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Yamaha 115 4 stroke

The injectors may not be firing on all 4. Remove spark plugs and check them. If it's white then it's running lean -> not enough gas -> injector clogged or not firing. Do these tests with an external fresh gas tank to rule out bad gas. Get a noid light to check for electrical pulses get to the injectors. If you have injector pulse and not firing means the injector selenoid is stuck. Take a screw driver tap on it lightly while cranking. Some times it breaks lose and starts working again. I had this happened many times if you let the motor sits too long without running. Good luck.
 
harleynana said:
Have Yamaha 115 4 stroke motor. Fuel pressure steady 45# motor loses power what could be problem
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I have a Yamaha 2001 F115. You said fuel pressure is 45 PSI but motor loses power. If you have a fuel gage I assume you know how to check for plugs firing and have eliminated that cause. If I were to guess, it probably idles OK and runs OK until you try to feed her some gas and then she kind of boggs down, runs rough and not much power. I think you probably are using ethanol gas and have all the fun we all have with it with fuel restrictions somewhere. Thank you Government for this ethanol in our gas! You can have all the fuel pressure in the world but it either isn't isn't making it into the cylinders or that pressure is taking a long time to build. IF you have the gage hooked up, take her out, put the throttle to her and see if it drops in a serious way which would mean a clog before the outlet of the VST pumop. If you can't do that, I'd bleed off the fuel pressure in the fuel rail (there's a screw) retighten and then take the high pressure fuel line off the bottom of the fuel rail and point it out somewhere where it can squirt into bucket to catch the gas. NO SMOKING! Now, turn the key only to the "on" position and you should see it to squirt a good deal of gas out of it and it should keep on flowing at a high rate... The VST pump comes on as soon as the key hits the ON postion to build pressure before you reach the "Start" position. If you get a good strong flow in just the ON position, it is one or more of the fuel injectors that needs cleaned. You can try to clean them yourself backflushing with a can of carb cleaner and roach clips hooked up to the battery to open and close the, over and over as I tried (google DIY fuel injector cleaning) or you can send them to fuelinjectorman.com who had the best deal on the internet that I found. If you don't get a good strong flow or you see that pressure drop when out in the boat putting the throttle to her you have a clog up line. Take off the outlet side of the little fuel filter on the left hand rear of the engine under the cowling and have someone watch while you squeeze the fuel bulb. NO SMOKING. With each squeeze there should be a shot of gas smooth and full come out of that line. That would eliminate the Racor and the little filter in the back of the engine. IF no big squirts, time to replace those. IF those are clean you are on to the FUN job of getting to the filter in the VST tank of the F115 and changing that little filter inside. It is a like a $35 filter but the Yamaha mechanics will charge $500+ because it is a pain the butt to get to. Others have posted how to get there and I've done it myself. 1st time takes 5+ hours to get in and out because you'll spend over an hour trying to get that lowest nut off the intake. Second time, 3-4 hours.
 
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