1990 50 yamaha suddenly dies

hoytvectrix

hoytvectrix

Petty Officer 2nd Class
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1990 Yamaha 50ESD-JD
The engine will suddenly die right before my boat gets planed out. Makes a loud knocking noise when I re-start it, but it smooths out fairly quickly. Also doesn't idle the greatest after this happens. This happened twice in the past 3 days. The motor runs great before, and after it happens. I'm thinking its some sort of fuel issue, not quite sure though because it is sporadic.

Thanks
 
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99yam40

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Re: 1990 50 yamaha suddenly dies

loud knocking noise is never good.
Sounds like something mechanical. Motor or jet maybe locking up

Check compression to start out with.
 
hoytvectrix

hoytvectrix

Petty Officer 2nd Class
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Re: 1990 50 yamaha suddenly dies

Good call. Top 2 cylinders have 120 psi, bottom cylinder is reading a little under 60. I'm guessing its time for a rebuild.
 
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robert graham

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Re: 1990 50 yamaha suddenly dies

Maybe you can locate a used/rebuilt/remanufactured powerhead to install?....should be of interest to know exactly what caused reduction of compression in that bottom cylinder. Good Luck!
 
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99yam40

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Re: 1990 50 yamaha suddenly dies

Lean burn from plugged jets will cause piston/cylinder damage,
and so will leaking fuel pump on #3 crankcase washing oil off
 
hoytvectrix

hoytvectrix

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Re: 1990 50 yamaha suddenly dies

Is there any way to test the fuel pump for leaks? I guess I should also clean the carbs as well.
 
hoytvectrix

hoytvectrix

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Re: 1990 50 yamaha suddenly dies

I don't have time to start the rebuild right now, but I am interested in looking into what caused the problem. Would I be better off buying a new fuel pump, cleaning the carbs, or could it be an oil pump problem?
 
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