SOURCE: i bought dirt bike for husband! is 2005 yamaha
Congrats on the purchase! easy way to tell look at the exhaust pipe. if it is just a thin tube that is tight to the engine and goes right to the muffler it is a 4 stroke (250f). the four strokes have a square-ish head. Deep/bass-y engine sound. If you have a large (probably black) exhaust pipe with a large bulge in it (5-6" diameter) that wraps around the front of the frame, its a 2-stroke. They have a more round cylinder head. Beautiful pingy sound and a little smokey at start up. DON'T FORGET TO MIX YOUR GAS!!! there should be a serial number sticker at the very front of the frame (behind the number plate where your triple clamp/handlebars connect) Probably on the left side. Hope it helps! rate please :)
SOURCE: i have a 2004 yamaha yz250f it will only start with starter fluid
check the carburator if there is a gas goes to it
SOURCE: My Yamaha yz250F 07 starts first kick but back
I see: you changed the plug because it was backfiring.
Does it back fire when you let OFF the throttle after revving it, or does it back fire while being revved?
If it does it when you let off then Ollie's suggeston might do it. If that doesn't do it then check for dirt in your pilot jet.
If it back fires when revved up high could be dirt in your main jet.
SOURCE: I have a 04 yz250f, it started fine when I bought
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
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