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Purpose of breather hose from top of engine?

  • Thread starter Thread starter ty998
  • Start date Start date
T

ty998

Guest
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? :confused:
 
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.
 
rustybronco said:
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.
Click to expand...

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.
 
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?
 
rustybronco said:
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?
Click to expand...

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.
 
rustybronco said:
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?
Click to expand...

It has been. And on THAT note... I'm headed out. Elvis is leaving the building, only to return again, tomorrow. :confused: ;)
 
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.
 
spchips said:
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.
Click to expand...
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".

.
 
The round Earth hoax, and science conspiricy?

The round Earth hoax, and science conspiricy?

Steve said:
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".

.
Click to expand...
Or, look for: idiot, PO, and previous owner. :p
 
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?
 
J2Bs said:
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?
Click to expand...

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.
 
J2Bs said:
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?
Click to expand...

The vapors can make a mess of everything over time. Since my bike doesn't have an airbox, I run my vent tube into a catch can, but I used to run it down behind the engine as a road draft tube.
 
Burque73 said:
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.
Click to expand...

when I got the bike the hose was connected to the engine, just not the air box. Engine an still breathe fine, just wondering if to add the hose also to the air box or just let it roam free!
 
Tom R said:
The vapors can make a mess of everything over time. Since my bike doesn't have an airbox, I run my vent tube into a catch can, but I used to run it down behind the engine as a road draft tube.
Click to expand...

Thanks Tom. Helpful insight.
 
Tom R said:
The vapors can make a mess of everything over time. Since my bike doesn't have an airbox, I run my vent tube into a catch can, but I used to run it down behind the engine as a road draft tube.
Click to expand...

Did you use a hose with a pinched end on it like the one under the airbox? Just curious is all.
 
J2Bs said:
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?
Click to expand...

There is a slight negative pressure in the air box that assists in scavenging. Makes the ventilation system more efficient and provides better ring sealing.
 
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