06 Yamaha 150 2-stroke Bogging Down in Steps

AURanger07

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Jul 6, 2012
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I have a 2006 Yamaha 150 2-stroke that is bogging down in steps. It will take off at 4000 rpm's but before it planes out it will drop to 3000 rpm's then about 3 seconds later drop to 2500 rpm's and 3 seconds later down to 2000 rpm's. I am holding the throttle steady the entire time. Once it hits 2000 rpm's I can hold the throttle steady and it will jump back and forth between 1500 and 2000 rpm's. The boat was running fine all day and started doing this after i ran over another boats wake (Nothing that i haven't done before). The water pump is running fine and the engine is not over heating. I checked the fuel filter on the engine and found nothing that would be stopping flow to the carbs. I put brand new spark plugs in it about 3 months ago so i don't think that is my problem. Help??
 

99yam40

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Re: 06 Yamaha 150 2-stroke Bogging Down in Steps

monitor the fuel pressures to see where the restrictions are,
might have trash in VST and screens/filters need cleaning/replaced
 

AURanger07

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Re: 06 Yamaha 150 2-stroke Bogging Down in Steps

The VST filter is in the small yellowish plastic cup on the side of the engine right before the fuel pumps right? Sorry this is my first boat.
 

99yam40

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Re: 06 Yamaha 150 2-stroke Bogging Down in Steps

VST is the vapor separating tank, that is where the electric fuel pump resides.

Pick up a Yamaha service manual and read up if you plan on working on this motor yourself or take to a trained Yamaha tech that has the equipment to test and the knowledge to test
 

AURanger07

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Re: 06 Yamaha 150 2-stroke Bogging Down in Steps

Well I ended up removing all the hosing from the gas tank to the fuel pumps to check for any blockages since I have been told that the ethanol can crud up in the lines. I didn't find anything blocking the lines but what i did find was when i took the hose off the inlet of the bottom fuel pump, gas poured out. I then re-attached all my hoses and removed the outlet to the fuel pumps and replaced it with clear tubing into a bucket. When i primed my fuel lines, fuel went through the fuel pumps meaning i had a busted diaphram in both pumps. I was curious though because my motor would idle fine so both pumps couldn't be messed up. I then turned the motor over and found that the top fuel pump was pumping but not the bottom but the top fuel pump is on its last limb. I have ordered two new fuel pumps to replace these and plan on rebuilding these two pumps as back-ups since the kit is fairly cheap (even though i do not plan on needing them for a long time).

Would a problem in the VST filter cause the fuel pumps to go out or should i have no worries when i replace the pumps?? Also i will order one of those books since i have one for all my other vehicles.
 

99yam40

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Re: 06 Yamaha 150 2-stroke Bogging Down in Steps

Fuel pumps have check valves in then to allow fuel to flow through them just in one direction.
By pumping primer bulb the fuel is suppose to flow into the VST so the electric pump has fuel to pump and run the motor.
There is a good chance that one or both pumps have a problem but your test would not show it.
You would need to unbolt the pumps from motor to see if pulse port was leaking fuel.

Like I said service manual is a must
 
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