20 Most Recent 2003 Yamaha YZ 250 - Page 7 Questions & Answers

The fuel to oil ratio is 32:1. So for 6 liters it would be about 175ml.

This engine holds one quart of standard Yamaha YZ 250 engine oil. The oil filter is located on the rear of the crankcase behind the suspension spring. The oil filter looks like a small metal can that is screwed into the top rear of the crankcase. On the bottom of the crankcase is the plug that will need to be removed to drain the oil from the crankcase. Anyone who owns this model dirt bike can complete this job in about 10 minutes.Read more: How to Change Oil and Filter on a Yahama 250F ' eHow.com http://www.ehow.com/how_6574975_change-oil-filter-yahama-250f.html#ixzz1hECQRtAn

Check your clutch basket for grooves. if so you will need to replace basket. I’m happy to assist further over the phone at https://www.6ya.com/expert/michael_18b4936ebf017b21

your float is stuck open in the carb. might just need a simple cleaning or you may have to replace the float valve assembly. The float itself may be broken causing the float valve to stay open.

hiya 4 strokeJohn

In brief - it is likely an air leak or it is running too lean. Perhaps the pilot jet is plugged or too small or you have a cracked intake boot or a bad crankshaft seal. All of these are good possibilities. Without more detailed info, this is the best diagnosis I can offer. If this was mine to fix, I would probably pull the jug, re-ring it, put a new plug in it, check the reeds, check the intake boot for deterioration, disassemble and clean the carb then fill it with clean, fresh fuel and clean the air filter. All of this would cost you about $20 in parts (if you leave the head on the cylinder) and take maybe 3-4 hours.

Spitting oil indicates that it is running rich. It could be down on compression which will cause it to run rich. The rings don't last forever in these bikes and need to be changed every once in a while to restore proper operation.I am betting you are turning the air screw to "adjust" it to run rich as you stated. This screw only effects the lower RPM - it is actually a fine tuning screw to adjust the low end - specifically the pilot and needle jet. It has very limited effect on the jetting above maybe 1/2 throttle. The proper way to alter the way the carb acts is to physically change the jets in the carb. The pilot is for lower end performance, the needle is for the lower-mid range and the main is for mid to mostly upper RPM range. The float level also plays into all this.To attempt to answer your problem - it could be that your spark plug is incapable of firing once it gets overheated. An overly rich mix will prevent it from doing it's job also and can burn a plug out. Try replacing it with a fresh plug and you might want to clean your air filter and check your compression. You should have at least 150PSI. I've seen bikes run with as little as 95PSI but they run poorly and are hard to start.Good luck!

the problem you have is the water pump bearing worn you need to replace the impelar bearing and seal

The leaking coolant is a sure fire sign that you likely have a blown head gasket or your water pump is not pumping water any longer and the bike is overheating.The leaking oil could be coming from your power valve vent - is it pitch black oil and is it coming from the front of the engine?What color is the oil? Are you sure its gear oil? Is the gear oil milky and foamy? Is the gear oil level high or low? Is there water in the oil?Sorry for all the questions - there are several things that could be happening here.

no it is not the same.

Tranny is closer for yz
YZ has no lightning coil
intake system is far different from both.

BUT fitting is the same, so switching from one frame to another may be doable.

The factory recommends 15PSI. I usually run 12PSI.Depends a lot on what tires you have and what kind of "track" you are riding. You typically want a firm tire (more pressure) for a soft surface and a softer tire (less pressure) for a hard track but there are always exceptions depending on the details of the track and what tire you have mounted up. If you are riding a track with a lot of hard braking bumps or firm ruts or even tree roots (if you ride trails) you should run more pressure - like maybe 13-15PSI. If you run less than about 10PSI you risk pinching the tube and getting the rim damaged from sand intrusion between the bead and the tire which can cause a lot of problems unless you change your tires frequently and run multiple bead locks. To run really low pressures usually means you don't have the best tire on your bike for the conditions in my opinion. To simplify:Soft track, hard tire - run 12-15PSIHard track, soft tire - run no less than 10PSI

depends a lot on the track, soft loam can be down to 8-10 lbs, hard pack fast 15lb if there are lots of rocks etc and punctures could be a problem or very high speed 18-20

This is completely normal. It's nothing to be concerned with.

Your description is classic for a bent shift fork. The entire engine/transmission must be torn apart to get to the forks. This repair is not recommended for the home mechanic.

Just a question but are the valve clearances correct 0.20 exhaust and 0.10 on all the intake side?
also I would be double checking the decompression lever mechanism with the valve cover off you can see it pushing down on the valve bucket when activated double check it is lifting off the bucket when de activated as sometimes they stick and keep the exhaust valve hanging open a little
with the cams out you should be able to spin the buckets with one finger. are they moving nice and freely?
with the cams out you should be able to push each bucket down if you push nice and hard are they moving freely and springing back up nice and freely
My last bit of advice is a compression test is next to useless on these motors for diagnostics - you need to do a leak down test to get any real info once you pressurize the cylinder listen for leaks out the exhaust or the intake port or the oil filler plug hole this will tell you exactly where leakage is if leakage is the issue
good luck let me know if you want more info on specifics
regards Jamie

Yes, the case will need to be split. The problem is likely to be a bent shift fork. A bent fork can stop the dogs on the slider gear from fully engaging in a gear. If the problem turns out to be a stripped gear, you need to replace BOTH the stripped gear AND the gear the bad gear meshes with.

There's a few areas of concern here but by far the most common for older YZ is the stator has low or NO resistance there for does not generate when kicked over
I am assuming you have tried new plug before posting your question?
it is very easy to test stator if you have a reasonably decent multer meter let me know if you want more info on testing or you may wish to take to a shop and they test it for you... Good luck!

Hi mate I would be getting someone to check resistance on your stator its a simple test only requires a multimeter but hard to explain on here - From what your saying I think this test could save your headache!
Once stators fail they can be completely unreliable such as allow you to push start but not kick start or allow you to start but as soon as bike warms up fails completely until cold again they even can give false reading when you test to see if spark is at the plug as you see spark but is not strong enough or is sparking at wrong time... I have had bikes come in my work shop where guys have been confident has spark and they have rebuilt and replaced everything you can imagine but all it was the stator failing with not enough resistance..

regards Jamie

This is the tell tale hole that lets you know the pump seal is gone, if you plug it ,water will eventually push past the oil seal and end up in the engine

hello
with the cylinder set at top dead center compression. using a feeler gauge between the tappets and the valves there should be .002-.003in clearance on the intake valves, and .006-.007in. clearance on the exhaust valves. thank you.