# 150 yamaha 2 Stroke



## Darrell27 (Jul 18, 2009)

Hello all,

I have a 150 HP yamaha 2 stroke 95 model that will not progress past 3000 RPMs. At first it tried to get on plane and immediately went back to running slow speed. Carbs have been removed, cleaned, and put back with new fuel lines. We have the diaphragms to change on the fuel pumps but dont know if this will do any good. Any other suggestions of what may be doing this? My thoughts were that maybe the oil reservoir is not working and the motor is going into derate.

Any help is greatly appreciated,

Thanks,

Darryl


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## DOUBLE "D" & LV (Oct 2, 2007)

Also check the throttle arm on the side of the motor. The top of that is for the timing If it is not moving at all, it is stuck and needs to be lubed. If you are saying the motor tries to go then back off, then it could be a few things. Fuel pump, thermostats, water pump are a few. If the alarm is working and not sounding, then I would be looking towards a fuel related issue (fuel pump, fuel line air leak or restriction)or timing advance issue. If it does sound, look for overheating or oil issues. One other thing comes to mind.... it is rare for a Yamaha, but the high speed side of the stator could have gone out and is limiting the rpm's. Try the simplest first, then if you think it may be an expensive item, have it checked out first. I'm sure if you wanted to have someone diagnose it, you could do the work yourself to save some that way if you get to your wits end with trying. Good luck.


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## capt wade (Oct 5, 2009)

Have you checked your main fuel tank?? I had a water problem with mine earlier this year. It would crank run fine for the first few minutes plane the boat and then not turn over 2500 to 3000 the rest of the day, turns out i had about3 to 4gals of water in the 55 gal main tank and we kept sucking up way more water than it can pass.


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## mekell (Sep 27, 2007)

To verify fuel pump problem, this MAY help. Have someonemanually pumpingthe fuel bulbs while under accelaration. If you are able to keep up with fuel demand by doing this, you have found the problem.


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## amarcafina (Aug 24, 2008)

Second on pump the bulb, sounds like pump diaphram !!


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## jman (Oct 5, 2007)

I am a friend of Darrel27 and just wanted to add that there is an arrow on his rpm gauge that is pointing towards a green circle that looks like some kind of fluid level that is almost full. There are 2 other lights that do not have arrows: starting from the left side there is a yellow circle that is almost empty (also looks like some kind of fluid level), in the middle is what looks like some kind of oil container with a drip coming out, and on the right is the green almost full fluid level (whatever this is). 

Does anybody know what this arrow indicates?

This may be where we need to be searching for the problem.

Thanks,

Josh


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## Deeplines (Sep 28, 2007)

If the green one is lit then now problem. That is the oil lights for the small tank by the engine. If your small oil tank by the motor is full then your reserve is pumping just fine. 

You are trouble shooting all the right things 1st. If I'm not mistaken there are also a sensor unit in the motor and if I remember correctly it will not let your motor go over 3K, I thought it was 2500 though, if it is bad. I think it has something to do with the temp. of the water going through the engine. Let me look at my old manual and I will post later if I find it. 

ALSO, if it is your oil reserve I have one YOU CAN HAVE. Consider it a CHRISTMAS gift. No need to spend the money on one. I think they are pretty expensive.


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## DOUBLE "D" & LV (Oct 2, 2007)

RPM reduction is set at 2000 RPM. If you have all the bars through green, your oil is full. The way the system works is: green means both tanks (engine and boat) have oil above the lower limits of each tank and oil is able to be transferred from the boat tank to the engine tank........ the yellow (no green showing) means that the boat tank is at its lower limit and oil will not automatically transfer to the engine tank. Therefore, you will run on the engine tank until it reaches its lower limit and activates the alarm and RPM reduction at which point the red on the gauge, or in that systems case, all the bars will be flashing. At this point you can manually transfer oil with the transfer switch (return to port switch)on the engine to get oil to fill the engine tank and continue running till it happens again. Your other option is to refill the boat oil tank and the system will work normally. DO NOT REMOVE THE ENGINE OIL TANK SENSOR IF YOU DO NOT KNOW ABOUT ALIGNING THE FILTER SCREEN OR MAKING SURE THAT THE SEAL IS ATTACHED PROPERLY....... IF YOU DO NOT INSTALL IT CORRECTLY, YOU CAN BLOW UP YOUR ENGINE.....Not trying to scare you, but there is no need to pull it out to fill that tank. Only pull it out if you have to. It is not a hard thing to do to be sure the filter is aligned and the seal is attached, just saying pay attention to it if you do pull it. With what you are describing as your symptoms, I do not believe you are going into RPM reduction, so I would be looking towards a fuel issue or timing issue. Before buying parts to throw at it, have it checked out. Have you done a compression check to see if you have good cylinders?


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## jman (Oct 5, 2007)

Double D,

We have not done a compression test yet but i did mention to darrel27 that it is possible that he has a hairline crack in one of the cylinders. We have the diaphragms to change out on the fuel pumps and will check to see if the line is clear to the tank and not clogged.

Thanks,

Josh


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## ucf_motorcycle (Jul 12, 2008)

First thing I always do before anything else to diagnose an engine problemis to check if it has good fuel, spark and compression.

You said the carbs are clean so just check make sure the as is fresh too and no clogged lines.

Put an inline spark tester and test make sure allcylinders are firing.

Check make sure you have even compression on all cylinders.

90% of the time one of these tests will point you in the right direction.


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