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99' yz 250

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Hello all,

 

I just picked up a yz 250 a couple weeks ago for 1100 bucks and im still not sure if it was a good deal or not. The bike is in overall good condition other than its going to need the back shock replaced which i was figured was 200 bucks most. The previous owner is an old friend and he traded it at an auction from a guy that was pretty wealthy and old, so we both figured it was in great shape engine wise. Of course there is a decent amount of rust on the underside of frame, but not much else where. 

 

Sorry for the short story.. but either way i rode it before i bought it and boy did it have some balls. It kicked over first kick and everything but my only concern was that after it warmed up, when you would stop or pull in the clutch some times to stop it would idle erratic and kind of high and not normal sounding. now we both figured it was just an old gas mix or just a wrong mix so i ended up buying it. I replaced gas with 93 octane pump and mixed 32:1 with yamalube, checked coolant good, and checked trans oil and looked pretty cleanicon1.png... i then proceeded to take it down to woods at my house and it was running good and great but after a while it started doing that high idle shit again so i was messing with air screw figuring maybe it was too lean so i turned it in which seemed to help but not that much it still had an odd sounding and high idle? i then took it home and took apart carb hoping it was just dirty or had plugged jet but it looked spot clean? then the day after it i started it and it stalled on me then would not start again? i'm thinking i possible got some water in the carb somehow so i drained carb took out plug and let her dry out while kicking it a few times with plug out. it then fired up the next day but still high idle!? also after riding the bike it leaves a spooge pile of light gray oil from pv overflow, which makes it sound like a rich condition? but the high idle sounds like a lean condition? 

 

Sorry for saying so much but i just wanted to be as descriptive as possible so if someone can help me out all the details are there. i also am just wondering if this is a more serious problem or is it something i am overlooking? i cleaned the carb and it seemed really clean already the only place with some dirt was in the choke area which is because the choke valve also controls idle and was loose which is possibly where i think i may have taken in water? if i am wrong in any aspect please someone correct me. i am open to any suggestions considering i am fairly new to repairs on bikes.

 

Thanks ahead of time if anyone can help me.

 

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Standing a long time could well have affected the crank seals and with those or one of them blown you could have an airleak. 

Spooge is not a rich indicator but rather than engine temps are not high enough, due to riding style?

 

First thing to do on a used bike would be to check the piston, cylinder, crank IMO better safe than sorry.

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Standing a long time could well have affected the crank seals and with those or one of them blown you could have an airleak.

Spooge is not a rich indicator but rather than engine temps are not high enough, due to riding style?

First thing to do on a used bike would be to check the piston, cylinder, crank IMO better safe than sorry.

I second that check all seals and bearings... I didn't and $400.00 later I have new crank seals... Save some cash and check it out thoroughly now.

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Don't worry about spooge till you get the high idle fixed.

 

Does the idle increase when you turn left and right?

Do you have freeplay in the cable or is it overadjusted at the right grip?

 

Have you tried turning the carburettor idle adjuster in?

 

Search for links to free service manuals on TT YZ 2-stroke home if you're not sure on which adjuster this is and/or how to adjust your airscrew.

Edited by Swappa

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i was told that the bike did sit for a decent while.. that's why i was surprised it fired up first kick? but i did allot of research trying to figure out a high idle and it all led me to air leak or running lean, and i also read about crank seals leaking which kind of scares me. i sprayed starting fluid in small increments while waiting between sprays pretty much everywhere, even the ignition side cover and clutch side cover if that is correct? and no idle changed at all. now correct me if i'm wrong but if the crank seals where leaking but the cover gaskets weren't would that not let any extra air in or not? if i'm wrong what is the correct way to check for crank seal leaks and what is the extend of replacing them? 

 

Also responding directly to arnego2 and breakneckyz. how do i go about checking piston cylinder and crank? with spark plug out , carb* out and exhaust out i tryed to watch cylinder movement and it seemed fine but that doesn't really say much. but i also looked at ring from exhaust side and looked fine. I also looked at top end of cylinder from spark plug hole with lights and such and it seemed alright other than some burnt oil/hopefully not rust crud on top of cylinder..

 

but directly towards breakneckyz, if the seals are shot what is the point of knowing ahead of time? im going to have to replace them anyway which in my mind wouldn't save me any money. other than if your saying replace them before it causes more problems.

 

Either way thank you all for the responses .. i wish i had a father figure or someone else to help me with this, so your help is much appreciated.

