150hp Yamaha carb or fuel problem

On Island Time

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Oct 17, 2008
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Yamaha S150TLRW, 1998. Just purchased four weeks ago in great condition, except this.

Problem is: At around 3000 rpm, pushing throttle down quickly, engine hesitates for a moment or so, and then takes off. From idle you give it quick-full throttle it does not happen. Carbs have been soaked, cleaned adjusted, etc. Fuel pump diaphragms, also replaced. Fuel system, vacuum tasted under load. New fuel filter and clean gas.

I heard Yamaha had a bulletin concerning this, about "flashing" in the carb.(?) My first time posting, any thoughts are very much appreciated. Thank you.

ADDITIONAL INFO: Carbs have now been flow tested and flashing removed, but the same problem exists.
 
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