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Discussion Starter #2
I was told that it is a performance modification which reduces the air pressure in the motor, for the pistons to move easier.

Now I dont know how true it is???
 

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Why did Arata have to stop making exhausts :(

Some people run a line like that to help oil their clutches, but it is mostly worthless for that purpose.
 

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Usually that type of set-up is connected up top to the anti polution air injection at the exhaust port. In its stock configuration it injects filtered air from the air box to the exhaust ports to help fire off any unburnt mixture thus reducing unburnt hydrcarbons on trailing throttle-making your kwacker more eco friendly. You can (as in the photo) run a breather line from any spot on the crankcase plumb it to the exhaust port anti pollution system and the high velocity in the exh ports creates negative pressure which helps to "unload" some of the pumping loses in the crankcase. And yes theoretically the pistons should rise and fall easier, making your motor happier to produce more hp. If your motor isn't worn out (ie, good ring seal) and of stock cc's the original breather system should be adequate. Big cc motors or motors with cylinder leak down will be the ones that benefit mostly from this type of secondary breather.
 

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But, why not route it to the breather outlet on top of the crankcase the way it's usually done? That connection point has a separator to keep the liquid oil in the crankcase.

Going straight to the filler cap seems like an invitation for oil to splash out into the suction hose and lead to very high oil consumption. Maybe the length of the hose acts sorta like an oil separator. At a minimum, going this route just adds more complication to doing an oil change.
 

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The secondary breather is only effective when the engine has enough rpm to produce vacumm or negative pressure in the exhaust ports. That would be why this type of set-up is more common to a "race" bike than a street bike. Since the street bike must have crank ventilation at or near idle the stock vent routes to the air box to utilize intake vaccumm (and combustion) to rid the crankcase of fumes and pressure. But the performance minded street guy can benefit from this secondary breather when used in conjunction with but seperately from the factories primary breather. Back in the day of Z1 drag bikes (circa '73 to about '78) we would connect a hose from the original crank breather nipple to a bung 8 inches down stream of the collector to use the wot exhaust velocities negative pressure to evacuate the crankcase and eliviate its potential pumping losses. This was crude but effective, we didn't care about the bikes street function 'cause it never saw the street or part throttle usage. Todays bikes being much more sofisticated require a bit more sofisticated solutions. (excuss my spelling problems)
 

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The secondary breather is only effective when the engine has enough rpm to produce vacumm or negative pressure in the exhaust ports. That would be why this type of set-up is more common to a "race" bike than a street bike. Since the street bike must have crank ventilation at or near idle the stock vent routes to the air box to utilize intake vaccumm (and combustion) to rid the crankcase of fumes and pressure. But the performance minded street guy can benefit from this secondary breather when used in conjunction with but seperately from the factories primary breather. Back in the day of Z1 drag bikes (circa '73 to about '78) we would connect a hose from the original crank breather nipple to a bung 8 inches down stream of the collector to use the wot exhaust velocities negative pressure to evacuate the crankcase and eliviate its potential pumping losses. This was crude but effective, we didn't care about the bikes street function 'cause it never saw the street or part throttle usage. Todays bikes being much more sofisticated require a bit more sofisticated solutions. (excuss my spelling problems)
I've seen them before. It's a low buck mod that tuners have used for quite some time.
 

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I can't remember where I read it before, but it wasn't long ago. Someone did something similar to pump oil directly onto their clutch plates.
 
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