old Merc 150 strait six, Losing power

K

Killshot

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May 15, 2005
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I have an old mercury 150 straight 6, I just had the carbs rebuilt and have changed the fuel filter, water pump. <br /><br />It will start Ok and once it warms up idles good. I can run it wide open for the first 5-10 minutes but then it suddenly goes from high rpms to idle rpms yet the I do not move the throttle at all.<br /><br />After this happens Its hard to get it back up to fast speed and once i do it dies again.<br /><br />almost is like it is not getting enough fuel at high speeds<br /><br />Please help any direction will be greatly appriciated<br /><br />Sean
 
L

Laddies

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Sep 10, 2004
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12,218
Re: old Merc 150 strait six, Losing power

I think the engine is starving for fuel, have someone pump the bulb to see if it's the fuel pump, if it's on a built in tank it could be the anti-syphen valve at the tank sticking
 
Clams Canino

Clams Canino

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Re: old Merc 150 strait six, Losing power

And check the venting for the tank.<br /><br />-W
 
K

Killshot

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Re: old Merc 150 strait six, Losing power

Thanks for the quick replys, How do i go about checking the anti syphon valve?
 
Clams Canino

Clams Canino

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Re: old Merc 150 strait six, Losing power

Easily check it you can not. Located at the output of the fuel tank is it. Easier to replace while in there as not.<br /><br />Easier to borrow a 6 gal "dummy can" and see if your problem leaves.<br />-W
 
C

Chris1956

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Mar 25, 2004
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28,890
Re: old Merc 150 strait six, Losing power

Killshot. I have one of those motors. The single fuel pump that I have on mine (some have two) must work at peak efficiency to keep the carbs full. Watch that your fuel line is at least 5/16" ID and that your external filters do not restrict the flow of fuel.
 
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