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crankcase breather into carb?

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I discovered something today that completely freaked me out:

 

that the crankcase breather expels dirty hot fumes unfiltered directly into the carb's air intake.

 

I have been confounded recently by engine bogging during rain riding and have torn into everything i can think of to identify the culprit. In the process, I noticed that the crankcase breather led directly intro the carb intake via a small opening on the left side of the airbox. This is just wrong I don't care who you are. 

 

Dirty hot air spewing into the carb is counter intuitive in terms of performance, fuel mileage and longevity.

 

So I detached the crankcase breather hose  at the airbox, attached an "L" tube and directed it toward the chain similar to a chain oiler, Then fastened it to the frame with some plastic ties so it would direct expelled oil to the top of the chain. Then plugged the opening in the airbox by inserting a rubber grommet into the airbox and held it in place with a small hose  clamp.

 

Wow, what a difference in performance. The engine runs noticeably stronger and I'd assume some increased fuel mileage as well. Wish I would have known this 25,000 miles ago....huh.

 

 

 

 

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Was pretty common on bikes which operated in real dusty/dirty conditions to have this done, as the breather can also suck air in occasionally.,

Or in a river crossing when it cools during a dunking, it can suck a large amount of water. Neither are good for it!

Perhaps stick a dust filter on the end if you're in harsh places.....

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I'm not going to sugar coat any response to that junk That junk just misleads people to doing things that could damage their bike or foul up a system that has been proven for decades. The only difference is the older bikes have a separate drain that yields about four tablespoons of splooge every oil change from the canister.

This site has a lot of good information; yours is not.

No dyno numbers, no reality.You haven't discovered how to turn lead into gold; alchemist.

Edited by Onederer

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Natey, the weak performance and excessive blow-by could both be symptoms of poor ring seal. There is nothing wrong with venting into the airbox when an engine is healthy, since the normal amount of blow-by is pretty modest. Once blowby flow is strong enough to push engine oil up the vent line into the airbox, your ring seal is pretty much gone.

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Natey, the weak performance and excessive blow-by could both be symptoms of poor ring seal. There is nothing wrong with venting into the airbox when an engine is healthy, since the normal amount of blow-by is pretty modest. Once blowby flow is strong enough to push engine oil up the vent line into the airbox, your ring seal is pretty much gone.

Agreed! The purpose of the breather is to do just that. Breathe. If your bike is pumping out an oily mist that is actually causing poor performance then you most likely have a problem. Time for compression and leak down testing.

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Natey, the weak performance and excessive blow-by could both be symptoms of poor ring seal. There is nothing wrong with venting into the airbox when an engine is healthy, since the normal amount of blow-by is pretty modest. Once blowby flow is strong enough to push engine oil up the vent line into the airbox, your ring seal is pretty much gone.

Agreed! The purpose of the breather is to do just that. Breathe. If your bike is pumping out an oily mist that is actually causing poor performance then you most likely have a problem. Time for compression and leak down testing.

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Natey, the weak performance and excessive blow-by could both be symptoms of poor ring seal. There is nothing wrong with venting into the airbox when an engine is healthy, since the normal amount of blow-by is pretty modest. Once blowby flow is strong enough to push engine oil up the vent line into the airbox, your ring seal is pretty much gone.

Agreed! The purpose of the breather is to do just that. Breathe. If your bike is pumping out an oily mist that is actually causing poor performance then you most likely have a problem. Time for compression and leak down testing.

Edit: i hate it when posts show up in multiples. I guess TT thought you needed to read my post three times...;)

Edited by Backwoods Bomber

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Edit: i hate it when posts show up in multiples. I guess TT thought you needed to read my post three times... ;)

 

LOL! I thougth it was tremmers from your hand shake!

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The crankcase breather alternately inhales and exhales the volume of air displaced as the piston goes up and down.  Every modern car vents the crancase into the intake too.

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The crankcase breather alternately inhales and exhales the volume of air displaced as the piston goes up and down.  Every modern car vents the crancase into the intake too.

well I got my ass whooped on this one huh.....haha. 

 

blow by.........don't think it's excessive since I don't use a lot of oil. The only reason I pointed it on the chain is because it was right there. 

 

running hot dirty air into the carb throat is a no-no for me. Because it's a common practice by manufacturers is not enough for me to think it's good in terms of performance, fuel economy or even longevity. They have other agendas to abide by , like EPA emission standards. 

