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YZ250F 02. Radiator low & wont start.

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Greetings,

 

We have just picked up this YZ250F 02 model and had about a day and a half riding it when it stopped running. The previous owner had it sitting for about 2 years but assured me of its mechanical integrity. I quizzed him again about a month after the sale of the bike & asked if I needed to know anything about the bike and again he assured me it was all good.

 

So, since getting it I have changed the oil & filter, fresh fuel in it and it ran very nice...until it stopped running. 

 

Upon inspection I have found that the radiator is dry from opening the cap and there is moisture in and around the spark plug but no signs of a weep from the weep hole. I intend to top up the radiator & see how much fluid it takes and will then know how much it has lost. I do have spark.

 

The motor is not seized & pretty sure it didnt get hot, cook itself & die. Not knowing the layout of the head on these bikes, could the water in around the spark plug be from wash down or is it possible for the head water jacket to have let go around the plug, if there are any jackets around there?

 

So my questions are:

 

Where do these bikes typically lose coolant from?

Are there any water cooling jackets in the head around the spark plug hole?

Do these bikes use coolant?? Unlikely I would think especially considering it was a cool day.

I'm suspecting a carb issue as well as it doesn't idle well at all, dont know the Keihin carbs too well so where would I start apart from the obvious drop the bowl of & blow through the jets etc.?

 

Appreciate any feedback as I'm new to the Yamaha's. My son & his step bro now have a WRF250 & YZF250 so I expect to be frequenting here quite a bit now :)

 

 

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sitting for about 2 years

>Not great.... but OK.

 

it stopped running

> Uh Oh

 

the radiator is dry from opening the cap

>Never good

 

moisture in and around the spark plug but no signs of a weep from the weep hole.

>Probably from washing.  The weep hole will sometimes fill with dirt.  Its supposed to let water and dirt out before you remove the sparkplug.  You pull the cap, blow compressed air down in there and clear the hole so junk will flow out and not go into the engine.

 

I do have spark.

The motor is not seized

>Good

 

Where do these bikes typically lose coolant from?

>Head gasket

 

Are there any water cooling jackets in the head around the spark plug hole?

>Water does flow into the head.  The head gasket has passages in it, and that's probably when the problem is... needs headgasket replaced.

Use Yamaha replacement.

 

Do these bikes use coolant??

>NO.  The only reason they will loose coolant is if you let them sit and idle and get hot.  That will cause overheating and dump out the overflow.  The WR has a catch tank, but the YZ does not and it goes on the ground.

 

Unlikely I would think especially considering it was a coolicon1.png day.

>Not too sure about that... don't let it sit and idle.

 

I'm suspecting a carb issue as well as it doesn't idle well at all, dont know the Keihin carbs too well so where would I start apart from the obvious drop the bowl of & blow through the jets etc.?

 

> There are reems of posts on carb issues.

I'd do a thorough clean out from the tank down, clean out the petcock, replace the fuel line, check float and float level, and float valve operation.

Note jetting, pilot, main, leak... write the numbers down.

Fuel screw, screw it in until it gently bottoms out counting the turns are you go and record that number.  Then remove it and clean the needle and passages.

Some people say replace the pilot jet.  I've had good luck cleaning them out, but I have tools for that.

Check accelerator pump for operation.

 

Before a ride, I check coolant in the YZs and check the resovoir level in the WRs.

Good luck with it.

Ron

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Thanks Ron.

If Im doing a head gasket I will probably be looking at the piston & rings while I'm there. What else do you look at whilst inside??

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Well, I just did a top end on son's '02, but it wasn't starting and I knew the valves were closing up and we'd never done a top end.  When I opened it up, it was the best of everything I'd hoped for.  The rod was tight on the crank and the piston pin were tight.  You need to check those and possibly mic them.  My '03 bike had knock and it turned out to be a worn rod small end AND the piston pin hole in the piston... "who would a thunk it."  I put in a Hot Rods crank and oem piston... quiet as a mouse now, except for the Dr D on the end.

 

Spray brake cleaner into the intake and check for leaking out thru the valve seats, then do same for exhaust.

Also check the size of the shims.  Anything small like a 1.20 or 1.25  or leaking valves might indicate that its due for valve replacement.

NOTE:  There will be some weaping, but it should hold fluid. 

 

Hold open the valves by hand and look at the mating surfaces.  If the valves are "tuliped", I might go ahead and replace valves..... ESPECIALLY if I intended to keep the bike for a while.