 

 

Edit* sorry i didn't respond to your questions swappa. I haven't fully checked, but from ridding the bike and trouble shooting it does not seem that idle changes when i move handle bars side to side and when i first picked up bike there was absolutely no free play in the throttle so i loosened the adjuster nut right by throttle to increase free play.  especially considering a yz 250 has allot of power i wanted to tame it as much as possible and avoid whiskey throttling . But from what i have messed with it does not seem like there is anything to binding or catching in the throttle cable. it will increase idle when i pull in the clutch going down a hill completely straight or just even warming the bike up sitting in yard.. and someone did tell me to just turn the idle down, which from my experimenting is turning the choke knob counter clockwise and it does in fact lower the idle but it still sounds not normal and quick. i cant really explain idle the not normal and quick in words so maybe this weekend after i work my 60 hour a week :( , lol i will try and take a video. 

Edited by Banger92

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on my 250.. the bearings had corrosion on the races (from sitting) and the seals were shot. I just dropped $400 to replate my cylinder, new piston, gaskets, replace the crank bearings/seals, and other rebuild expenses.

 

If I would have caught it in time.. it would have been significantly less. The clutch side (Wet side) crank seal cannot be checked with starting fluid. Quite honestly, I don't know how you can relaibly check the crank seals with the starting fluid method IMO.

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oh wow ok i see. did that cost include labor also? and what were the symptoms you were having? the only problem with my bike is it doesnt idle right. it rides fine and pulls fine.

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remove your choke and clean it, make sure it isnt sticking.  You might dirt or something holding the choke open causing the idle once warm.  Hopefully thats it...

 

buying a used dirt bike is always risky.  You have to rely a lot on the seller.  Buying one third party that sat you pretty much have to plan on tearing it down and rebuilding it.  Hopefully not but that's my train of thought.  Its 14 years old and regardless of how much it was ridden, sitting is probably worse.  Hopefully not, but whenever you look at an old bike, before you try to start it(you can kick it a bit holding in the kill switch to make sure the motor is free) you want to drain the gas, oil and coolant and replace. 

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oh wow ok i see. did that cost include labor also? and what were the symptoms you were having? the only problem with my bike is it doesnt idle right. it rides fine and pulls fine.

This is with me doing all the work.. Splitting cases is educational lol

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i'm pretty sure the choke is free because when i start the bike with the choke on if i don't turn it off in a like 20 seconds the bike wants to die? i'm not sure what that means but i'm guessing the bike did sit for a while but it was an older guy who barley rode the bike. i drained all the old gas but never changed coolant or trans oil because they both looked clean? could that be causing problems or already have? lol. and also when i replace trans fluid the manual says use 10w-30 but alot of people were telling me that the fluid they use is red? actual trans fluid or what?? and to breakneckyz you had to split the case to replace the crank seals? or was that just because you needed to replace bearings also and gaskets?

 

but thanks for all the help guys

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Banger,

In case its not clear from the previous posts, if your crank seals are leaking, there will be fresh air leaking into the motor while its running. This screws up the air:fuel ratio. Your caburtettor is finely tuned to make this mix for you. Your crank seals may be old/hardened leading to an air leak and a lean condition. Too much air (=lean) will burn up your motor in short order which is why I suggested you make this a priority to fix over all else. The consequences can be great and expensive ... as breakneck has described.

Now, crankseals are not quick or easy to replace (but much quicker than replacing the top half of the motor plus crank).

On your way to figuring out if you have an airleak from hardened crank seals, you need to figure out what is causing your high idle and if its related to a lean condition and/or an air leak.

 

Your high idle might be caused by:

-idle turned up too high @ carburettor, or

-throttle cable too tight, or

-choke sticking, or

-other (need more suggestions from TT), or

-lean condition cause by:

            - airleak crank seals left or right

            - airleak @ base gasket (between cylinder and engine block)

            - other (need more suggestions from TT)

I can't think of any other external factors that you might want to check and I can't think of anything else that might be causing a lean condition. I'm really just tryign to help you with figuring out priorities and checks to make before your arrive at cranks seals being the problem, because crank seals are not simplest things to replace and I hate jumping to conclusions >> deadend. Given that you have sprayed starter fluid at the left seal and it didn't cause a variation in the idle, this would lead me to think that at least the left hand side is still good (assuming you did this check correctly).

My best advice would be to post a sound sound byte of your bike, a picture of your spark plug, and a list of the numbers on your jets and needle.

Also, visit your friendly Yamaha dealer ... you should be able to ask one of the service techs to listen to it run and they could most likely help you with the diagnosis for free.

Edited by Swappa

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ok sorry im just thinking way to much and trying to figure it out but i work so much i dont have alot of time. I did infact spray starting fluid on clutch side and nothing happened so that must mean its not leaking there.

 

But now after more diagnosing, what i am even more confused with is that my plug shows signs of running rich and i must of actually fouled one the other day.. bike would not start back up at all and bogd every time i tried to get on it until it came to a stall. Also i am getting some thick spooge from the pv breather hose, especially after turning bike off and putting away.

