My YZ250F is acting up! Help!!

[khan]

Hey barfers!!

I've been riding my 2002 YZ250F that I got used about 3 years ago, it has been running pretty good with a lot of compression.
Just recently, 2 weeks ago the kick start suddenly started feeling really soft. I dont have to use the compression release lever anymore because the kick is just too soft. When there was a lot of compression it was really hard to kick start the bike but i would eventually get it to start in about 3-4 kicks, but now after the compression is gone, its easier to kick but the bike just wont start, even after 20-25 kicks.

After checking the spark plug (clean), the fuel line is supplying fuel to the carb, the carb is clean (still cleaned it thoroughly again), radiator is full, no leaks nothing at all. I was confused but then someone at the local MX track suggested bump starting it.. and so for the last few rides ive been bump starting it, it starts right up and i've been riding it however seems like its not pulling hard anymore. Feels like the power isnt there anymore.. out of soft sandy turns the bike bogs sometimes, i cant pull 2nd gear wheelies anymore doesnt matter how hard i dump the clutch, the front just doesnt come up as fast as it did..

Im a complete newbie when it comes to dirt bikes so dont know what to do from here on. what are you thoughts!?! what all do you think i should check and what do you think needs to be replaced.

I apologize for the long post, thanks for baring with me!

Much love,
Khan

 

[Junkie]

my money is on the exhaust valves tightening up and burning

 

[byke]

My guess is that ^^^ caused by never cleaning your air filter.

 

[Junkie]

Even if properly maintained, 250Fs have a fairly finite valve life.

Improper maintenance sure doesn't help though.

 

[khan]

my money is on the exhaust valves tightening up and burning

So i should replace the exhaust valves? while im in there should i replace something else just to make sure?

My guess is that ^^^ caused by never cleaning your air filter.

I do change my air filter every other ride but i do live in a very dusty party of the world.

Even if properly maintained, 250Fs have a fairly finite valve life.

Improper maintenance sure doesn't help though.

any recommendation of what valves i should get??

 

[Junkie]

Start by checking your valve clearances. I bet they're VERY tight.

When you replace the valves, you should probably do the intakes as well. You should have the head cut for the new valves too.

 

[khan]

Start by checking your valve clearances. I bet they're VERY tight.

When you replace the valves, you should probably do the intakes as well. You should have the head cut for the new valves too.

Sure thing, i'll replace the intake and the exhaust valves. :thumbup

What do you mean by "have the head cut for the new valves" ??

 

[Junkie]

The burned valves (and wear over time in general) most likely did some damage to the valve seats. The way to fix that is to have a machine shop re-cut the valve seats.

In some cases you can lap valves, but only if there's minimal damage. Additionally, you can't lap Titanium valves (which I believe you have) as it damages the coating, leaving the very soft metal exposed.

 

[kxmike]

check out http://fastheads.com/

 

[augustiron]

Check valve clearance and adust to spec.
Then perform a leak down test before taking anything apart.

 

[KTMJACK]

I would think the valves are just fine :thumbupIt's not a Honda
Do you have the 02 Cam still and i would check the free play in the decompressor cable make sure it's not stuck Move the lever on the head make sure it's working
I would change to a 03+ Exhaust cam with the Auto decompressor
It will be so much nicer to start

 

[OaklandF4i]

Moin -

You have some good advice on where to start figuring this out. I would STRONGLY suggest you park it until the bike is diagnosed and repaired. You run the risk of potentially further damaging the engine or a very expensive catastrophic engine failure (worst case.)

Augustiron is spot on, adjust valves and do a leak down test to start diagnosing what is wrong with your engine. I dont remember if your YZF still has the manual decompression attached to it still or it has been updated as Jack mentioned. If so, follow his advice. I'd agree with Junkie re the valves if I were to randomly guess. Its the best guess, but again, only a guess without actually tearing into the motor to diagnose.

I assume you and the bike are in Lahore right now. You need to reach out to your local network and find someone you can trust with the experience, tools, and knowledge to work on it properly. These bikes are not like the 100-200cc Indian built bikes (for example the titanium valves as mentioned cant be lapped.) Someone without the skills or knowledge could actually due more damage even if they got the bike running again in the short term.

You have mentioned before how it's harder to acquire bikes like this at home. So it would be a shame to not repair and maintain this right, if the motor actually does fail it can become a throw away bike as the parts to rebuild can be cost prohibitive.

The YZ250F is known as one of the more robust and reliable of the high performance 250F's, but they still wear out and need regular maintenance. Your loss of compression may be a blessing in disguise, it may be telling you it needs attention instead of just a random catastrophic failure. :thumbup.

