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2003 yz250f wont start after rebuild

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hi,ive just had my yz250f rebuilt,new crank,conrod,piston kit,main bearings,cam chain,cam cushions,the problem is before i had it rebuilt it started after about two three kicks and ran fine but since i had it rebuilt i went to start it (after i made sure thier was oil circulating)it started and ticked over for about 3 seconds and then abroubty stoped as soon as i went to blip it,i tried for about a hour or two to restart it but it wasnt even trying to start,took out the spark plug and it was wet,bought new plug put it in the next day tried again to start it but on about the fourth kick back fires once ,has anybody got any ideas what the problem could be as i am really pi**ed off as it cost me £643 to have it rebuilt and i am now left with a bike that wont start,cheers in advance

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hi,thats what i thought the valve timming might be out a tooth or may be valve clearance's,but according to the guy who rebuilt it said it cant be out ???,when it started and ticked over for the 3 seconds i cant remember if it sounded like it was missing though,cheers for the advice,take care

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hi just been thinking,would it still have compression if the valve timming was out,as it has very good compression ???,also after it cut out every time i went to kick it spat out a tiny little bit of petrol from the overflow pipe on the carb,i thought at first maybe sticking float valve but had that problem on a yz250 and seem to remember the petrol flowing out instead of just spitting a tiny bit ????.please any help or suggestions would be much appreiciated

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The most common mistake when setting timing is setting it with the chain tensioner out. This creates unnoticeable slack between the cams, so it looks like it is timed right, but when you put the tensioner in you see the intake is off by one tooth. If you do not double check the timing after you put the tensioner in, this almost always happens. If the intake timing is off by one tooth it will have a hard time starting, and will sometimes start and run very poorly.

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The most common mistake when setting timing is setting it with the chain tensioner out. This creates unnoticeable slack between the cams, so it looks like it is timed right, but when you put the tensioner in you see the intake is off by one tooth. If you do not double check the timing after you put the tensioner in, this almost always happens. If the intake timing is off by one tooth it will have a hard time starting, and will sometimes start and run very poorly.

Call me stupid, but I had that happen a couple times with my 450. It is very easy to be off a tooth and have it look just right. I poped and would not run. I took it all apart and found the error. It is easy to check.

Won't the guy that did the rebuild check it?

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hi,cheers for the advice guys,i took the valve cover of last night and all timing marks lined up,took it back to the guy who rebuilt it he had a visual look over it and noticed that the plug that plugs into the coil had the wire insulation missing right at the bottom of the wire where it enters the coil and he thinks that that is causeing it to arc across the wires and making a weak spark,i have now got another two pin plug which i am going to put on tonight and try to start it,lets hope and pray it works,if it does i will update this post to let you all know,cheers,take care and all the best

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UPDATE: hi,ive just fitted the new two pin plug that plugs into the coil and

thank god,my bike burst back into life(what a weight off my shoulders)oh man i had visions of having to save up and spash out loads of money on the valves and miss the last of the good weather(if you can call the weather we get here in manchester,england good that is),before i go i would just like to say thanks to the people who took the time and effort to replie to this post,so thanks to zookrider98,kj790,and bbrown626,take it easy and all the best

chicargo

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