Question about 2004 Yamaha YZ 250 F

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I just replace a broken exahust valve on my 02 yz250. While I was in there I also replace the piston and rings. The bike had been sitting for several years by the time I aquired it. As a result I rebuilt the carbureator. The bike is back together but wont start. It had good spark, appears to have good compression, and seems to be getting fuel. Once in a while it will back fire throught the exhaust while attempting to start. I checked the timing marks to make sure that the timing was right and it seems correct. Theoreticaly the bike should start but it is not. Any help would be greatly appreciated.

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I would squirt some fuel in the cylinder to see if it fires, then if it does, blame the jets in the carb being set wrong. Get some fresh gas, and a new plug if you have one. The carb settings might be fixed but still wrong. If they are adj, take them all the way in, then out 1 1/2 turns, this should get it running, if the jets are fixed on the inside, they might need some deep cleaning, did you make sure they were real clean??? Poke a wire through them and blow through them?? Check it out.

Posted on Oct 11, 2010

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Posted on Jan 02, 2017

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A “very helpful” rating on this answer? Thanks!

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