If the valve adjustment is indeed way out of spec, it cures the compression issue and your leakdown test after comes out positive after adjusting.... you will need to keep a very close eye on the valve adjustment interval (measuring/adjusting on a shorter interval). Often on older high hours bikes, when they (valves) start to move, they continue to move quickly telling you that the motor is at the end of its life cycle and need of a fresh rebuild. If thats the case, its time to open the motor up. Its always cheaper to rebuild than repair a motor failure. Not a scare tactic, just a heads up. :afm199

KXmikes link is great for an economical approach to the head/valve rebuild. If you do open the motor, it would be wise to pull the cylinder and do a full inspection. Two of the three YZ250F motors I have in my garage right now suffered a rod big end bearing failure on the crank. :x

I'm pretty swamped the next four days, but if you want to chat offline next week, we can. And looking forward to your next visit so we can ride again! Hopefully the forests are open by then from all the fire damage. :ride

 

[khan]

Moin -

You have some good advice on where to start figuring this out. I would STRONGLY suggest you park it until the bike is diagnosed and repaired. You run the risk of potentially further damaging the engine or a very expensive catastrophic engine failure (worst case.)

Augustiron is spot on, adjust valves and do a leak down test to start diagnosing what is wrong with your engine. I dont remember if your YZF still has the manual decompression attached to it still or it has been updated as Jack mentioned. If so, follow his advice. I'd agree with Junkie re the valves if I were to randomly guess. Its the best guess, but again, only a guess without actually tearing into the motor to diagnose.

I assume you and the bike are in Lahore right now. You need to reach out to your local network and find someone you can trust with the experience, tools, and knowledge to work on it properly. These bikes are not like the 100-200cc Indian built bikes (for example the titanium valves as mentioned cant be lapped.) Someone without the skills or knowledge could actually due more damage even if they got the bike running again in the short term.

You have mentioned before how it's harder to acquire bikes like this at home. So it would be a shame to not repair and maintain this right, if the motor actually does fail it can become a throw away bike as the parts to rebuild can be cost prohibitive.

The YZ250F is known as one of the more robust and reliable of the high performance 250F's, but they still wear out and need regular maintenance. Your loss of compression may be a blessing in disguise, it may be telling you it needs attention instead of just a random catastrophic failure. :thumbup.

If the valve adjustment is indeed way out of spec, it cures the compression issue and your leakdown test after comes out positive after adjusting.... you will need to keep a very close eye on the valve adjustment interval (measuring/adjusting on a shorter interval). Often on older high hours bikes, when they (valves) start to move, they continue to move quickly telling you that the motor is at the end of its life cycle and need of a fresh rebuild. If thats the case, its time to open the motor up. Its always cheaper to rebuild than repair a motor failure. Not a scare tactic, just a heads up. :afm199

KXmikes link is great for an economical approach to the head/valve rebuild. If you do open the motor, it would be wise to pull the cylinder and do a full inspection. Two of the three YZ250F motors I have in my garage right now suffered a rod big end bearing failure on the crank. :x

I'm pretty swamped the next four days, but if you want to chat offline next week, we can. And looking forward to your next visit so we can ride again! Hopefully the forests are open by then from all the fire damage. :ride

Hey Oakland!! That was a lot of help.
Update with the bike!
A mechanic friend of mine and I adjusted the valves, cleaned out the carb (which was already pretty clean), changed the oil and the filters and the bike fired up on the first kick.

I took it to my MX track and the bike performed perfectly the entire day. ive changed the air filter since but havnt gotten the chance to ride it again.

Now i have the topend rebuild kit, the piston and gaskets. I ordered it a month ago from bikebandit.com and a friend brought it to pakistan from the states for me..

I'm thinking i should not just do the top end piston kit but also the valves and 03+ Exhaust cam with the Auto decompressor.

Can someone here help me find the correct valves and exhaust cam with auto decomp for my 2002 Yz250f.. ive searched up google for a couple of hours now and with so many options its just confusing..

 

[Junkie]

how tight were the valves? once they go a certain distance that's a sign that they're on a downward slope.

 

[augustiron]

Keep records of the before and after measurements of the valves, always.
Keep records of compression test and leak down numbers if performed.
Put an hour meter on the bike and do regular maintenance based on actual hours, not guesses.

Congrats on getting it running great and enjoying it why would you tear it apart now?
Put the rebuild kit on the shelf for when it is really needed and enjoy the bike.

 

[OaklandF4i]

Moin -

Any 03 04 05 exhaust cam should work (it comes with the autodecompression on it, not seperate.) 06 -08 might even work. Ask same question on thumpertalk.com to clarify Even ebay if it looks good, ie no wear or discoloration on the cam lobes. RockyMountainATV tends to be a bit cheaper than Bikebandit FYI. OEM valves for your year of bike. Nothing changes with the new cam.

