1999 Yamaha Vmax 150

[jackhammer]

The outboard acted up on me at Green River this weekend. It sounded funny when I started it. I floored it to get on plane and it would not get on plane. It ran like it was starving for gas. It was running very rough but would idle with no problem. I figured it may be a fouled plug, so I'm going to try that first. I have been told it could be the carbs jets stopped up. I was also told it may be a power pack. Any help would be appreciated if you can diagnose my outboard problem.

[Flatbottom Bass Assassin]

Was this the first time you ran it in a while?

[Flatbottom Bass Assassin]

Well anyhow...I had a 40HP motor that did the same thing...Would idle fine, but when wanted to take off it would run very rough. I was running on one cylinder because I had a very small hole in a diaphram in the fuel pump. Thus allowing gas to drown out one of my cylinders. Check your sprak plugs on this and it might tell you your answer(if it's same problem). You might have some very clean spark plugs and some dirty ones(clean one or ones from the gas).

[stratos294]

If it is a ox66 150 it sounds like a oxegen sensor I had to put 3 on my 2000 150, was told it was a weak point on that motor. water in the gas will knock them out. If it is the carb version sounds like a fuel pump, I had a friend with a 99 200 carberated motor and he also had a similar problem it wound up being somthing in the fuel pump.
Hope this might give you some place to start.

[mhall]

The outboard acted up on me at Green River this weekend. It sounded funny when I started it. I floored it to get on plane and it would not get on plane. It ran like it was starving for gas. It was running very rough but would idle with no problem. I figured it may be a fouled plug, so I'm going to try that first. I have been told it could be the carbs jets stopped up. I was also told it may be a power pack. Any help would be appreciated if you can diagnose my outboard problem.

My 2000 model Vmax did the same thing but cleared up after I bought some real gas with no water in it. Fuel up with fresh new tank put a little sta-bil in it and change the water seperator filter if you have one. Do all this before you go any farther and see what happens.

[Bobby Headrick]

Yes Jack check the gas and put a fuel stablizer in it as suggested above, also I have heard that the ethonol fules will make boat motors run different, anybody else heard this. They say use this new Stabil formula for this.

[jackhammer]

I'm going to try plugs, gas and stabil first. I sure hope that's the problem. Thanks for the help, I appreciate it.

[dc chopper]

A friend had this happen on his merc. It was his lower unit. He said a sensor was kicking in telling the motor not to run above idle if that makes sense. He said to check the oil in he lower unit and see if there are any metal chips. check the gas,the sensor and if thats not it you MAY be looking at a lower unit.