. but I haven't really got to ride it around for long.

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  • 2 weeks later...

interesting you posted this cause I just got an Xs400 from some sketchy guy..

and I noticed he had the hose from the carb capped with a double a battery

and the hose connected to the engine was a 2ft long vinyl tube that ran to the bottom of the bike and

was just left open. I removed it the other day and hooked it up the way its supposed to and everything

still seems to function ok like it did before.. but I haven't really got to ride it around for long.

Im curious, can you get gas in your engine through that breather tube?... like if your petcock is accidentally left on prime, and the floats get stuck, and gas is overflowing and going into the airbox and it goes in the middle tube into the engine?

Just trying to think theoretically if it can happen and maybe just buying one of those crankcase breathers is a better option

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Im curious, can you get gas in your engine through that breather tube?... like if your petcock is accidentally left on prime, and the floats get stuck, and gas is overflowing and going into the airbox and it goes in the middle tube into the engine?

Just trying to think theoretically if it can happen and maybe just buying one of those crankcase breathers is a better option

Showing my age to a degree here but most of the old brit door stops, sorry vintage classics had a piece of garden hose running from the engine breather, routed right to the back of the bike behind the number plate to vent the gasses.

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Showing my age to a degree here but most of the old brit door stops, sorry vintage classics had a piece of garden hose running from the engine breather, routed right to the back of the bike behind the number plate to vent the gasses.

Yep, and cars had what some called a "breather cap" on top of a metal tube coming up from the crankcase. That was before we decided to "recycle" the crankcase gases. Al Gore probably claims to have invented that too! :P

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