yamaha 90 drops rpms

tiredboater

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Aug 11, 2011
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I have a 2002 yamaha 90 tlr with about 200 hours. I have always ran it regularly and use stabilzer. Running wide open 5000 rpms after 5-10min it instantly drops to about 1200 rpms. Turned off motor restarted and ran wide open again for a couple minutes and repeated problem. Motor sounded funny so I Checked and found running on only top cylinder when this was happening. It has spark on all cylinders. Just had carbs rebuilt at shop. Replaced antisiphon valve and pickup tube, new primer, and water seperator, completely drained tank and refilled. Didn't fix it. Any ideas? Could this be a weak fuel pump? Could an ignition componant be failing only at wot? Choke didn't help. Disconnecting the emergency circuit had no affect. I'm stumped and tired of working on this motor.
 
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