2004 Yamaha 115 Four Stroke Starts/ Runs fine to 4000 RPM Won't plane off.

Angie P

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Apr 2, 2015
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Last summer my son ran out of fuel and the boat has never run right since. It will start and run fine till you get up to 4000 rpms. Then it bogs down and will not plane off. We have replaced the fuel pressure gauge, cleaned the fuel rail, cleaned the fuel pump screen, had the fuel injectors cleaned and checked. Running out of ideas. Could it be the high pressure fuel pump??
 

99yam40

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Sep 7, 2008
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Last summer my son ran out of fuel and the boat has never run right since. It will start and run fine till you get up to 4000 rpms. Then it bogs down and will not plane off. We have replaced the fuel pressure gauge, cleaned the fuel rail, cleaned the fuel pump screen, had the fuel injectors cleaned and checked. Running out of ideas. Could it be the high pressure fuel pump??

What does the fuel pressure gauge say the pressure is running at while problem shows up.
By the way I have never seen a motor with a fuel pressure gauge in it.
 

Angie P

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Apr 2, 2015
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Whoops. Fuel pressure regulator. I haven't seen one with a fuel pressure gauge either. With the boat running the gauge reads 40 or 41 PSI. If you turn off the engine the pressure slowly declines. We haven't had an opportunity to put the gauge on it in the water. Really stumped on this one.
 

robert graham

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Apr 16, 2009
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Maybe one injector screen is partially plugged....just because they were cleaned before, they may have some trash on them now....I've had a 115 4 stroke do exactly what you describe and it was a screen....about 4000 RPM's and she's running on 3 cylinders....
 

99yam40

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Sep 7, 2008
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if you do not test while problem shows up your testing will not help
 

Capt Ken

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Jul 30, 2002
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2,269
Try squeezing the primer bulb when this happens. If it clears the problem up, then replace the lift pump.
 

Angie P

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Apr 2, 2015
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Update: Replaced high pressure fuel pump, new fuel injectors and new plugs. Running much better but still not wide open. 3 of 4 plugs look like they are firing, one looks brand new. There is fire to the coils for each plug. What could it be now? Ignition, piston ring??? Running out of ideas. It is running much better but not back to normal. Please give me some ideas
 
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