 

Definitely runs stronger w/o the breather into the carb throat..........try it for yourself and make you own determination. Only takes a few minutes to do it.  

 

Given the possibility of sucking dirt/water in is enough for me to place some type of canister on the breather. I'm going to remove the rubber mouth end from the airbox drain tube and try it just to see how that works, but a canister would likely  be better. Either way, the crankcase breather will not go anywhere near the carb intake. 

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You shouldn't be getting very much oil vapor out the breather unless you have way too much oil in the engine, have significant blowby, or do a lot of high RPM entended running (like desert riding).  It's not really dirty air like an EGR system, it's just a volume of air equally displaced and then sucked in every time the piston goes up and down.

 

The 600R came with an open crankcase breather tube.  I thought the standard 650L power up mods had always been to disconnect the breather from the airbox.

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The 600R came with an open crankcase breather tube.  I thought the standard 650L power up mods had always been to disconnect the breather from the airbox.

i missed that if it did. I did Dave's Mods way back not too long after I bought the bike new in 02 if I am recalling correctly. If they did suggest this, Dave likely would have recommended a canister or whatever.  

 

Anyway, I just found a small cylindrical filter similar to a K&N and installed that on the end of the breather tube. This will become oiled naturally and breathe. It should resist also water similar to an oiled airfilter. 

 

I think on a big powerful bike, an auto, etc., the difference might be negligible. However, on a single cylinder like the xr650l, every little bit helps. 

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 I thought the standard 650L power up mods had always been to disconnect the breather from the airbox.

 

Exactly why this needs to become a joke just like powerband colors and blinker fluid. I even had some idiot tell me the camchain tension shaft on side of the head was a power device and that it could be turned to change the power; he was serious. I heard one XR650L that sounded like it was farting every time the engine was shut off because someone removed the canister and run one hose straight down and put a rubber valve on it, which made a fart noise as the engine stopped.

 

Now, unrelated to your post....

 

 

The XR600R did vent to the atmosphere, but it wasn't the same way as the single tube people are putting on their XR650L's. It had a T and one line went up near the front of the seat and the other line went to the bottom of the frame and had a rubber valve on it. There is not enough air movement in one direction to cause the heavier constituents to vent from the upper tube, so they are drawn into the T and fall into the lower tube and drain out. Those tubes are in the parts fiche below.

 

1996 XR600R:

 

H01740082.gif

 

The XL600R used the essentially (the side and bottom ports may be clocked different) the same canister as the XR650L except the XL600R hoses don't just route back into the crankcase from the bottom of the canister, the canister's bottom line on the XL600R is route away from the engine and to the bottom of the frame where there is a plug in it so it can be drained as part of regular maintenance. The difference is the XR600R one drains on it's on; onto the ground. Look at the line numbered 19 on the fiche below and the plug (23). It does attached to the bottom part of the canister, although it doesn't look like that in the fiche.

 

1984 XL600R:

 

HJ0906W0345003.gif

Now look at the XR650L. Exact same canister except the absence of a drain, it just drains back into the engine. Some hose rerouting and redoing can add the exterior drain function just like the XL600R. Tube 23 is where the drain is on the XL600R. Capping the T and running a hose with a plug to the bottom of the frame would add the drain function.

HM0713086001.gif

 

 

Now, a fiche from two more full on dirt bikes, clearly showing the crankcase being vented to the air box.

 

XR650R:

HJ500058.gif

 

2013 CRF450R:

 

HM0713061002.gif

 

 

Whatever the logic someone is using for removing the canister from an XR650L, the fact is NONE of the dirt bikes use a single hose routed upward for a reason. They all have a T with a lower hose and a plug or rubber valve. As far as PCV and EGR valves go, they are two things that help automobile engines stay cleaner (on the inside) and get better fuel economy. Simply removing parts from something isn't custom, cool or going to really make anything better and most often times will make things worse. Anyone who wants an oily mess on their bike, possible contaminant entry into the engine crankcase or for the engine to make sounds like air escaping a vagina, go ahead  an take the canister off and purify it with fire.

 

In the case someone wants to try something that takes a little thought and some actually know-how, this can be tried: http://www.teglerizer.com/triumphstuff/emissions/emissions_exhaustscavenging.htm

 

The above might be more of a benefit for those who are running big bore, high performance engines, the crankcase vent system on a stock engine is sufficient.

