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2003 yz250f won't start

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Hey Guys I need some help, I am working on my buddies yz250f and it will not start the valve clearance is in spec the timing is spot on verified the piston is at true TDC by probing spark plug hole, verified bike is getting fuel and spark however on the carb itself the fuel screw is missing the rubber oring and Spring and will not seat properly, the bike doesn't even attempt to start while kicking however bump starting it in 4 and 5 gear it does try to start when in 1st 2nd or 3rd though it just locks up the rear tire this is a 2003 so it has the autodecomp unlike 01 an 02. Anyone have ideas?? Thanks I'm lost

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You need the o-ring on the mixture screw. It's sucking in too much air. Get a new spring and o-ring and go from there

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Thanks that's what I was thinking but however when we tried to bump start in 4th and 5th it was smelling rich as heck. Suckin too much air would be lean. I'm lost with this one

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you might want to check the valves again my buddy had the same problem with a kx250f the valves where bent and the only way to start it was to pop (bump) start it. but start with the fuel screw first.

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Look that's exacty what I was thinking and no there isn't, it is Gettn spark for sure timing is dead but not with the flywheel because when the flywheel says TDC the piston is like halfway up in the cylinder which leads me to believe bottom end has had work done to it and flywheel not put back on right

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dose ur book say thier is 2 marks right next to each other or just one mark cause my buddy had to look for 2 marks and we kept on setting it on the 1 mark and it was the same as u the piston would be half way up

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k then i dont know what to tell u bud im stumped sorry if i find anything else out i will post it on here

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Thanks buddy can that fuel screw cause not to run I mean that makes sense

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the fuel screw needs to be properly assembled (and the o-ring not squshed up into the hole) and set at 1.75 turns out from lightly seated.

yes it is kind of important.

however, a plugged pilot jet will also not allow it to start. a new one is highly advised.

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If the pilot jet were clogged were the plug still have fuel on it??

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You can find TDC by sticking something down the spark plug hole and feeling for TDC. Make sure you get the stroke with the valves open if you are checking for clearance.

Like I said in the other thread, the fuel screw is very important to starting.

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I already did probe it by sticking a long Allen wrench in the plug hole and, why would I check it with valves open Valve clearance is only To be checked at TDC of the compression stroke because all valves are closed

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Ok so I pulled bowl off the carb and the spring from the old fuel screw was stuck in ther putting it together now hopefully it starts

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Still won't fire up but the hot start is broke off in the carb we found out

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