 

So basically i am lost, i tried thinking of everything possible and trying different things. and now the fact that im fouling spark plugs and the bike will not run with choke makes me think its running rich? but wth do i know at this point..  i will post a picture of the spark plug tomorrow and as far as jetting i have a 50 pilot and 172 main. which from what i have read is stock? i will have to check the needle and clip position also and repost.

 

 

Also back to high idle, its more of a like rough idle not so much high as i described it. or it at least has gotten alot lower somehow, because when i first got it it would idle high like when you would pull in clutch coasting in a gear it would raise. it just doesnt idle like a normal 2 stroke to me. i will try and take a video with the best sound i can get. i will also look into taking it to my local yamaha dealer.

 

Also to respond to maniac i have seen the thread on that homemade leakdown tester and i was thinking about purchasing the materials this weekend and trying to build it. i figure it cant hurt and can always be used in the future.

 

Thanks again for all the help guys and sorry swappa if i ignore/missed some stuff that was already told to me. im just having trouble

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ok so i havent had time to take a video yet but i did have time to start it up for a little. it wont even stay running without giving it some throttle? and like i said before it will not run unless you turn choke off withing 10 seconds. is that just mean its really rich on low speed circuit or something engine wise? i tried messing with the air screw figuring if it was rich to turn it out but it didnt help at all. i actually fouled a plug trying to keep it running and it is also splooging alot of spooge out pv breather after i shut it off it has a silverish color to it and is thick. could that be right side crank seal? only thing is it isnt smoking much so that wouldnt make sense.

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anyone? i even compression tested it the other day and im getting well over 200psi. im hoping tommorow i will be able to take a video if that helps. ive also heard alot of people say race gas cures stupid problems like this but really?

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anyone? i even compression tested it the other day and im getting well over 200psi. im hoping tommorow i will be able to take a video if that helps. ive also heard alot of people say race gas cures stupid problems like this but really?

A video would really help out with this. I'm not sure if it was mentioned before, but have you checked your reeds for cracks/chips/wear?

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ok so i havent had time to take a video yet but i did have time to start it up for a little. it wont even stay running without giving it some throttle? and like i said before it will not run unless you turn choke off withing 10 seconds. is that just mean its really rich on low speed circuit or something engine wise? i tried messing with the air screw figuring if it was rich to turn it out but it didnt help at all. i actually fouled a plug trying to keep it running and it is also splooging alot of spooge out pv breather after i shut it off it has a silverish color to it and is thick. could that be right side crank seal? only thing is it isnt smoking much so that wouldnt make sense.

10 seconds for YZ with choke is pretty normal. Minimal use of the choke is best, to avoid fowling a plug. Any hope of getting a yz250 to purr at idle on choke while cold is a bit ambitious. It will only be possible when at operating temperature.

 

That's not to say you need to take off in the first 30 seconds after firing it up to avoid fowling a plug. Start on choke, run for a few seconds, turn off choke shortly afterward, try and keep it running without the choke till you can start to feel some warmth in the radiator, and then you start out at a moderate pace.

 

Airscrew is a relatively fine art and takes a keen ear to determine the optimum setting/best idle. It starts with engine at operating temp, no choke, and a steady hand at 1/8th throttle or turn idle to where it will hold its own steady.

 

Spooge and fouling plugs is pretty common if you bike is still cold and/or has a lot of old mixture set in the engine from not having a run or recent cold start.

 

Oil leaking from the PV overflow and a little from the silencer end or joint is not a huge problem ... can be fixed later. Check your calculations .. you should be mixing 155 mls oil to 5 liters of gas for 32:1. In lamens terms, that's 8 fluid ounces of oil to 2 gallons of gas. You can go as lean as 5 ounces of oil, and not risk seizure, but anywhere between 8 and 5 ounces to 2 gallons is unlikely to change spooge ... as said before, that's rich jetting for your skill, altitude, and terrain.

 

Post a video or sound byte, please.

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ok i will do those exact starting steps you have said. and i use a ratio right cup. i did mention in this video im posting i was mixing 32:1 but now im going to try 40:1. i was also using yamalube 2-r now i have klotz which is synthetic oil. in the video i missed to also show/explain that my compression is well over 200. well here is it.. after i post this im going to go down and start the bike ans take another video

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having trouble uploading video.. guess its too big? its like 6 min, so i just put it on youtube

 

 
EDIT* nevermind.. youtube isnt working and you cant upload files bigger than 8mb on here. any suggestions?? 
Edited by Banger92

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99 for 1100 isn't bad. I got my 98 for 1050 so. Mine was in pretty much the same condition, but my plastics were a bit scratched up. After putting about $700 into mine I'm happy.  :thumbsup:

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