1999 YZ 250 power valve problem?

[nick novice]

i've only ridden this bike twice. the first time it ran like a champ. as it sat in my garage the breather tube off of the cylinder(power valve?) dripped a tar like oil. i went riding saturday. it started up as usual , then died shortly after takeoff. i pulled the plug and it was covered in oil. i cleaned the plug and pulled the power valve breather cover off and cleaned all of the goo out as possible. finally got it started. it blew out a bunch of smoke and then ran like a champ. later, i loaded it up a climb and it did the same thing. i have yet to find a manual for this bike. can somebody help me? is there a seal that is bad or what? i'm going to start pulling it apart today. but i was hoping someone could clue me in as to the problem. the guy i bought this bike from did zero maintenance. since i bought it i've done quite a bit. but i didn't want to dig into the engine until i get a manual. but until then, i hope you cats can help me. thanks.

[ossagp]

I think the problem is not in the valve you are talking about. That hose just lets the accumulated oily residue have somewhere to go. You have the residue because your bike is not running as cleanly as it should.

Start with a clean air filter, fresh sparkplug, and go to the how to section on setting the float in the carburetor (a member named Faded, wrote a good tutorial on that with great pictures). Do the last one first if you want to go in order of priorities and not ease. Float's need setting more often than most realize. The guys you see winning on TV have it before each event if not between heats and motos.

From there you can go onto jetting and replacement of rings, piston, cylinder if necessary. But my money is actually on the FLOATS.

[nick novice]

i hear what you are saying. but it still doesn't cure my power valve problem. i took the covers off. the pistons are too gummed up to move freely. i doubt it's ever been cleaned. can i thoroughly clean it without disassembling it? i guess they're getting stuck in the open position. when we were on the trail, we poured straight gas on the valves to get them cleaned out enough to move freely. i will check the float height to make sure it's at spec. thanks.

[MotoMan]

If I were you I would take the time to dissasemble the valve and completly clean it. If you need a manual check on e-bay they normaly have manuals for most bikes there.

I owned a 99 250 for 3 1/2 years and cleaned the valve a few times, it looks complicated, but in all reality it isn't that bad, just take your time, lay out the parts in the order they came off and you will be fine.

[ossagp]

go with what motoman suggests. you didnt mention that your valves were not moving (from what you are saying i am not sure that they are stuck, as they wont move very well with the linkage connected. but if you are running the engine and going from idle to full throttle etc and they are not moving then they do need cleaning,,badly. usually the ones that are dripping move quite freely though, if the linkage is disconnected).

any rate,,,stuck in any position they are not apt to cause your plugs to turn black or foul. for high hp applications the power valve is routinely eleminated.

[nick novice]

ossagp,
i should have said that the plug gets oil fouled black as tar. the valves do move. but are really sticky. i've been looking for a manual. what years can i use? i see them for a '98 quite often. thanks dudes.

[MotoMan]

If memory serves me correctly the 99 had a new powervalve assembly that in no way was familiar to the 98...but I could be mistaken.

[ossagp]

As I recall the 99 was the first year of the longer stroke engine,,lots must have changed,,,go to yamahaoftroy.com and use the OE parts finder to get the exploded view of the valve and print it out. that alone should help you through that.

[MotoMan]

Originally Posted by ossagp

As I recall the 99 was the first year of the longer stroke engine,,lots must have changed,,,go to yamahaoftroy.com and use the OE parts finder to get the exploded view of the valve and print it out. that alone should help you through that.

Good idea....never thought about doing that one Andy.

[nick novice]

word up. i'll do that.