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Loss of RPM's at full throttle

Lucky_LeftyLucky_Lefty Posts: 89 Greenhorn
I have a 2004 Yamaha F115 4 stroke. I am having a problem with rpm's at full throttle. Yhe most I am able to achieve is 4100rpms. I did a tune a few days ago . Went out today and at first it ran fine but by end of day wide open throttle I could only go 8-10 mph ended up getting towed in off ocean. Tow driver says spun prop. At dock it will rev to 5,000 + rpms under load max is 4,000. Any suggestions.....
2004 KeyWest 1900 Sportsman Yamaha F115

Replies

  • DunkDunk Posts: 107 Officer
    Questions...

    What kind of a TUNE did you do? Then what is running fine? What RPMS and speed were you getting when it was running fine? What boat is this engine on?

    I suggest you stop revving the engine to 5K in neutral unless you want to see rods thru the block.
    Marine Surveyor
  • Lucky_LeftyLucky_Lefty Posts: 89 Greenhorn
    New plugs, Thermostat, Fuel Filter, Gas/water seperator, anodes, oil & filter. What I thought was fine was actually probably not fine. The rpms that I was getting from since I bought the boat was around 4100 rpm's. Speed was around 37 tops. The boat is a 2004 Keywest 1900 Sportsman. When I revved it up it was for a split second at the ramp in the water. I am tending to think it might be VST or plugged fuel injectors.
    2004 KeyWest 1900 Sportsman Yamaha F115
  • FLDXTFLDXT Posts: 2,521 Captain
    New plugs, Thermostat, Fuel Filter, Gas/water seperator, anodes, oil & filter. What I thought was fine was actually probably not fine. The rpms that I was getting from since I bought the boat was around 4100 rpm's. Speed was around 37 tops. The boat is a 2004 Keywest 1900 Sportsman. When I revved it up it was for a split second at the ramp in the water. I am tending to think it might be VST or plugged fuel injectors.
    Sounds like a fuel issue to me. Could be corn juiced fuel lines, filters, etc...Where you running with a full fuel tank? Could also be a cracked pick up hose in the fuel tank if the fuel level drops low enough.
  • jawzjawz Posts: 137 Officer
    New plugs, Thermostat, Fuel Filter, Gas/water seperator, anodes, oil & filter. What I thought was fine was actually probably not fine. The rpms that I was getting from since I bought the boat was around 4100 rpm's. Speed was around 37 tops. The boat is a 2004 Keywest 1900 Sportsman. When I revved it up it was for a split second at the ramp in the water. I am tending to think it might be VST or plugged fuel injectors.

    here's a great piece of advice:

    take theboat to a qualified repair facility - throwin parts at it,is going to cost you more in the long run...
  • DunkDunk Posts: 107 Officer
    New plugs, Thermostat, Fuel Filter, Gas/water seperator, anodes, oil & filter. What I thought was fine was actually probably not fine. The rpms that I was getting from since I bought the boat was around 4100 rpm's. Speed was around 37 tops. The boat is a 2004 Keywest 1900 Sportsman. When I revved it up it was for a split second at the ramp in the water. I am tending to think it might be VST or plugged fuel injectors.

    I'd ask what size prop you are running? What pitch because the speed is about right for horsepower and size boat. Either that or it's just a bad tachometer.
    Marine Surveyor
  • cookin outcookin out Posts: 239 Deckhand
    had same issue a few years back on a yam.....It could be anything but my issue was clogged injectors.....mine actually improved by getting the fuel level low and adding tripple the amount of injector cleaner and running it pretty hard......it made a huge difference but did not completely cure it.....dealer repaired injectors after that, all was well....

    good luck whatever it is.....its never easy with outboards
  • Lucky_LeftyLucky_Lefty Posts: 89 Greenhorn
    Well here is a update. Had ScottR help me with the VST replacement. I took it back out and it still would not even get on plane. I had a friend help me with the injectors. We removed them and I had them tested and rebuilt at the Fuel Injector Clinic in Hobe Sound. They called with a pre test check (240 is recommended flow cc/min) The results were Injector One = 68, Injector Two = 36, Injector Three = 216, Injector Four = 16. After cleaning all 4 Injectors they are flowing at 240. Installed them tonight as well as replaced lower unit gear lube. Will be doing a test with it tomorrow and will let you know if this fixed it. I have to believe with the plugged injectors this had a lot to do with it.
    2004 KeyWest 1900 Sportsman Yamaha F115
  • DRIFTER_016DRIFTER_016 Posts: 144 Officer
    Sounds like you should be good to go now.
    Might want to start running some form of injector cleaner with each fill up.
    Maybe some Seafoam, Mercury Quickclean or the Yamaha equivalent to prevent this from happening again.
    You should also be running a fuel stabilizer especially if you are running fuels containing ethanol.
  • Lucky_LeftyLucky_Lefty Posts: 89 Greenhorn
    Well finally got out today for a test drive. Boat runs great was able to get to 5400 rpm's with 40 gallons of gas and 2 people gas has been treated with startron and seafoam. Thanks for all the advice and tips. Once the gas is burned up it is ethnol free from here on out. Since the VSt and injectors as well as a complete tuneup the motor should be good for at least 100 hours.
    2004 KeyWest 1900 Sportsman Yamaha F115
  • DRIFTER_016DRIFTER_016 Posts: 144 Officer
    Great news Lefty!!!
    Now go catch some fish!!!!! :fishing
  • cookin outcookin out Posts: 239 Deckhand
    I would check your owners manual, my engines are 2008s and are built to run up to 10% ethanol.....regular gas is better for sure but your engines may be built to run it as well. No sense spending an extra dollar per gallon if you dont have to.....
    With that said, I run my engines at least twice per month and always add fresh fuel on EVERY trip out.
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