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grrr another prob.

By superbob,
in WR250F/YZ250F/YZ250FX

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superbob

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i just installed my 290 kit and iron man sprockets for higher top end and i am very excited. but... yet another problem has come up. this morning before i was supposed to go riding, i decided to check my coolant level. (engine ice) and noticed it was a bit low. hm. so i filled it up...no bigie right? well i started to think about what could have caused it to go down. i just installed a new piston and cylinder, and rode gently to ensure proper break in. so maybe one of the gaskets wasn't on right? i decided to start it up to check for any external leaks...none. my problem started when i stopped the motor and let it cool so i could check the coolant level again. when i looked in the radiator, i could see debris in the coolant. i checked the cap and rubbed off little black specks of what looked like gasket, but im not sure. i started it up again, and noticed that my leak was coming from the breather hose as if it was over heating. the coolant is not discolored or anything and i cant figure out what is causing it to do this. also, there is no evidence of water in the oil.

any thoughts as to where to start would be greatly appreciated

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intensem1rider

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You most likely have air in the system. What I do it fill the rad up to the top, put the cap on then slowly lay the bike down to the left right down to the handle bars, then to the right, then check it, it should have gone down. If its being really stubborn you can do that with the bike running. Then after all that your coolant should never go down again, if it does, then you must have a problem.

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ButchWR250F

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i just installed my 290 kit and iron man sprockets for higher top end and i am very excited. but... yet another problem has come up. this morning before i was supposed to go riding, i decided to check my coolant level. (engine ice) and noticed it was a bit low. hm. so i filled it up...no bigie right? well i started to think about what could have caused it to go down. i just installed a new piston and cylinder, and rode gently to ensure proper break in. so maybe one of the gaskets wasn't on right? i decided to start it up to check for any external leaks...none. my problem started when i stopped the motor and let it cool so i could check the coolant level again. when i looked in the radiator, i could see debris in the coolant. i checked the cap and rubbed off little black specks of what looked like gasket, but im not sure. i started it up again, and noticed that my leak was coming from the breather hose as if it was over heating. the coolant is not discolored or anything and i cant figure out what is causing it to do this. also, there is no evidence of water in the oil.

any thoughts as to where to start would be greatly appreciated

When you put the head gasket on did you use Copper Coat on it (or some other kind of gasket sealant)? The stock Yamaha head gaskets have a coating built into them (the black stuff that sticks to the cyl/head when you take the head off). This stuff makes it so you can just slap a Yamaha gasket on & tighten it up. I used a moose gasket kit not too long ago & promptly blew the head gasket (on the first fire up, idling). Took the head off, had water on top of the piston. Used a Yamaha head gasket, sealed perfectly.

I've heard that when you put an Athena 290 kit in you need to use gasket sealant. So when I installed the first one of those, it got a healthy coat of Copper Coat. And it didn't leak.

If the engine isn't hot, but it's pushing coolant out the overflow, the pressure is coming from combustion, and going thru the head gasket to the water jacket. You can also smell the coolant. If it's been leaking combustion into it, it'll smell like the tailpipe does.

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superbob

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think maybe its my radiator cap? when i rotate the spring and seal assembly on the cap, there is a slight grinding noise...bad cap? the black specs resemble the material of the cap seals...

just throwing out thoughs here, i need this ready before next weekend. my buddie has a four fitty and ive just told him that id out drag him at reiter on sunday, so i cant have this thing over heat on me. i know ive got the power to weight ratio on him and gearing, i should be fine. my bike weighs in at 192lbs and im only 165. he's a pretty big kid and on a 450crf (stock)

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Dexter643

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think maybe its my radiator cap? when i rotate the spring and seal assembly on the cap, there is a slight grinding noise...bad cap? the black specs resemble the material of the cap seals...

just throwing out thoughs here, i need this ready before next weekend. my buddie has a four fitty and ive just told him that id out drag him at reiter on sunday, so i cant have this thing over heat on me. i know ive got the power to weight ratio on him and gearing, i should be fine. my bike weighs in at 192lbs and im only 165. he's a pretty big kid and on a 450crf (stock)

How'd you get it down to 192lbs.?

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ButchWR250F

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no, i did not use any type of gasket sealent on the head gasket, it was a triple, or double layer cometic gasket set. said nothing about any type of sealent, but was sort of beveled,

That could explain the black stuff in the coolant. When you scraped the black sealant off the cylinder pieces of it could have fallen into the water jackets.

I forget how many cylinder heads I've installed, and I've never had one blow as fast as the moose one I did 2 weeks ago. I learned my lesson, I'll use gasket sealant on all of them (except for stock Yamaha).

Did the coolant smell like combusion? It should if it's been leaking. The motor I did I started it once & let it idle until the radiator got hot, then I shut it off.

I went back to try & start it & I kicked it until my leg fell off (JK) & no start.

I removed the exhaust pipe & it was wet with water!!! So that dang thing blew in 3 minutes with no load on it. So I think it may be worthy of a little time on your part to check that out. Hopefully it's not that, but it very well could be.

Good Luck!!!!

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superbob

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i'll see if it smells like combustion before i tear into it, i think it is just peices of the old one. i'll drain and flush it...prob persists, tear down, if not, i'll ride it. problem solved. as for the weight. little things add up. chain guids all either carbon fiber or ti. rad guards: ti, skid plate: ti, sub frame, wheels, air box, for some reason my suspension is lighter than stock. cylinder is lighter. exhaust is lighter. bars, flywheel, the list goes on. there are alot of things ive done to it not listed in my garage, but according to the scales, it weighs in at 194.8 lbs w/ quarter tank, oil, and coolant.

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superbob

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even if i do need sealent on the head gasket, which i still doubt, that doesnt explain why the coolent is escaping out of the breather hose. if that were the case, it would evaporate and comeout the exhaust or out of the head gasket. instead, it just flows right out of the breather hose, which is why i am leaning toward it being a rad. cap problem. i'll ask yamaha

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drjack

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If the engine isn't hot, but it's pushing coolant out the overflow, the pressure is coming from combustion, and going thru the head gasket to the water jacket...

That explains it. What part of the gasket is blown determines where the pressure and or fluid goes.

But since you think it's the rad cap, the cheapest and easiest thing to do would be to borrow (or even buy it you have to) another rad cap and try it.

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MX813

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i'll see if it smells like combustion before i tear into it, i think it is just peices of the old one. i'll drain and flush it...prob persists, tear down, if not, i'll ride it. problem solved. as for the weight. little things add up. chain guids all either carbon fiber or ti. rad guards: ti, skid plate: ti, sub frame, wheels, air box, for some reason my suspension is lighter than stock. cylinder is lighter. exhaust is lighter. bars, flywheel, the list goes on. there are alot of things ive done to it not listed in my garage, but according to the scales, it weighs in at 194.8 lbs w/ quarter tank, oil, and coolant.

And you ride this at Reiter? My 04 250F weighs in at 225 or so with skid plate, 3.2 gal tank, heavy duty tubes, etc....so I can ride at Reiter without breaking down.

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