breather hose RE routing ??

22 replies to this topic
  • aj_yz426

Posted March 01, 2009 - 07:52 PM


yeah, put up a how to on the catch can with pics. I have seen them done with turkey basters but never an rubbing alcohol bottle.

This probably should be in some other thread (sorry I'm a newbie here so not sure on protocol:smirk: ). I read about this somewhere here (can't find link now), but I don't recall a picture so I'll post my version. Have used this setup on other bikes in past, just installed on yz426 this winter and haven't tested in hot weather yet ( I hope it holds enough volume for the overflow from the yz426). If you ride tight/slow singletrack it prevents spilling coolant if it overheats. Vent hose out the top side is important otherwise you risk hot coolant exploding near your face. When the bike cools, coolant gets sucked back into radiator. I don't keep any coolant in the catch bottle otherwise. Rubbing alcohol bottle fits snug behind number plate without any fasteners.

Stock radiator overflow hose is used, but I cut the very tip at an angle so it doesn't get pressed shut at the bottom of the bottle. Gasket for cap made with piece of rubber cut in circle (can find in plumbing section of home depot to make rubber gaskets or use old tube etc.). I drilled hole in cap just smaller than the tube to force it through and get a good seal. Poked a hole in upper side of bottle and pushed a piece of tubing through there to provide an overflow vent so the bottle will not explode from pressure.

top view. I let the tube stick out alittle so I will see when coolant is flowing and I'm overheating:
Posted Image

thats where she goes, just slap the numberplate on and it holds it in place. notice vent tube in upper left of bottle:
Posted Image

vent tube exiting behind plate by left fork leg:
Posted Image

cap and gasket:
Posted Image

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  • grayracer513

Posted March 01, 2009 - 10:54 PM


Thanks, I'll include that one into the filter foam as well. Does the valve that opens with the allen bolt left side of carb bowl just let air in so the gas can drain out that tube? I thought it was to drain the float bowl instead of opening the big plug at the bottom. Now that I look at the diagram in the manual I see the standpipe part.

Sould I even worry about the carb hoses? Do you really think the carb can make enough negative pressure to suck anything up the vent hoses to begin with? I was more concerned with the oil breather hose since that could suck up 426cc's of water if trying to start the bike while the tube is submerged.

It's simpler than that. The drain bolt closes off a passage that leads to the bottom of the float bowl. This passage tees into the same one the standpipe does in order to make use of the overflow hose as a drain tube.

Under most normal situations, the fuel leaving the bowl is replaced by fuel coming in, so changes in atmospheric pressure within the bowl are minor and transient. That means for the most part that there isn't much air flowing in or out of the bowl. The exception is when operating with the choke open. The air for the starter circuit comes from the bowl instead of the carb intake, so it has to enter through the bowl vents instead of the air filter.

  • Wiz636

Posted March 02, 2009 - 02:19 PM


I have an 08 and since I was planning on using it as a track and trail machine this mod was on the to-do list. I didnt realize how important this really was until I pulled the valve cover off to check the valves today. 3 hrs on machine, 2 rides at the river and one short track ride. Valves of course are fine and there was an incredible amount of sand in the chamber around the breather! :p This mod is next and filters will be used.

I pulled my cover off the other day to check my valves and found dust on my head too,valves where ok.I only ride track,seems like a bad design to me:bonk:

Yep, same thing happened to me on my '06 (I took preventative measures on my '08 before riding it). There are people out there that insist it is impossible to suck dirt up the breather except only under very specific circumstances, i.e., the breather is buried under sand while kickstarting like if you were parked on top of a dune, but the fact is that dirt gets up there.

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