breather hose question

Hi fellas, sorry for my ignorance, but I've got a few questions about the function of the cam cover breather hose on the riders left side of the Yamaha thumpers.

Does it suck all the time? My buddy, who does not yet have the breather rerouted on his YZF450 followed me through a 2 foot deep stream yesterday, and as he was riding away his bike stalled. Did he suck water into his engine, or is that only a problem if you stall in the water? He started it after a few kicks.

Also, which lines from the carb need to be rerouted to the airbox? Thanks


If you're talking about that one which comes from the cylinder head it doesn't suck at all. When idling you will actually notice air coming out from there. This air is caused by piston going down and "compressing" air in the lower engine. Also if you engine is very lose it will breathe thru here. Only place where engine sucks air is from airbox. The whole concept of "breather" hose is bit misleading

Timo Mc

So what is the harm with a bike stalling in deep water? I put my finger over his hose while the engine was idling and it seemed to just barely suck my hand to it. Is this normal?


No harm as long it doesn't take water from the airbox.

With some speed you should easily be able to drive water line almost at the seat level (with standard airbox).

If the engine is able to keep oil in, it will keep water out too :crazy:

Timo Mc

From what I understood, the breather may draw water in if teh bike is restarted with the hose underwater. More likely on a estart bike since you can hit the button withiut thinking.

Have a close look at the oil, if its mikly, it has water in it.

Air goes in and out from the breather as the piston goes up and down. My understanding is it only sucks water into the engine if you restart with the hose in the water.

I routed one carb vent from each side into the airbox and left the others alone. If all 4 carb vent lines go under water it can stall. It happened to me in the middle of a knee deep puddle :crazy: before I rerouted them.

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