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My bike is blowing oil out of the vent tube, - 2004 Honda Xr 250

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Either you have over filled the oil or the crankcase is pressurising due to blowing past the piston rings or valve seals

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Posted on Jun 03, 2010

  • benl1107 Apr 21, 2011

    How do I check if the crankcase is pressuring



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My new crf 150 is blowing oil out of vent tube rode 2 hours and oil is barely on stick any ideas?

Sounds like it has NO OIL!!!!
The 'vapour' is just that, oil vapour from crank-case.
If the 'Stick' is the 'Dip-Stick', put some oil in it (till it reads the correct level).
Good Luck with it.
For more Bike stuff, go to YouTbe/CrashTestDummyTV

Aug 22, 2015 | 2014 Honda CRF 150R

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Oil coming out of crankcase vent tube

I'd quicker think piston ring blow by the piston thus compression leaking / blowing into the engines base.

Mar 01, 2014 | Motorcycles

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Crankcase blow

too much oil, too much time reverse, or bad ring.

May 01, 2013 | Pit Bike 125cc 4 Stroke Dirt Bike

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Ttr50 oil blowing from vent tube

Hi, Lee oil level readings are taken when the engine has reached normal operating temperature and the usual suspects are:
1. Overfilled oil tank dipstick reading should at or below full.
2. If the sight glass is full you are running to much oil.
3. Excessive blowby caused by worn out piston rings.
4. Piston rings never properly seated.
5. Faulty breather valve or system.
6. Pinched or clogged breather line/hose.
7. Clogged or failed oil filter.
8. Contaminated oil dirt-rust-water etc.
9. Excessive oil foaming.
10. Wrong oil type not designed for your bike.
For more information about your issue and valuable "FREE" downloads that you will need please click on the links below. Good luck and have a wonderful day.
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Sep 24, 2012 | 2010 Yamaha TTR50E

1 Answer

When i start my 91 ultra oil comes out of the vent filter under center of bike. Just started doing this after sitting 2 months,

Regrettfullly, this is a common occurance on any H-D motorcycle in which the oil tank is mounted higher than the oil pump. When the bike is allowed to sit for a while, the oil will seep past the check ball valve in the oil pump and build up in the engine. Harley changed the oil pump in their 1999 and later Twin Cam engines because of this. When the oil settles in the bottom end, we call it "oil sumping". When the engine is started, the scavenge gears simply cannot pump the oil back into the oil tank quickly enough and some of it is blown out the crankcase vent tube. Make sure that when your bike sits for a long period of time, do not add oil to the tank as long as you can see the oil level on the dipstick. If the oil checks a bit low, it may be in the engine cases. If you "top it off", it'll blow it all out the crankcase vent. Once the engine clears itself out, this should stop. If not, you'll have to have the check ball "reseated" in the oil pump.

Good Luck

Aug 22, 2011 | Harley Davidson FLHTCUI Electra Glide...

1 Answer

Oil is blowing out of tube into filter housing on my 89 Harly soft tail. Bike hasent been started in there a check valve? Any info. Thanks.

Yes there is a check valve but it's in the oil pump. This is a problem with the pre-2000 Softails. The oil tank is mounted higher in the frame than the oil pump on the engine. When the bike is allowed to sit for an extended period of time, the oil seeps past the check valve ball in the oil pump and settles in the engine cases. We call this "oil sumping". When the engine is restarted, the oil pump scavenger gears simply cannot pump the excess oil back to the oil tank fast enough and it is blown out of the crankcase vent tube. Since the EPA requires that vented crankcase pressure be cycled through the engine to be burned, the crankcase vent tube is connected to the backside of the carburetor backing plate. There are baffles in the tube but they only work for oil mist. The results is that your air filter gets filled with oil when you restart the engine after a lenghty downtime. Most riders will disconnect the tube from the backside of the backing plate and plug the hole in the backing plate. Then they install a simple hose about six inches long or so to the nipple that comes out of the engine cases and run it back towards the rear of bike underneath it. Some guys will put a small crankcase breather on the end of the hose as well. This way, the oil will go on the ground and you can clean it up. I usually slide a shallow pan under the bike before restarting one that has sat for a while. Avoid "topping off the oil tank" before restarting a bike that has sat for a while. Check the oil level and as long as the oil is visible on the dipstick, restart the engine and check the oil level when the engine reaches operating temperature. Harley improved on this problem in 1993 when they went to the "head breathers" where the crankcase vents are located in the cylinder heads.

