1998 90hp precision blend Yamaha leaking when shut off

Kadentheboatlover

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Sep 28, 2015
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Hey Guys,

I've got a strange problem on my hands... my engine runs perfectly, starts easily without and coaxing, ramps up, idles low. All that good stuff however... When I shut the engine off, gas leaks out and into the water. I noticed it about 2 weeks ago and have only used the engine twice since then but it has happened every time. This engine is on a commuter boat so its very important that i keep it running well also I will be escorting in the Nanaimo bathtub races so i need to fix this pretty soon races are in 2 weeks. I am great at fixing stuff but I am really lacking in the diagnosing department. If you guys need anything to aid in figuring out what the problem is like, a picture, a video or a description of something, I'm you're guy... Any ideas???
Please no suggestions of taking it to a mechanic I'm only 17 and can't afford a repair bill right now.
 

99yam40

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Sep 7, 2008
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someone will have to look to see where the fuel is leaking /coming from.

is it coming out of the carbs somewhere?
fuel pump?
or fuel lines?
fuel filter?

while running there is a suction on the lines up to the pump
when shut off that suction goes away, may let fuel leak out.
But it would alow air to get in while running
 
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Kadentheboatlover

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*update* today at 7:15 my time.

the leg was down when i got home after church. the hydraulics in the leg could be shot :( do you guys think this could be the problem ie: maybe its not gas in the water at all when i shut the engine off but hydraulic fluid.
 

robert graham

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Apr 16, 2009
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Run motor a few minutes, remove upper cowling, look to see where gas is leaking from.....maybe a gasket on a carb float chamber?
 

99yam40

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*update* today at 7:15 my time.

the leg was down when i got home after church. the hydraulics in the leg could be shot :( do you guys think this could be the problem ie: maybe its not gas in the water at all when i shut the engine off but hydraulic fluid.

You have to be kidding me,

you need to look at your motor and figure this out as we cannot from where we are
 

Kadentheboatlover

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ok I'll fire the engine up without the cowling on and try to see where the leak is coming from, thanks for your guys time i really appreciate it. I'll report in later :)
 

Kadentheboatlover

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ok... I know what the problem is. the drain plug for want of a better word for carb number 1 (going bottom to top) has its head snapped off. hence the fuel just pours out of the carb. I am pretty sure I can fix it with marine goop or a sealer of some kind, but do you guys have a better suggestion before I can never drain my number 1 carb again?

so after you're done mulling over that problem I have another. My engine keeps lowering its self over time which is a major problem for me beacuse I moor at a dock the goes dry on an 8ft tide. I'm in the mud like 1/2 of the time which is awful for the engine and the boat if the leg is down. any idea about what problem is here?

THANK YOU SOOOO MUCH!!! For everything that you guys do on this forum I'm sure you guys help guys like me every day and just want you to know how appreciated it is :)
 
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robert graham

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With the head of drain screw broken off try a small screwdriver or similar tool to remove it....then get a replacement. I wouldn't want/need to fix the carb so it can't be drained for water or debris removal in the future....most tilt/trims will leak down over time....can you just set the tilt lock on the motor?...
 

Kadentheboatlover

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Sep 28, 2015
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Ok I'll try to get the last bit of the drain screw out with my small screwdriver set I just found. However if i do get the last bit out, where in the world am I going to find that exact screw to replace it? I need to have this fixed in 11 days preferably before then (that's when the Nanaimo bathtub races are)

thanks for that helpful tip on the trim I'll put the tilt lock on from now on when I wont be using it for a couple days :)
 

robert graham

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The drain plug is a brass hex-head screw with an O-ring under the head....no need to over-tighten it, especially since the brass is softer/weaker than a steel screw....
 

Kadentheboatlover

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hey guys,

thanks for all the tips and sorry for the late reply. this all worked out great i got in a new drain screw in time and was able to escort in world championship bathtub races. I escorted tub 055 and he came in 3rd in his class. have a great day, and again thank you for all your help!
 

Kadentheboatlover

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Sep 28, 2015
Messages
33
]this is my drain screw, it has a hew head with a slot in the center of the head into which a Stanley (flat head) can be inserted. hope this helps to clear up the mystery of the Yamaha drain screw Stanley problem.
 
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