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1999 150 hp 2 stroke

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rjw4259

Contributing Member
I have a 2 stroke Yamaha 150 hp that will not stay on plane it begins to sputter then gradually loses rpm and goes off plane. Acts like its not getting ample fuel. I also noticed that the fuel bulb is sucked flat, have to pull it out of the fuel line to get it to inflate, also cannot get a firm fuel bulb, stays spongy. Any help appreciated, thanks.
Bob:(:(:(:(
 
The collapsed bulb is usually caused by either the vent to your fuel tank being clogged (critters love to nest in there) or a clogged pickup in the fuel tank. However, you said that you can't get a firm bulb, so that tells me that the internal check valve in the primer bulb may have failed. Replace it and also check your vent and pick up in the tank.
 
Hi CHawk,
Thanks for info, bought a new primer bulb will install that asap. I tried running the motor with the gas fill cap opened, with same result. I checked with my service man and last year around August I had this same problem, according to his maintenance record the anti-siphon valve in the tank was replaced and the motor ran fine after repair. Is that valve something that can be expected to fail that quickly? He put a new water fuel separator cartridge at that time. I filled the tank completely before docking the boat this season, didn't see the problem until the tank was showing around half full mark, not sure what relevance that has but I plan to fill the tank when i replace the bulb just to see if it has any good effect. I will be back to let you know how it goes after replacing the primer bulb. Thanks again.
 
Last edited:
Original post :
I have a 1999 2 stroke Yamaha 150 hp that will not stay on plane it begins to sputter then gradually loses rpm and goes off plane. Acts like its not getting ample fuel. I also noticed that the fuel bulb is sucked flat, have to pull it out of the fuel line to get it to inflate, also cannot get a firm fuel bulb, stays spongy. Had the anti-siphon valve in the boat tank replaced last fall for the same problem. I started out the season with a full fuel tank, did not have any problem with the engine until my tank reached a little less than half full, not sure if that is related to the issue but thought I should throw that in too. Any help appreciated, thanks
 
The anti-siphon valve should not fail that quickly UNLESS you have a bunch of gunk in your fuel tank.

If you trailer the boat, jack up the tongue, then jack up one side of the axle to give it a tilt. Remove one of the access plates to the tank - either for the pick up tube, or for the fuel gauge sender. Let it settle for a while. Then snake a siphon tube to the lowest part of the tank and draw out a few pints of fuel into a clear jar. Let it settle and see what you have. If it's all water, you know what the problem is and the tank will need to be drained.

I do this about every three years or so as SOP. I use an after-market 12 V fuel pump to do the job.
 
rjw4259 said:
Original post :
I have a 1999 2 stroke Yamaha 150 hp that will not stay on plane it begins to sputter then gradually loses rpm and goes off plane. Acts like its not getting ample fuel. I also noticed that the fuel bulb is sucked flat, have to pull it out of the fuel line to get it to inflate, also cannot get a firm fuel bulb, stays spongy. Had the anti-siphon valve in the boat tank replaced last fall for the same problem. I started out the season with a full fuel tank, did not have any problem with the engine until my tank reached a little less than half full, not sure if that is related to the issue but thought I should throw that in too. Any help appreciated, thanks
Click to expand...
The primer bulb sucks flat because of a fuel restriction somewere from the primer bulb to the end of withdrawal tube in the tank.
 
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