Head Breather

i just picked up an 08 yz250f and i noticed that the head breather just runs down to the bottom of the frame and is open at the bottom. Isn't dirt going to get into my motor.

It might but.... it is a long tube, it tends to expel blowby rather than suck in.

Race bikes (YZ) are always the minimal. WR's breather into the airbox.

If you boil over, it dunps coolant onto the ground. WR's use a recovery system.

This stuff adds weight.

Just curious, but doesn't air blow out of the hole, not allowing water to get into the breather hose. I have always had a light amount of air blowing out of the hose.

Erik

don't quote me, but I believe air is sucked into the hose when starting the bike. So never attempt to start the bike with the hose under water or in sand...

yup, i made that mistake in really deep mushroom dirt it was quite a mess but alot of it got cloged in the holes from oil residue

The air in the hose "pulses" with the movement of the piston. I did the "swamp proofing" mod and put small filters on each hose end because I found dirt particles in the valve cover.

The air in the hose "pulses" with the movement of the piston. I did the "swamp proofing" mod and put small filters on each hose end because I found dirt particles in the valve cover.

Yes, it pulses, but it blows out more than suck in when the engine is running. On a dead engine, it tends to suck in - so like DPW stated, don't kick the bike over if that hose is submerged in water, mud, or anything else, it will suck in.

Check out how I did my swamp proof mod. :applause:

Thats what I thought. It pulses is a good analogy.

Erik

its a PCV tube that comes from your head...it vents blow-by gasses (combustion gasses that get past the rings) away from your bike......at no point will this really suck in air, and believe it or not you get the most blow by gasses at idle than at any higher RPM.....no dirt will get in your motor but make sure its cleaned out often.

The air in the hose "pulses" with the movement of the piston. I did the "swamp proofing" mod and put small filters on each hose end because I found dirt particles in the valve cover.

What kind of filters. Is it like a small K&N cuz i think ive seen those before. I just want to do it to make sure and give me some peace of mind. Im not goint to be doing water crossing and things like that. Do you have any pics

Yes, it pulses, but it blows out more than suck in when the engine is running. On a dead engine, it tends to suck in - so like DPW stated, don't kick the bike over if that hose is submerged in water, mud, or anything else, it will suck in.

Check out how I did my swamp proof mod. :applause:

Hey Av,

the 2 hoses you refer to on your web site. What do they do? Do the just allow air to equalize in the carbie?

And to anyone with a WR, the head breather goes in to the air box, however if get water in your air box, as i did, the water will be sucked up and it turns oil milky.

So If you can re rout it higher its a good idea. But with all the stuff under the seat (battery etc.) its a tight squeze.

I found it easier to stick a smaller pipe into the hole in the air box where the head breather connects. This stops any chance of water entering the breather from the air box.

What kind of filters. Is it like a small K&N cuz i think ive seen those before. I just want to do it to make sure and give me some peace of mind. Im not goint to be doing water crossing and things like that. Do you have any pics
I think you could use the little plastic fuel filters for cars. I use these filters on my diff breathers for my 4WD.

The diff breathers are extended to the highest point in the engine bay behind the brake master cylinder (i think).... Much like the head and carbie breather I guess.

check out apllied racing...they make a trick little billet filter for this purpose.

http://appliedrace.com/store/catalog/product_info.php?cPath=8&products_id=1247

I ran mine up into and over the airbox and out the back by the rear fender. I put one of these filters on it just for good measure. my buddy sucked up a bunch of muddy water into his rmz and trashed his motor. cost him $1200 in parts. :applause:

it is cheap insurance just in case.

Hey Av,

the 2 hoses you refer to on your web site. What do they do? Do the just allow air to equalize in the carbie?

The 2 vent hoses from the carb allows the carb to equalize so that fuel can flow smoothly (i.e., engine won't die). If they are clogged by mud or if you're riding through deep water, then when the carb suck, it will get whatever those tubes are submerged in at that time. By splitting 2 of the vent tubes up high, you'll allow an alternative passage for the carb to breathe and your motor won't starve for fuel.

It's an easy mod and I don't know why they don't do this for all bikes from the factory. I've seen clogged tubes from mud (MX riding) and water in the carb from deep water crossings - it really should be done as one of the first mods on all bikes :applause:

The 2 vent hoses from the carb allows the carb to equalize so that fuel can flow smoothly (i.e., engine won't die). If they are clogged by mud or if you're riding through deep water, then when the carb suck, it will get whatever those tubes are submerged in at that time. By splitting 2 of the vent tubes up high, you'll allow an alternative passage for the carb to breathe and your motor won't starve for fuel.

It's an easy mod and I don't know why they don't do this for all bikes from the factory. I've seen clogged tubes from mud (MX riding) and water in the carb from deep water crossings - it really should be done as one of the first mods on all bikes :applause:

Sweet i'll do it tonight.

AV,

Your link says to take the two vent hoses from the shifter side and route them into the airbox. the old thumperfaq site said to take one from each side off the top tees and route those into the box. Although that was an older carb on the thumperfaq.

does it matter which ones?

AV,

Your link says to take the two vent hoses from the shifter side and route them into the airbox. the old thumperfaq site said to take one from each side off the top tees and route those into the box. Although that was an older carb on the thumperfaq.

does it matter which ones?

There are 2 openings from the upper part of the carb - one on each side of the carb. On the newer carbs, each opening will split off with 2 tubes on each side of the carb IIRC, each pair of tubes represents BOTH openings. So it is easier to pick the pair from the shifter side to route since the other side is more obstructed.

The idea is to make sure the 2 openings from the carb (from both sides) will have alternative passages so that the carb can breathe when you're riding through deep water/mud, etc. Not sure how old your carb is, but if you follow the pink hoses to where they come out of the carb, then take one side of the split from both carb openings and route them up high (like under your seat) then you're good to go :applause:

its a PCV tube that comes from your head...it vents blow-by gasses (combustion gasses that get past the rings) away from your bike......at no point will this really suck in air, and believe it or not you get the most blow by gasses at idle than at any higher RPM.....no dirt will get in your motor but make sure its cleaned out often.

That's correct, if there was a chance of it sucking in anything, Yamaha wouldn't just leave it hanging at the lowest point of the bike with no cover. It's called 'Possitive' crank ventilation for a reason.

That's correct, if there was a chance of it sucking in anything, Yamaha wouldn't just leave it hanging at the lowest point of the bike with no cover. It's called 'Possitive' crank ventilation for a reason.
I dissagree, why would Yamaha route the breather to the air box on a WR and not on a YZ? Perhaps they expect the WR to do more enduro type work?

Anyway I had milky oil due to water in the air box being sucked into the breather while the engine was cooling, same effect happens from a deep creek crossing, as the water cools the engine causing negative pressure.

Thats why 4WD's have diff, transfere case, and gearbox breathers... mine does anyway.

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