Question about Yamaha WR 426 F Motorcycles

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My daughter has a yamaha Raptor 90 2009. I had been having major dramas with the orginal carb and have removed it. I have replaced it with a carb of a 2 stroke of the same cc and have put the same size main jet in. It seems to pull ok down low but when at full noise at speed it pops and lacks power. I have tried the needle at all positions and have played with the air mixture screw but it still does it. Please help

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  • brett_wortle Jun 02, 2010

    Thanks Mate I'll have a play with it and see if it improves



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The mixture is too lean at high revs. Put the needle at the most retracted position and don't touch the air mixture screw, it acts only at (and near to) idle speeds. You need a bigger jet, probably the original one on the carburettor.

Posted on Jun 02, 2010

  • brett_wortle Jun 02, 2010

    I have tried the needle in single increments to the middle position and its seems to get worse not better.

  • Azrael SRL Jun 02, 2010

     The needle gets thinner towards the top, this is to increase the fuel flow. So put it  not in the middle position, put it all the way up. You will know when there's too much fuel by the black sooty smoke on the tailpipe. If necessary you should even raise the level in the fuel chamber.



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