Yamaha Outboard Engine Trouble...

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  #1  
Old 04-17-10, 04:44 PM
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Yamaha Outboard Engine Trouble...

Hey all,

I purchased a 1984 Yamaha 8HP 8SN Outboard motor last year at the start of the boating season. It ran perfectly for the entire summer and now that it is time to pull it out for this season I have not been able to get it to stay running.

Like a dummy, I left the gas in the tank from last year (5 months old) and tried starting it. I was able to get it started several times but it sputtered and died. I am well aware of the fact that old gas gums up the carbs. Thinking that I had gummed up my carb, I took the carb out and disassembled it, cleaning all of the lines with carb cleaner, fresh gas and seafoam. I checked the diaphram and all connections and found that I was able to get the engine running by manually injecting gas into the system (bypassing the carb). This was done to make sure the problem wasn't electrical.

Next, I did tests to follow the fuel flow from gas tank to carb and found that for some very strange reason the gas was unable to enter the float bowl. I checked both the float pin and the float itself and they appear to be in working order. I ensured that all lines are clear leading to the float bowl by blowing compressed air into the lines. For some strange reason, the gas will not push the pin down and allow the gas to enter. In order to make sure that no lines were blocked, I completely removed the float and pin assembly, remounted the carb and pumped the fuel ball several times. As expected, this immediately flooded the engine since the float was no longer limiting the gas intake.

I am starting to run out of options and I am wondering if there is anything else to try. Everything appears to be clean and in excellent condition but it just doesn't seem to want to go. Any help or ideas would be greatly appreciated.

James.
 
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  #2  
Old 04-18-10, 08:19 PM
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No ideas out there? Would love to hear what a "carb guru" thinks my problem might be.
 
  #3  
Old 04-19-10, 12:45 AM
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The fuel shouldn't push the float down, it should hang down just by gravity and the fuel in the bowl should float it up to shut the fuel off when it fills the bowl. Sounds like your float isn't moving freely.
 
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Old 04-19-10, 08:25 PM
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You are correct... my wording was wrong. What I meant to say is that the float pin does not seems to be dropping far enough to allow the gas to pass through. Is it possible that there is a blockage somewhere? Does the carb have air intakes to aid in the flow of gas? I have blown out every jet and line I can see and all of them seem to be flowing freely. Also, how do I know if my pin/float is correctly setup? Thanks in advance...
 
  #5  
Old 04-23-10, 01:12 PM
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To know if your pin/float setup is correct, you need a manual with a diagram. The fuel bowl should "vent" somehow, but I'm not familiar with your particular unit. Look at the roof of the fuel bowl area and figure out which hole vents outside the carb by blowing carb cleaner spray thru it. Maybe an insect got in it and sealed it with it's cocoon. I've never had it happen to a carb, but it has happened to the little coolant outlet tube.
 
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