Good Luck

Aug 21, 2011 | Harley Davidson FXST Softail Standard...

2 Answers

My dirtbike runs and idles fine but as soon as i get down on it it blows all the oil out through the big breathing tube under the seat! What might be stopped up and How do i clean it?

The breather tube is there to eliminate a buildup of pressure in the gearbox. The pressure is blow-by, (compression getting past the piston rings). Normally only a bit of blow-by occurs. As the bike ages, the rings don't seal up as well due to wear and cylinder expansion deformities. Now the blow-by is becoming a problem. The air/fuel mixture getting past the rings is diluting the oil and actually raising the "oil" level in the gearbox. This puts the oil closer to the vent hose and the increased blow-by pressure carries some of the oil into the air box. What should be done is a fresh bore of the cylinder and new first oversize piston and rings installed. Then do an oil change. Also, have the shop re-seat the valves while the head is off. Now you have a new top end. The bike will perform better now. A less expensive "work-around" is to just change the oil more frequently to maintain proper oil level.

May 16, 2011 | 2003 Honda Xr 250

1 Answer

1988fxstc. Oil is blowing out of what looks like a oil tank vent hose that ends down by the rear tire. This is not the drain hose, but looks like a venting hose that is open near the rear tire. Anyone...

Without seeing the bike, I would guess that this is the crankcase vent. Originally, the crankcase vent tube came up from behind the oil pump and went to the backside of the air filter. A lot of owners changed the routing of this hose due to oil being blown into the air filter. They simply remove the metal part of the tube and replaced it with a short open ended hose running back and ending just forward of the rear tire.

As for the oil blowing out of the tube, it depends on how much oil blows out of the tube. If it's just a mist that will sometimes coalese into a droplet, this is about normal. But, if it's a steady drip or flowing oil, this is not right.

If the mist is heavy, this could be caused by excessive blowby on the rings creating high crankcase pressures. The use of synthetic oil should not increase the blowby unless the rings are in poor shape, then it will. The use of synthetic oil seems to aggrevate any minor leak turning it into a much larger leak.

If the oil is coming out in a steady stream or pumping the oil out of the engine, you proabably have sheared a key in the scavenge gears of the oil pump and it's not pumping the oil back into the oil tank.

Now there is a vent hose on the oil tank but it should be routed to a fitting on the crankcase that is located just above and slightly behind the top of the oil pump.

Good Luck

Oct 17, 2010 | Harley Davidson FXST Softail Standard...

1 Answer

Oil blowing out of trans breather tube

hi 81 yamaha i am concerned about the fuel smell coming out with the oil. could be the carbs flooding filling your crankcase with fuel? if not it sounds like you have blow by which would cause your crank case to be slightly pressured. this is caused by worn piston rings. do not plug your crank vent. if you leave your vent open install small filter to stop dirt from entering jim

Mar 21, 2009 | 1981 Yamaha XJ 650

2 Answers

2001YZ426F oil blowing out vent tube

Dear pmg1, Sat 02-21-2009 5:37pm EST (USA)

RE: 2002 Yamaha YZ 426 F
2001 YZ426F

"Hard to Start if any and/or Oil Blowing Out Vent Tube"

RE: ABOVE is what I'm reading @ the fixya Site @ so.......

Is your Yamaha a 2000 or 2001?
Did You try to start it several times, then it kicked in a little, then a little more, then
started spitting oil and won't even start?
Has it been sitting for quite some time?
Did you put new gas in it?
If so...................................................
Check the OIL and replace if needed..........................................
Put in a can of high test GAS...Spend at least $10.00!.................
Spray a lot of Starter Fluid ($3) into the Air Intake........................
Crank Engine!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !

When you get it running, IF IT'S STILL BLOWING OIL .............................
Add a can of CRANKCASE SEAL'S LEAKS (less than $10) for conditioning
the seals............................................and......................................................



Feb 21, 2009 | 2002 Yamaha YZ 426 F

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