Yamaha 40 hp poor performance under load

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bikerboy97229

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Joined
Jul 23, 2009
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Yamaha 40 ELRP 6H4 l 422248 The year is 92 or 93, original owner. Motor has done a lot of sitting. Decided to not take chances so replaced fuel tanks, fuel, and battery. Started up at home, checked to see it would go to 5000 rpm's and shut it down before heading out to the water. On the water under load cannot achieve rpm's over 2700, barely enough to go 10 mph. Normally can go 30 mph. Something wrong. Plugs replaced, fuel filter removed and cleaned, all plugs have spark. Noticed middle plug seems to be wet with gas and there is some minor misfiring happening. Sprayed carb cleaner in carbs, not much help, drained carb gas. Problem still exists. Motor has low hours for its age. No parts have ever been replaced. What should my next course of action be? I do have many tools, lots of time and limited income. Located in Portland, Oregon. Thanks in advance! :)
 
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robert graham

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Joined
Apr 16, 2009
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6,908
Re: Yamaha 40 hp poor performance under load

almost a sure bet that your carbs are dirty and need to be removed and cleaned. a shop can do it for around $130+, or you might can do it yourself. I've never done a carb cleaning, but before I would try it, I'd buy a Yamaha shop manual, which you can buy on line under Yamaha Outboard Parts. Good Luck!
 
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robert graham

Admiral
Joined
Apr 16, 2009
Messages
6,908
Re: Yamaha 40 hp poor performance under load

one other thing, after you get carbs cleaned and set, buy a water/fuel seperator at Walmart $27, install on your transom(very easy to do), start using the Stabil Marine Fuel Stabilizer all the time, and you'll eliminate most fuel related problems. Good Luck!
 
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