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Agreed, onderer, but I want to elaborate on the pvc system. A car engine has pistons going up and down at the same time, so there is no breathing in and out of the crankcase like a single cylinder. So all "positive" pressure comes entirely from blowby past the rings. Blowby, of course, is exhaust gas, and is loaded with water vapor. You don't want that condensing in the case, so it is fed to the manifold, where it is drawn out by engine vacuum. A healthy engine has very little blowby, so the fumes drawn in have no effect on the performance of the engine. When blowby becomes severe, it carries a lot of oil with it, which got dumped on the road prior to 1968 (or thereabouts) when the pcv valve rule went into effect.

 

The piston of a single moves air in and out of the crankcase with each stroke, but the big volume of air in the case and trans results in only a little air moving back and forth through the crank breather hose. Air pushed out of the case and back into the airbox is the same filtered air that was pulled out of the box on the upstroke. Again, a healthy engine has very little blowby, so air returning to the airbox will not be oily exhaust gas, and will not hurt performance. But heavy blowby IS exhaust gas, AND it picks up a lot of oil on its way out, and this nasty mixture will hurt performance. And that is exactly what I think is happening on Natey's bike.

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Onederer, thanks for the article on exhaust scavanging. Interesting stuff and it makes a lot of sense to use a system like that on something that is intended to have significant blow-by. With that said, these bikes are not intended to have that kind of positive outflow as a result of blow-by. This is why i would be concerned about natey's rings. It sounds as though the condition scott-m described is probably whats going on. I mean think about it, if everyones bikes had oily mist spraying into the air box the issue would have been addressed a long time ago.

Natey, others may correct me on this one, but in my experience blow-by as a result of worn rings does not always result in major oil consumption. Especially in the early stages of ring wear on a dry sump engine. However, a pressurized crankcase usually means bad rings and a compression test can confirm things really easily. I really urge you to check compression.

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Agreed, onderer, but I want to elaborate on the pvc system. A car engine has pistons going up and down at the same time....

 

Yes to the multi cylinder thing and some PCV stuff, I know that, but for the sake of this thread I didn't want to overdo it because it's not as relevant. Things like low tension rings and/or  artificial aspiration also make crankcase evacuation more of something that has to be addressed on race vehicles but isn't as relevant to street vehicles.

 

I follow what your saying. Ever hear stories about the old car blow-by tubes getting plugged with mud or dirt dabbers and the subsequent gasket leaks?

 

Backwoods Bomber is on the right track by suggesting the engine needs a compression test done. Without some real information, it's just pissing in the wind and seeing what comes back.

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I'm not going to sugar coat any response to that junk That junk just misleads people to doing things that could damage their bike or foul up a system that has been proven for decades. The only difference is the older bikes have a separate drain that yields about four tablespoons of splooge every oil change from the canister.

This site has a lot of good information; yours is not.

No dyno numbers, no reality.You haven't discovered how to turn lead into gold; alchemist.

 

sounds like you might had a bad day dickweed! 

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Agreed! The purpose of the breather is to do just that. Breathe. If your bike is pumping out an oily mist that is actually causing poor performance then you most likely have a problem. Time for compression and leak down testing.

 

 

there is no poor performance relative to breather deposits in the air box......runs good. Only during heavy rain the bike starts to bog. This was first caused by an electrical short that caused severe bucking during rain. Solved that issue. However this bucking caused the carb to loosen from the airbox rubber and suck water during the rain. Still waiting for the next downpour for further tests.

 

Anyway, in the process of finding the wet riding problem, i discovered the breather in the airbox thing. 

 

Since then, i blocked off the air box hole, routed the hose to the area above the chain above the CS and put a small filter on it. The bike is running better than before, and so far has improved fuel mileage(Two 150 mile runs used 4 tenths of a gal less than previously). Too early to judge for sure, but I will keep track of and report.

 

I did happen upon this article which I found interesting:

 

http://britcycle.com/Products/BunnBreatherKit/Bunn_Breather_Article.pdf

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You stated in your original post that there is dirty hot air spewing into your air box. You said you directed it at the chain so the oil coming out of your breather would land on the chain. You also stated a noticable increase in performance and fuel economy after removing the breather from the air box. In a healthy engine there should be no noticable difference in performance or fuel economy by disconnecting/rerouting the breather.

All i am saying is that if you have oily mist constantly coming out of your breather and you have noticable gains in power or mileage after removing it from the intake, you need to check your compression.

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