Purpose of breather hose from top of engine?

[ty998]

Bike: '81 GS650 G

What exactly is the purpose of the hose that runs from the top of the engine to the airbox? I realize that it is the "breather" hose. Why would the engine also need to breath from this hose as well?

[Agemax]

that is the ONLY breather on the engine. stops internal pressure build up inside the engine

[7981GS]

Crank case evacuation.
Emissions.

Eric

[rustybronco]

It is to allow the 'crankcase vapors' to be introduced into the intake stream, so they can be burned in the combustion chambers instead of just being vented into the open atmosphere like you would have with a road draft tube. Think of it as an emission reduction system.

[Dave8338]

______________________ ______________________

[sedelen]

It is to allow the 'crankcase vapors' to be introduced into the intake stream, so they can be burned in the combustion chambers instead of just being vented into the open atmosphere like you would have with a road draft tube. Think of it as an emission reduction system.

It's there to introduce dirty oil vapors, acid, and whatever else your engine holds back into your air box to foul out your carburetors, at least that's how I see it. Ever look inside your airbox and see all the crap that's built up from it? Sticky and gooey, and since it's attached to your air box, the carb suction is literally sucking out all that vaporized stuff from your engine and feeding it back into the carbs. I believe they call it positive crankcase ventilation.

[rustybronco]

Steve, I didn't use the word positive because there is no metered orifice connected to ported vacuum. The method used is a bit more hit and miss than the PCV systems used on a vehicle.

Dave... that rough of a day eh?

[sedelen]

Steve, I didn't use the word positive because there is no metered orifice connected to ported vacuum. The method used is a bit more hit and miss than the PCV systems used on a vehicle.

Dave... that rough of a day eh?

You're the man Dale! if it did have a metered orifice it would probably get clogged all the time, like the one on a town car I used to have did.

[Dave8338]

Steve, I didn't use the word positive because there is no metered orifice connected to ported vacuum. The method used is a bit more hit and miss than the PCV systems used on a vehicle.

Dave... that rough of a day eh?

It has been. And on THAT note... I'm headed out. Elvis is leaving the building, only to return again, tomorrow.

[spchips]

There is another.......

Hole, under the starter cover, excellent for trapping spilt gasoline and pouring it into the engine. This would be the air intake hole. Air comes out the top from the vacuum of the intake.

[Steve]

There is another.......

Hole, under the starter cover, excellent for trapping spilt gasoline and pouring it into the engine. This would be the air intake hole. Air comes out the top from the vacuum of the intake.

There have only been two holes under any starter cover that I have opened.

One is the perfect size to hold the end of the starter motor, and is usually filled with one. The other is at the bottom, and actually goes straight to the bottom of the engine. It is only a drain for the starter cavity, it does not go into the crankcase at all. You can find several references to it in the forum by doing a search for "mystery hole".

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[Buffalo Bill]

The round Earth hoax, and science conspiricy…

There have only been two holes under any starter cover that I have opened.

One is the perfect size to hold the end of the starter motor, and is usually filled with one. The other is at the bottom, and actually goes straight to the bottom of the engine. It is only a drain for the starter cavity, it does not go into the crankcase at all. You can find several references to it in the forum by doing a search for "mystery hole".

.

Or, look for: idiot, PO, and previous owner.

[ikantbreave]

Or, look for: idiot, PO, and previous owner.

That's usually under "@$$hole", not "mystery hole"

[J2Bs]

Sorry to hijack this thread. Reading he replies, my question is: is there any benefit (except environmental) to having the breather hose attached to the air box, instead of just being disconnected?

[Burque73]

Sorry to hijack this thread. Reading he replies, my question is: is there any benefit (except environmental) to having the breather hose attached to the air box, instead of just being disconnected?

Disconnected and what, capped? Post #2 mentions the pressure build up in the engine. That pressure build up has been mentioned in other threads as a possible cause of oil leaks elsewhere on the engine.