 

Check the small cam sprocket on the crank; sharp pointed teeth are worn out and crank replacement is only choice.  Also a check on this is take the cam chain and drop it on the table.  Then pick it up by one link and see if chain links kink up and doesn't straighten out on its own when you pick it up.  For $25, its cheap insurance.

 

Pull the right side cover, check the clutch basket for notches worn in the tangs from clutch plates.  You can file them flat if its just starting to happen to them, but otherwise replace the basket.  While the clutch is out, remove the oil pump and inspect the gearrotor for scoring.  There's a spec for clearance in the book.   Replace if necessary.

 

Go back clean.  Use brake cleaner and clean shop rags.  Give yourself twice as much time as you think you need to do it, and stop often, check work, rest, and for goodness sakes stop if you get tired, or start rushing the job to make a deadline or something. 

Mistakes are easy to make and hard to fix. 

If you don't have time to do it right, when will you have both time and money to re-do right?

 

Ask questions.  There's a lot of "experts" on here and no shortage of opinions and advice....lol.

Good luck, L8tr, Ron

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Hmm,

Might need more than just that head gasket then :)

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Update:

Tore the motor down & took the cylinder into work to ask one of the mechanics his opinion.

Not perfect but will get "at least another 30 hrs out of it".

Couldn't get the feeler gauge in the gap, I had 3 x 1.7mm shims and 2 x1.8mm shims. Took a punt and went to 1.55mm shims. I now have 1 gap I can measure and 2 that I still cannot get the feeler gauges under. Ordered the hot cams shim kit and now waiting for it to arrive.

Did a leak test by spraying carb cleaner into the ports when the head was off, all 5 valves held fluid so not fearing the worst...yet.

Bike now fires but dies straight up. Seems to lack compression & not need the decomp lever, most probably due to valve clearance...or maybe I'm just used to kick starting a 650r :)

Plan of attack:

Shim the valves, get a clearance then see how it goes. Planning the rebuild for the summer months in Oz when it's too hot & dusty to ride.

Thoughts???

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Update:

Tore the motor down & took the cylinder into work to ask one of the mechanics his opinion.

Not perfect but will get "at least another 30 hrs out of it".

Couldn't get the feeler gauge in the gap, I had 3 x 1.7mm shims and 2 x1.8mm shims. Took a punt and went to 1.55mm shims. I now have 1 gap I can measure and 2 that I still cannot get the feeler gauges under. Ordered the hot cams shim kit and now waiting for it to arrive.

Did a leak test by spraying carb cleaner into the ports when the head was off, all 5 valves held fluid so not fearing the worst...yet.

Bike now fires but dies straight up. Seems to lack compression & not need the decomp lever, most probably due to valve clearance...or maybe I'm just used to kick starting a 650r :)

Plan of attack:

Shim the valves, get a clearance then see how it goes. Planning the rebuild for the summer months in Oz when it's too hot & dusty to ride.

Thoughts???

Did you pressure test the cooling system and perform a compression test before tear down? I would have done that before a tear down.

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Did you pressure test the cooling system and perform a compression test before tear down? I would have done that before a tear down.

Meh...

Didn't bother on the advise posted up about the head gasket leaking.

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Update:

Tore the motor down & took the cylinder into work to ask one of the mechanics his opinion.

Not perfect but will get "at least another 30 hrs out of it".

Couldn't get the feeler gauge in the gap, I had 3 x 1.7mm shims and 2 x1.8mm shims. Took a punt and went to 1.55mm shims. I now have 1 gap I can measure and 2 that I still cannot get the feeler gauges under. Ordered the hot cams shim kit and now waiting for it to arrive.

Did a leak test by spraying carb cleaner into the ports when the head was off, all 5 valves held fluid so not fearing the worst...yet.

Bike now fires but dies straight up. Seems to lack compression & not need the decomp lever, most probably due to valve clearance...or maybe I'm just used to kick starting a 650r :)

Plan of attack:

Shim the valves, get a clearance then see how it goes. Planning the rebuild for the summer months in Oz when it's too hot & dusty to ride.

Thoughts???

 

The the cam to bucket clearance has closed up...the seats are done.  They will just keep pulling up....  Valve job time...  Shimming of valves in an initial setting...not an ongoing adjustment.  Once they start closing up...they will not stop.

Edited by Blutarsky

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The the cam to bucket clearance has closed up...the seats are done.  They will just keep pulling up....  Valve job time...  Shimming of valves in an initial setting...not an ongoing adjustment.  Once they start closing up...they will not stop.

Bugger :(

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