Water In The Oil

I Have A 1999 Yz400f,the Problem I'm Having Is Everytime I Ride Thru Water It Gets In The Motor.i Do Ride Thru Some Deep Water.my Oil Will Be Milky When I Go To Change It.is There Anything I Can Do To Stop This.

Do you ever stall and/or resart while the crankcase breather tube (tube connected to the valve cover) is under water? If yes, then this is likely how you're getting the water in the motor. You may want to re-route it to the airbox or somewhere else that will stay dry.

Another way to reduce the likelihood of drawing water up the breather when stalled is to add a 'T' to the line that runs from the cam box to the frame. Run a hose from the 'T' up and into the steering tube with the gas tank vent. What this accomplishes is a vent to break the vacuum that forms in the breather tube, which will help stop it from drawing water.

Is This A Common Problem With These Bikes

Yes. With the engine running, it normally isn't a big deal, but when cranking, or possibly at very low idle speeds, the engine can draw water all the way into the engine.

Realize what's happening. The breather provides a link to the outside air to relieve the pumping pressure and vacuum that forms as a result of the piston running up and down in the bore (it displaces 400cc below the piston, too) and as a way to prevent the build up of pressure from blowby gases. When the engine is running, there isn't enough time to move the whole 400cc in or out of the tube before the piston changes direction, so it doesn't build up enough vacuum to raise all the weight of a column of water that far. But when the engine is being cranked, there is time to raise the water that far. The piston goes down, pushing out 400cc of air. When it goes back up it tries to draw 400cc back in. Since the tube has something like a 175cc volume, you can see the problem.

Air is springy, though, and a considerable vacuum is "stretched" in the tube to lift the water's weight. That's were the T in the vent line comes in. It allows air in from somewhere else to break the vacuum. Long time TT'r Wrooster used to deal with this by simply cutting a small, angled slit in the back side of the breather tube about even with the cam box gasket. And, of course, routing to the air box works, too.

Thanks For The Info I Will Try To Rerout It To The Airbox,and Also Could Water Get In Thru The Carb Vent Tubes

Thanks For The Info I Will Try To Rerout It To The Airbox,and Also Could Water Get In Thru The Carb Vent Tubes
Not very easily, since there is really very little vacuum or air circulated through them. They all end, atmospherically, in the float bowl one way or other, and the prevent the formation of a pressure differential between the mouth of the carb and the bowl, which would, if it were to occur, interfere with fuel being correctly metered through the jets. In practice, the vacuum caused by fuel leaving the bowl is mostly corrected by the fuel entering the bowl past the needle seat, but the occasional correction is needed, too. At least one of the lines connects to a stand pipe in the bowl that is intended to limit how high the level can rise in a flood situation. That particular vent line, located on the bowl itself, along with the drain should not be routed to the air box. As with the 'T' in the oil tank vent, only one of the lines that vent into the bowl need be kept above water to prevent a vacuum forming in the bowl.

In routing the crankcase breather to the air box, something neat that has been done is to utilize one of the small filter fittings used to connect an automotive PCV vent line to the engine's air filter housing. Remove the filter itself and cut away any unnecessary material. Then, cut a small hole in the air boot near the top and glue the fitting in from the back side, so that the nipple for the hose sticks out forward. Rotate your breather 90 degrees and cut it to fit. This puts the breather on the clean side of the filter element for a little more protection.

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