Question about 2002 Yamaha WR 426 F

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Just bought WR426F bike and its been bored out to a 450. I can't seem to start it. Is there a nack to starting it and is there a on/off swicth that I don't know about. How hard do you have to kick it to start it. It also has a tapping noise when she's running. Is this normal? Any help would be greatly appreciated. Thanks

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01 and 02 are a very hard start. electric start? ya need to give me a little more about the tapping. top end? does it tap in rythem with the rpms? could be shim adjustment is needed, the valve shims could have the snot pounded out of them. can you give me more info

Posted on Apr 11, 2011

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  • ney4655 Apr 12, 2011

    Hi airbornekniv: electric start? No, Kick Only. ya need to give me a little more about the tapping. top end? Yes. does it tap in rythem with the rpms? Yes . Very load at start but as she warms up the noise reduces but still can hear it.
    Camshaft is very tight and it looks like the top end is from a 450cc. The bloke I bought it from has only done 45hrs on it since top end modified. Hope this helps. Thanks

  • scott horn Apr 12, 2011

    is it blowing any smoke at idle or start up? if so what color is the smoke, does it smell like oil or dose it smell like sound like you need to check cam gap....almost have to hear it...if i had the bike here i would do a leak down test on it and check the gap between the cam lobs and the buckets...and i dont think it has a head from a 450....2003 they made the 1st generation 450 and the head is a different part number than the 426 head, so the guy that sold it to ya might be pulling your leg about the head. if you go on ebay you can order a factory oem manual on cd-rom for about $ you will need a manual to check specs. also if this is your first 4 stroke bike, keep in mind the timing chain is kinda loud on the yamaha 4 stroke, you might be hearing that as well. but i would check the gap before you burn up the far as the hard start goes, if you have a decompression lever on the handle bars use it about half way to release some compression while kick starting it, it will make for an easier start. and if you have a decompress lever that means you probibly have a 2002 426f head, because a 2003 450f head has an auto decompression cam and thus no lever... . another thing that will help start the older yz's is the spark plug...your bike takes an " e8" spark plug. i would go to an "ek9" it is one step higher in spark temperature and it is a double prong spark plug, and just going one step higher in temp, wont hurt the piston, but i wouldnt go any higher than that. also make sure the piston is at the top of the cylinder before you kick start it.....give the kick starter a couple short easy kicks, you will notice that the stroke gets a little shorter and a little shorter until it is suddenly hard to do any it is ready to kick start...squeez the decompress lever about half way and give it a hard kick all the was down, make sure the choke is on. always make sure you are at the top of the stroke before you kick start is.

  • scott horn Apr 12, 2011

    you should be able to get a manual here for free

  • scott horn Apr 13, 2011

    did that help you?

  • ney4655 Apr 17, 2011

    thanks mate I put the bike in for a full service and after $350 later got told that they have adjusted the valves but the cam chain is to tight and they aren't able to adjust it. Mechanic tried starting it without success. They have put bike together and don,t want to touch it. I will pick bike up on tuesday and let you know.
    Thanks for your info and I will be trying your suggestions soon as I get it back.

  • scott horn Apr 17, 2011

    there is a part number on the head. call your local yamaha dealers parts department....ask for the part number for a head for a 426, and aske for the part number for a head for a 450f. it really doesnt make sence that they told you its to tight...maybe the guy you got it from did change the head....maybe a timing chain from a 450f would give the extra slack needed..its a head scratcher thats for sure....let me know what ya find out.....maybe wrong cams? who did you take the bike to this last time



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