20 Most Recent 2003 Yamaha YZ 250 - Page 6 Questions & Answers

I have always had great support from yamaha in regard to engine building assistance. If you goto yamahausa and use the contact us field with a request for the benchtop procedure for assembling your yz250, they are willing to send it to you at not cost if you are persistent

You might find a free pdf service manual on this site, they have a ton of them.
http://www.carlsalter.com/motorcycle-manuals.asp

or try your local library. Often guys will donate manuals to the library.

Please rate this solution. Thanks wikusnagel!

Hi mate this will be the oil & water seals the leak from weep hole is basically a warning light to tell you it needs replacing asap, you need to remove impellor, carefull not to lose the spacer washer behind it...then remove the water seal clean the surface it came from and replace with new seal. Now to do this 100% I would always replace the impeller shaft as the shaft wearing is usually what caused the seal to fail and I would also replace the oil seal which is the other side of case that you just changed the water seal (oil seal sits behind the small bearing) I would also consider replacing this bearing but maybe not critical? all up the impellor shaft the 2 seals and bearing last time I bought cost about $160... no special tools required just quite a bit of time required as you should really remove the outer engine case to access the impellor to undo it and to get to the oil seal and bearing, how ever I know guys do just open the water pump cover then rattle gun off the impellor only replace the water seal then install the impellor and cover back on then ride away! this will work and will fix the leak but is definitely the incorrect way to repair this and will be temporary fix but thought you may like to know this alternative as is very handy way to do it if your on a race meeting and just need to get through the last race or two. hope this help cheers... Moto X Parts online.com

Not sure of the age of your YZ 250 ( You never said!) but in most Yamaha they use dual stage stator which means a stator will charge a spark plug at two speeds one on kick starter speed and the other on running speeds it is common that the low speed circuit on the stator to fail leaving you with a bike that only starts when pushed its a very simple test to diagnose it be worth checking you have spark on kick starter speeds with spark plug out the motor but still connected

similar/same?? rate me?

http://www.mxguy.com/motorcycle-maintenance/2003-yamaha-yz250f-service-manual_01-16-2008/

More than likely the majority of the problem is related to poor compression pressure. When was the last time the engine was re-built (a new top end)?

I would suggest evaluating the condition of the piston, ring and cylinder. Replacing the piston and ring and won't set you back much if the bore in the cylinder is good and it will definately perk your bike back up.

Clean that air filter too - a plugged filter will cause the bike to run rich, too.

spark plug brand i am using is an NGK IRIDIUM IX (BR8EIX) number 3669 fires up first time everytime i have a yz 250 1995 model aswell

Check the compression. It should have at least 100 psi,..if not,then its time to rebuild the top end..IE piston,rings,bore cylinder. If compression checks out,i would start with the power valve. Two stroke dirtbikes power valves are notorius for gumming up and sticking,causing them to not rev correctly.

fuel problem take out the carb and clean all the jets and the bowl also put a high flow fuel filter in as a precaution incase there is debree in the tank your problem is that you are not getting enough fuel or any at all. If you need further help, I’m available over the phone at https://www.6ya.com/expert/brandon_79b580f5a99c4386

This is a sealed carb and no adjustment is needed or provided for except idle speed.

check the exhaust carbon builds up inside and restricks the exhaust flow

Maybe not your answer but.If the bike has sat around for a while,the clutch plates can stick together.Not all,but some.This makes gear selection hard and as you describe,once things warm up,it gets better.When I said about sitting around,I meant for a period of a few months or so at one time.Hope this helps

A shft is broke or bent bad or a bearing got real hot and welded itself to the shaft. If you can roll down a hill and put it in gear and jump it off its one of the two prior problems. it it want start the motor might be seized up.

you got a blown head gasket or warped head

Pretty sure in late 80s early 90

Replace the reeds, Clean the carb jets and adjust mixture screws.


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no but the plastics are interchangeable. Possibly someone has changed them due to damage?

First place I would look after all the obvious such as spark plug good fuel good reasonable compression if the bike starts fine and runs for few minutes then dies the number one issue I have seen to do this would be the stator they have high speed and low speed circuits in them and if the high speed circuit is failling the second it warms up a little you will lose spark at the plug there is very simple test to check the stator but is difficult to explain here you need in short the OHMS reading form the stator

so, can you tell me what kind of carb was on the bike before? was it factory? and what kind of carb was just installed? blue smoke can be caused by burning transmission oil or a rich fuel mixture. that might be a bad crank seal or case gasket, or just improper fuel/oil ratio or improper jetting. black smoke on the other hand is usually caused by too much gasoline burning, but if there were enough gas entering the engine to cause black smoke, the bike probably wouldnt run at all. but, if you can give me more info on the carb swap, and if possible any jetting information or jetting changes, thenI can definitely tell you what your problem is.

Unscrew this. This is your dipstick.