Question about 2004 Yamaha YZ 250 F

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I have a 04 yz250f, it started fine when I bought it 3 months ago. I let it sit for about a month and could not get it started. I changed the plug and put fuel stabilizer and added fresh fuel thinking that it was bad fuel. Finally got it started after many tries by push starting, rode it hard for 25 min. and put it away.Tried to start it the next day and can't get it started?

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It does sound like a fuel problem, but a month is not really long enough to cause fuel problems. My suggestion is to make a few checks first to verify the problem.

First, make sure you are only using premium fuel. These bike require a hot fuel to run properly. Take off the seat and check the air cleaner. Dirty, clean with soapy water, dry, and put back on, or replace.

Remove fuel tank and remove your spark plug. If it is covered in black soot, you are running too rich, if burnt, too lean. (This is usually accompanied by deceleration backfires in YZ's) If OK, put the plug into the coil piece and ground against the frame. Kick the bike over and make sure you are getting good spark.
If ok, put it back in.

Remove the screw at the center bottom of the carburetor. I believe it is a 15mm. Check for debris. If there is any, you will need to take off the carb and have it professionally cleaned. Details on how to do that is as follows: If you take it off yourself, I usually get mine done for $25. If you take it apart, be sure that you only remove the bowl. The secondary bowl of this carb is injection molded. The screws to take it off are security star screws. Do not remove them. Once taken apart there, it can pretty much be thrown away, and you can buy a new one for about $300. Never remove star security screws. They are there for a reason.

Shut off fuel
Take off the seat(2 12mm bolts)
Remove strap to fuel tank
Remove bottom bolts to radiator fairings (10 mm)
remove fuel tank frame bolts (10mm)
Disconnect the fuel line and remove the tank. Clean it by dumping the fuel and removing the fuel shut off switch. Check the screen for debris to determine just how dirty it is. Then just clean it out by running water through it till it comes out clean. Turn upside down with fuel cap off to allow to drain and dry.
Remove Hot start choke (14mm open end wrench)
Note: Be very careful removing and putting this back. It is made of plastic and strips extremely easily. If you do strip it, I recommend buying a replacement for it made of aluminum. About 5 bucks. Once unscrewed just lift it strait out of the carb.
Remove carb side cover on right side of bike. (4mm allen wrench)
Remove bottom throttle cable first by loosening the 10mm nut, then slide out. unwind it from the throttle wheel and pull it sideways from the wheel through the slot.
Remove the upper throttle cable. Unscrew the nut to it with a 14 mm open end wrench. Unwind it from the wheel and remove it the same way as the bottom one.
Disconnect the tps sensor at the wire connector. DO NOT LOOSEN THE SENSOR FROM THE CARB BODY! This is set by the factory.
Loosen the front and rear boot sleeves to the carburetor. (Sometimes a 3mm allen wrench, or 8mm bolt)
Push the entire carburetor towards the air cleaner, twist to the left side of the bike and work it out of the bike.

If you take the bottom bowl off yourself follow these steps.
Get a small plastic baggy for all small parts so you don't lose anything.
Take note of the placement of the air tube screw locations
Tilt the carb upside down over a small bowl. Fuel will leak out.
Unscrew the bottom of the bowl. (Phillips head)
remove bottom bowl, and place screws and bowl in the bag. Inspect for debris.
To remove the air mixture screw, lightly tighten it all the way in and record the exact number of turns as this is also set by the factory for optimum performance. Once complete, unscrew it completely from the body while holding it over the bowl you drained the fuel into. On the screw there will be a rubber o-ring, washer, and a spring in that order. Remove

Posted on Sep 07, 2010

  • bra1nr0t Sep 07, 2010

    I ran out of room. Remove the main jet and pilot jet. (Just turned all the way in so no reason to record the turns. Place these in the bag, take it to have it cleaned. Follow these steps in reverse to put back together.

    If this does not resolve your issue, you do not have a fuel or electrical problem. The only thing left is compression.


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Go up to ur closest shop and buy a lighter. When you have done that go back to were ur bike is. Once youre there put a bit of cloth in the petrol tank, take it out then put it back in (other way round). Then light the cloth then run!!

Posted on Oct 19, 2012

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