Black oil dripping from pipe...why?


Sep 16, 2009
Just bought a 2001 yz 250, they guy said he has been working on it through the sumner replacing, piston and re-sleeved cylindper, new crank bearings and seals, new con rod and new clutch, with reciepts to prove it. I took it for a 2 minute blast earlier, stopped it and put it in the shed, i noticed black oil dripping from a black pipe on the left side of the cylinder, it is fixed to the cylinder by 2 screws. What is the purpose of this pipe, and is it normal/ok for it to drip black oil?


May 3, 2002
Since the bike is not oil injected, you jet the bike with the oil mixture and jets for WOT so it does not seize.

So how do you solve it? Ride the bike WOT all the time. Now a lot of time the bikes are jetted either rich or lean. Mostly rich on the 2 strokes. so you can play with the pilot jet see if you can drop a size or 2. Same with the main. If you dont ride sand a lot, you can run a leaner oil mixture like 40 or 50:1, but you will have to rejet from the 32:1 it is setup at from the factory. (ie leaner jets).

The pipe you are refering to is the power valve cover vent. Once the power valves are full of excess oil, it will drip out that tube. Remove the cover and clean the oil up.


Apr 10, 2009
It only does it when i start it and run it only for a few minutes when i do this their is a puddle of oil about the size of a dime on the garage floor. When i run it for hours their is not a puddle at all.


Apr 18, 2006
The oil is from the oil/gas mix that two strokes require. The fact that it didn't burn completely in the cylinder is an indication that the combustion temperature is too low, which could be because it is jetted too rich or perhaps because you simply aren't riding it hard enough. If it runs good, your happy with the performance and it isn't fouling plugs then you can just accept the fact that there will be oil dripping from various spots, usually out the pipe.

There should be a seal (probably just an O-ring) that keeps the exhaust and burnt oil from seeping out the shafts of the power valve. The fact that oil leaks out there indicates that the seals are bad. Next time you are tearing into that area I would plan on replacing the seals but otherwise I would just let it leak.



Sep 16, 2009
Bluesmoke250, does your bike smoke alot? As i stated in the first thread the guy i bought it from claimed he replaced the crank bearings and seals, but ive only started the bike and not run it on a track yet, it was smoking alot when i started it for 5 mins yesterday, it would clear and then smoke a little, i cant help thinking it could be crank seals, even though they have been done? Or it could just be running rich as i got a black drip/line running out of the silencer. I havnt got a manual,do you know what the standard jetting is for this bike? I got a NGKB8ES plug, main jet 180S, needle N3C1 with clhp position second from top, dhdnt take pilot jet out so dont know that one, does that jetting sound standard?


Sponsoring Member
N. Texas SP
Nov 25, 1999
Matt90GT, please learn to jet and quit giving bad advice. Changing your premix ratio is NOT the way to jet! Use the manufacturer recommended ration for fuel/oil mix. Jetting is adjustment to the fuel mix to air ratio.

2 strokes smoke, period. How much they smoke depends on your jetting and to some extent the type of mix oil that you use. At the top of this forum is a jetting link. If your bike runs good, ride it. If you notice particular problems at certain throttle setting or your fouling plugs, go thru the jetting guide and sort out the problem. That small drip from your discription is coming from the vent on the power valve. I wouldn't worry too much.

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