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Loss of Power? Please Help

Old 05-22-2019, 09:08 AM
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Question Loss of Power? Please Help

Hello all,

I am running a 98 Yamaha Vmax 150. Last week I was running to a fishing spot at WOT and the boat was running perfect (about 57 mph with a loaded boat and two people) I had to slow down to adjust my angle going under a bridge and ever since then the motor runs slow/sluggish. The boat would only reach 50 mph the rest of the day with the same load. This boat typically has one of the fastest hole-shots with this motor and now it drags out of the hole as if it was weighted down with water. Fuel line is brand new, spark plugs are new, fresh tank of gas, no signs of a spun hub, livewell & bilge are dry,nothing stuck in foot/prop, throttle position is accurate, RPMs sound low (gauge has never been accurate so hard to tell). ANY advice/thoughts will help.

THANKS IN ADVANCE!
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Old 05-22-2019, 09:11 AM
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new fuel filters
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Old 05-22-2019, 09:18 AM
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This motor has an in-line fuel filter assembly. Are you suggesting that I need to replace the whole assembly or just a filter within it?

Thanks.
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Old 05-22-2019, 04:03 PM
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I've been running a 20 year old motor flat out for years.....
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Old 05-22-2019, 04:41 PM
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Originally Posted by billinstuart View Post
I've been running a 20 year old motor flat out for years.....
I am struggling to figure out how this helps me...
​​​​​​
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Old 05-22-2019, 04:51 PM
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Took apart the fuel filter assembly today. Filter is clean, in good shape, no cracks in the housing, O-ring is in good shape and the entry and exit stems are clean. Could it still be the filter? I also checked every fuel line from the tank to the filter. All of them have no visible damage and appear hold pressure while allowing steady flow. Wondering if I should chase this into the two fuel pumps?

Thanks again for any advice/thoughts
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Old 05-22-2019, 05:47 PM
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Are you still getting full throttle,carb plates fully open
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Old 05-22-2019, 05:49 PM
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To my knowledge yes. I can manually move the throttle and the flaps open (motor not on).
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Old 05-22-2019, 05:55 PM
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Default loss of power

head gaskets? Carbon build up?
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Old 05-22-2019, 06:09 PM
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Sounds like a partial fuel blockage somewhere.
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Old 05-23-2019, 04:29 AM
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Originally Posted by billinstuart View Post
I've been running a 20 year old motor flat out for years.....
after decades of abuse, stuff happens.
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Old 05-23-2019, 06:41 AM
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Also.. check your plug wires and spark. I had a motor do the same thing. Turned out one of the boots on the wire was bad. New set of wires and all was good.
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Old 05-24-2019, 08:01 AM
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Ok I have several things to check this weekend thanks for all of the suggestions. I will let you know know my findings.

Thanks again.
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