A few things. Now that it is running, you really need to do a leak down test on the motor. That or a compression test is going to tell you if need to do top end on it or not. If you dont know or think its around 200, I would rebuild the top end and then keep track of hours.

And as already mentioned, write down how much your valves moved. I assume it was your exhaust valves. Check them again in 15 or 20 hours to make sure they arent moving again... this is important. Dont wait until you dont have compression again or your risk a failing valve and making a mess of your engine.

Do you have a hour meter on it yet? If not, buy one asap. Do you know how many hours are on it? Typically trail riding it, your top end should be good for a 200 -250 hours. At the MX track and as you get faster, that could drop down to as little as 50 hrs. Your crank/main bearings should last 4-500 hours trail riding... much less on the track as you get faster this could drop to as little as 100hrs.

Now that you have your MX track built, you are spending more time on it, and I assume getting faster each week...... you are going to have to start stock piling parts as they will become maintenance. Cranks (or crank/rod rebuild parts) main bearings, cylinder (new cheaper than plating on these YZ250Fs, dont bore or add steel liner) unless there is someone in Pakistan that plates cylinder - we only have a few in the states, timing chains, head/valve parts, pistons, and gaskets. All of these things are going to become regular maintenance items on it.

 

[KooLaid]

Sounds just like typical top end rebuild time.

 

[khan]

Moin -

Any 03 04 05 exhaust cam should work (it comes with the autodecompression on it, not seperate.) 06 -08 might even work. Ask same question on thumpertalk.com to clarify Even ebay if it looks good, ie no wear or discoloration on the cam lobes. RockyMountainATV tends to be a bit cheaper than Bikebandit FYI. OEM valves for your year of bike. Nothing changes with the new cam.

A few things. Now that it is running, you really need to do a leak down test on the motor. That or a compression test is going to tell you if need to do top end on it or not. If you dont know or think its around 200, I would rebuild the top end and then keep track of hours.

And as already mentioned, write down how much your valves moved. I assume it was your exhaust valves. Check them again in 15 or 20 hours to make sure they arent moving again... this is important. Dont wait until you dont have compression again or your risk a failing valve and making a mess of your engine.

Do you have a hour meter on it yet? If not, buy one asap. Do you know how many hours are on it? Typically trail riding it, your top end should be good for a 200 -250 hours. At the MX track and as you get faster, that could drop down to as little as 50 hrs. Your crank/main bearings should last 4-500 hours trail riding... much less on the track as you get faster this could drop to as little as 100hrs.

Now that you have your MX track built, you are spending more time on it, and I assume getting faster each week...... you are going to have to start stock piling parts as they will become maintenance. Cranks (or crank/rod rebuild parts) main bearings, cylinder (new cheaper than plating on these YZ250Fs, dont bore or add steel liner) unless there is someone in Pakistan that plates cylinder - we only have a few in the states, timing chains, head/valve parts, pistons, and gaskets. All of these things are going to become regular maintenance items on it.

Alright here is the latest!!
I rode all day on sunday and it ran great, came home washed the bike, lubed the chain, changed the air filter and parked it indoors..

Today i went out and tried kicking it and it wont start. and i can feel the compression is already getting weaker.

About the compression test and leak down test, i checked with my mechanic and he said he doesnt have the tools to do it.. Called a few more mechanics and they had no idea what i was talking about. there are no MX bikes here.

im going to look up youtube, and try to figure this out..

I got an hour meter with the top end kit but havnt installed it because i have no idea how many hours are on the bike right now. I bought it used 2+ years ago. I was thinking to rebuild the top end and then put the hour meter and then i would actually know more about my bike.

It a real pain in the ass to get parts to Pakistan, sometimes it takes months. I know someone coming from the Bay to Pakistan on the 29th. If i can somehow order shit rightaway, ill have my bike ready soon. So need some advice on what to get and from where.

Currently I have

1. Wiseco PK1241 77.00 mm 12.7:1 Compression Motorcycle Piston Kit with Top-End Gasket Kit
2. Yamaha Cam chain 94591-53114-00
3. Hour meter

I need
4. 03+ cam is THIS THE ONE that I need to get? Should I order from ebay or should I look someplace else? My research says 03 to 2013 cam will work for my 2002
5. Valves (steel or titanium?) i cant find OEM ones
6. Should i replace my clutch while im building it all up? THIS will fit my otherwise stock bike right?
7. I also need Fork seals one of the forks leak

anything else you guys recommend i should get?

 

[Junkie]

compression and leakdown aren't MX specific, it's a way of checking engine health in general

I'm told steel valves last a little longer but can't be revved as high

 

[khan]

compression and leakdown aren't MX specific, it's a way of checking engine health in general

I'm told steel valves last a little longer but can't be revved as high

Im guessing they have different names here then cuz the mechanics here were just confused