Breather tube

[jeeptrix]

There is a tube running to the front of the airbox from top of the engine. Can I plug this tube without adverse results?

[cberkeley]

Do not block this tube ....it vents the crankcase backpressure. The fumes from the crankcase are pulled into the intake and burnt in the combustion chambers.

[chef1366]

Plus if you plug it will blow out your gaskets.

[jeeptrix]

Isn't there a better way to vent backpressure? Is it really flammable?

[chef1366]

Did you lose your airbox for pods? They sell crankcase breather filters. Get one of these and run it to a place you won't mind a little dripping oil. Blow-by is not flammable. It will build up pressure in your crankcase if plugged and blow out gaskets.

[jeeptrix]

Let me understand this: the fumes are run back into the breather box to be recirculated into the carbs then into the pistons yet the fumes are not flammable. Why then are they routed back in the first place? OK, to relieve the back pressure but seems there has to be a better way.

[marvinsc]

Let me understand this: the fumes are run back into the breather box to be recirculated into the carbs then into the pistons yet the fumes are not flammable. Why then are they routed back in the first place? OK, to relieve the back pressure but seems there has to be a better way.

In 1979???:?

[Iceman71]

Jeeptrix,

this tube does the same thing on a bike that the Positive Crankcase Ventilation (PCV) valve does for a car....piston ring allow a small amount of cumbustion gases into the crankcase, causing a pressure build up, this is releived by allowing the crankcase to vent into the airbox, being assisted by engine vacuum. Another side effect is reduced emmisions (not sure just how effective this point was but hey they did the best they could back then...better then an old road draft tube..lol)...and they really are non flammable gases as such they help to lean your A/F ratio out thereby reducing emissions caused by overly rich mixtures on decel etc.
Hope this helps!

[jeeptrix]

thanks. guess I will leave well enough alone.

[Pharkmeh]

Jeeptrix,

this tube does the same thing on a bike that the Positive Crankcase Ventilation (PCV) valve does for a car....piston ring allow a small amount of cumbustion gases into the crankcase, causing a pressure build up, this is releived by allowing the crankcase to vent into the airbox, being assisted by engine vacuum. Another side effect is reduced emmisions (not sure just how effective this point was but hey they did the best they could back then...better then an old road draft tube..lol)...and they really are non flammable gases as such they help to lean your A/F ratio out thereby reducing emissions caused by overly rich mixtures on decel etc.
Hope this helps!

sounded a pretty comprehensive answer to meh too...

thx

Phark




:shock: so much to learn... so far to ride....

[demark]

Would putting in too much oil cause blue/white smoke at startup because of this tube?

I changed my oil and, not realizing it, put too much in. I then went for a ride. The bike then sat for a week. The next time I started her up, she smoked blue/white pretty badly for about 30 seconds. When I got home that day, I checked the oil window and noticed that I couldn't see the level because there was too much oil.

I loosened the plug and drained enough oil to bring the level to full (while the bike was upright on the center stand).

Since then, except for one instance of a short "puff" when starting, she's been running clean.

Would too much oil cause such an issue?

Thanks,
- Tony

[Iceman71]

there's a good chance you may be right, excess oil could have worked it's way to the top of the cam cover and through the tube while you're driving (which would end up back in the combustion chamber) or it may have been forced up past the rings. as long as it doesn't continue you should be alright..just keep an eye on it

[chef1366]

When you put too much oil in any vehicle the oil seeps in through the cylinders-pistons causing the smoke.

[tomcat24551]

Jeeptrix,

this tube does the same thing on a bike that the Positive Crankcase Ventilation (PCV) valve does for a car....piston ring allow a small amount of cumbustion gases into the crankcase, causing a pressure build up, this is releived by allowing the crankcase to vent into the airbox, being assisted by engine vacuum. Another side effect is reduced emmisions (not sure just how effective this point was but hey they did the best they could back then...better then an old road draft tube..lol)...and they really are non flammable gases as such they help to lean your A/F ratio out thereby reducing emissions caused by overly rich mixtures on decel etc.
Hope this helps!

There's another reason to pull the breather off the airbox occasionally: The fumes contain sulphuric acid and, especially in cold climes, the warm fumes will cause rust and corrosion when they condense in a cold metal airbox. Over several years, the rust can be bad enough to almost completely block the metal nipple at the top of the airbox.

If you've got a metal airbox, check it out--and clean it out!

[jeeptrix]

The airbox is plastic so I guess I don't have to worry. Besides I live in Arizona and it never gets cold here.

BTW what are "pods" that everyone refers to?