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Author Topic:   Fuel starvation 1986 150 hp Yamaha
Abalonehunter posted 01-20-2004 03:38 PM ET (US)   Profile for Abalonehunter   Send Email to Abalonehunter  
My brother has been having what appears to be a fuel starvation problem with his 1986 150 hp Yamaha. The scenario is basically at almost any rpm upon no real notice the motor dies or just about dies. This past weekend the occurrence happened at about 2800 rpm, 3200 rpm, and several times at 4000 plus rpm. When you reach down to check the primer bulb it appears empty and pumping it back up seems to work but then you never know when it will happen again. We routed the bulb from the engine side of the fuel/water separator (fws) to just above the fuel tank and before the fws and thought that it actually made a difference but all of a sudden it happened again. In the past he’s tried a separate 6 gallon tank to see if it may be a “tank” problem but it happened with this tank as well. A friend of ours who was out with us has a low pressure 12v fuel pump that he thinks would do the trick were just not sure and haven’t got it yet to try out. What we’d like to really find out is why it’s happening. Could air be getting into the system somewhere and causing the problem? Could it be one of the fuel pumps on the motor? Any and most suggestions appreciated.



slightseas2 posted 01-20-2004 06:26 PM ET (US)     Profile for slightseas2  Send Email to slightseas2     
Not sure about the fuel deal, but my 1984 150 Yamaha was acting slugish 2 years ago. I had the carbs rebuilt two years straight with no better performance. I even thought the boat had taken on water/weight and was just heavier. Finally a mechanic at a local shop replaced the powerpack (the box that tells which cylinder to fire when. Also replaced stater. Heck-now it jumps out o the water like her old self!! Hopes this proves useful.
Buzzorouter posted 01-20-2004 08:48 PM ET (US)     Profile for Buzzorouter  Send Email to Buzzorouter     
The fuel pump would be easy enough to try- How is the filter? Fuel screens?
Abalonehunter posted 01-20-2004 11:19 PM ET (US)     Profile for Abalonehunter  Send Email to Abalonehunter     
Thanks for the replys. Filters have been replaced and double checked, all are good.
DJS posted 01-21-2004 08:15 AM ET (US)     Profile for DJS  Send Email to DJS     
Have you tried replacing the primer bulb?
Tom2697 posted 01-21-2004 09:41 AM ET (US)     Profile for Tom2697  Send Email to Tom2697     
It sounds like your fuel pump is weak or your primer bulb is malfuctioning. As DJS stated, change the primer bulb and see if that helps. Otherwise, try the 12v pump. If changing the pump works, you most likely need a new fuel pump or you might be able to rebuild it. It even could be that your pump has and internal filter that just needs to be cleaned.
Eagleman posted 01-21-2004 11:17 AM ET (US)     Profile for Eagleman  Send Email to Eagleman     
I'd replace the primer bulb with an OEM new unit immediately. I've had this happen on two different outboards that I've owned. The problem was the check valve inside the primer bulb had gotten fouled over the years, they looked good on the outside. I even have had new aftermarket primer bulbs fail out of the box, go OEM this could solve your problems. Good Luck
Abalonehunter posted 01-22-2004 02:33 PM ET (US)     Profile for Abalonehunter  Send Email to Abalonehunter     
Thanks everyone we think we've found the problem to be a air leak at the tank connection but if that's not it then we'll go with all the above. Thanks again.


kingfish posted 01-22-2004 02:57 PM ET (US)     Profile for kingfish  Send Email to kingfish     
We had a problem with sudden loss of power, particularly at mid to high speed, on our new 2001 Yamaha 225 OX66 (fuel injected), and tracked it down to one or both of two things (I fixed them both at the same time, so I am not sure to what degree either one was specifically the problem).

1. I found some loose fuel line connections where a marina had plumbed in the fuel line for our kicker from a "T" in the main motor fuel line. I removed that whole contraption and installed new fuel line in one piece from the cannister filter to the main motor, and used two plastic ratchet clamps at each connection. See #2 below...

2. The configuration described above allowed the high pressure fuel pump in the fuel injected 225 to pull air back through the carburetor in the 4-S kicker, so I plumbed a single piece fuel line from the second port on the cannister filter straight to the kicker with a petcock in the line right at the filter so I can separate the two fuel systems by closing the petcock to the kicker when the main motor is running. Double plastic ratchet clamps at each connection...

I believe that the loose connections were the primary cause of the sudden power losses.

Sal DiMercurio posted 01-22-2004 05:15 PM ET (US)     Profile for Sal DiMercurio  Send Email to Sal DiMercurio     
The way to check if the engine is sucking air is, put a clear plastic fuel line from the fuel pump to the varbs & run the engine [ on the water ] wide open while someone watches that clear line.
You wont notice bubbles in the fuel line untill the engine is at or near wot.
If any bubbles are in that line, your sucking air.
vdbgroup posted 01-23-2004 12:11 AM ET (US)     Profile for vdbgroup  Send Email to vdbgroup     
Fuel Pumps on older carbed oil-inj Yamaha's should be replaced every 3-5 years. The pumps diaphragms become weakened over time. Failure to pump proper fuel/oil mixture can result in engine damage. Consult a mechanic. 2 Fuel pumps are about $70.00. Labor is about one hour. You can do it yourself, but be careful that gaskets seat correcly.

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