It sounds like you aren't getting gas.
Make sure that the fuel line is delivering fuel.
Disconnect the fuel line, get a safe container, no smoking, turn engine over and ensure gas flow.
Gary
Question edited for clarity, and add maker, toss in some CAPS.
Question moved to model category.
Mating surfaces not flat and true.
Reinstalled without a new gasket.
Under torqued or unevenly torqued.
No gasket goo used.
https://www.google.com/search?q=2001+Yamaha+YZ250F+valve+cover+gasket+leak
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If the plug wires are more than a couple of years old, I would replace them. You don't say where you are. If you are in a dry environment my answer might be different than if you are on the coast or near a large body of water.
When you say you've "played with the idle screw", do you mean the idle MIXTURE screw, or the idle SPEED screw?
Also, it COULD be the throttle cable.
At idle, is there a LITTLE slack in the cable, so it's not pulling on the slide/butterfly crank?
Or, it could be cable routing, hanging up on something.
Finally, has the cable ever been lubed?
If you mean piston ring, then you will need to check the cylinder bore for scoring. If you mean the head gasket, then you will need to replace the gasket and make sure the mating faces are flat, Use a metal Rule to check this. If it is flat, you can just re assemble the top end. 2 stroke engines are exceptionally easy to maintain, as you have the head off you can check that it has been decoked and that the piston is in good (clean) condition.
Yes two ways, if it is not a hydraulic system there is a lock nut located at the end of the rood that connects to the brake housing turn this lock nut two turns to the right and test the pedal this will bring the brake pedal higher, keep doing this until the desired brake feel is achieved but be careful not to go too far you do not want any brake drag it will burn of those new pads. If it is a hydraulic system you need to bleed the brake system and if you are not sure how to do this consult your local dealer for instructions or better yet have them do it, this does not take long and is not very expensive best to leave that one to the professionals for your safety, hope this helps.
Hi, if you have an owners manual then would be really easy, if not... It depends on what year, you can look up the manual on how to do it by the year of your bike.
or there's another option by looking at this video so you can have some ideas.
Hope would be easy for you.
Thanks for using FixYa.
your info is a little vague, is it a popping or a loud bang backfire? popping is normally due to air entering the exhausts usually due to exhaust loose or gasket faulty where it joins the cylinder head.backfire is due to a number of things ie timing being out.
It sounds to me like a part is missing in the clutch assembly. Bear in mind that the first plate installed in the clutch assembly is a cork friction plate, then metal, cork, metal, ect.. You should end up with a cork friction plate. There should be 6 metal plates and 7 cork friction plates. The diagram below is a tri-z 250. Please rate my answer. Thanks!
sounds as if the cam and bearing sizes are mismatched, you dont say if this is a rebuild, with new parts or with originals. you also dont say if you have fitted exhaust cam yet you also dont give make and model.
first of all, after the bike starts release the choke, you dont want leave the choke on until it gets warm, because it makes it a really rich mix, and it will eat the oil off the cylinder wall and you can burn the rings and cylinder wall. try this. at the bottom of the carb is a fuel screw(small standard flat head screw) turn it all the way closed, then back it out 2 full turns, that should give you proper mix, right now your running way to lean, thats why its working with the choke in. has anything been done to the bike? new after market exaust? if so it could be a jetting issue. and you are correct about the hot start.....there is a little rubber gromet on the barrel of the hot start plunger where it goes into the carb, that washer could be bad, or the black plastic boot that attatches the hot start to the carb could be bad and is allowing air to be sucked in...but i would reset the fuel screw on it first....hope this help. if not, repost and we will get ya figured out. p.s. nice bike.
Its not common with YZ but is very common with not starting the bike for long time - you need to take out the pilot jet and replace it with new, You could clean them but why bother they about $5 each?
If I were you whilst you have the carbi off I would change all the jets to new ones especially as been sitting for a while (not essential but worth while as off already?)
running only with choke on and backfire are classic symptoms of blocked pilot jet or incorrect size pilot jet so chuck new one in and you should be good to go
The pilot jet is the jet closest to the engine when carbi was installed (it has perforated holes on the side)
good luck regards Jamie
Check the diagram below to be sure all parts are present. The nut should be tightened to 43 foot pounds torque. Be sure the lock washer tab holds the nut in place.
