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Old 28-11-2012, 20:37   #1
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15 yamaha 2 stroke outboard

My outboard starts to miss and will die after aprox 5 min of full speed running I have taken the carb off 3 times and all seems ok squeezing the tank ball helps slightly the filter is clean any other ideas??? could it be the fuel pump diaprahm??
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Old 28-11-2012, 20:39   #2
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Re: 15 yamaha 2 stroke outboard

Check your fuel tank vent. I sounds like you are pulling a vacuum in your fuel tank. If there is a screen on the end of your pickup tube that might be clogged as well.
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Old 28-11-2012, 20:47   #3
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Re: 15 yamaha 2 stroke outboard

checked that all is clear if I diconect the fuel filter and pump the ball full flow
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Old 29-11-2012, 04:12   #4
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Check for small pinhole in the gas line near the Carb.
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Old 29-11-2012, 05:29   #5
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Re: 15 yamaha 2 stroke outboard

Did you just disassemble the carb or did you clean it? The smallest amount of residue can create a problem. By running for 5 minutes then dying, what gets it going again? Opening the fuel tank, just sitting, or do you have to row back then dissemble again? It does sound like a venting problem, or possibly a defective hose or bulb.
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Old 29-11-2012, 09:29   #6
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Re: 15 yamaha 2 stroke outboard

I completly diassembled and took out all the metering jets etc. the tank vent is open it is the same with the top off, the filter bowl stays full all the time if I just wait a couple of seconds and start up it will go again but not as far I just changed spark plugs and put new ones in am going to see if one of them is faulty
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Old 29-11-2012, 09:36   #7
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Re: 15 yamaha 2 stroke outboard

My Johnson 15 2 Cycle had the same problem. I ordered a fuel pump rebuild kit. Presto-chango engine runs great now. Upon inspection the diaphrams in the pump had lost thier pliabilty. Cost me about $14 and a hours time.
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Old 29-11-2012, 09:50   #8
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Re: 15 yamaha 2 stroke outboard

My 15hp Yamaha did that after years of heavy use, does your's rattle a little or vibrate in an unusual manner? I had to replace the main bearings. It was a fairly easy job but I had the help of an experienced OB mechanic. Hopefully not your problem.
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Old 29-11-2012, 10:49   #9
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Re: 15 yamaha 2 stroke outboard

Can you borrow another hose or hose and tank combo and try that to eliminate it being either if those. Then I would get a carb rebuild kit and a can of carb cleaner and do a complete carb job. Clean all the passages, spray into the needle valves, and just spray everything you can, then rebuild. As you have seen, they are simple carbs, be happy you have a 2 stroke, much easier to work on, in my opinion.
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Old 29-11-2012, 20:15   #10
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Re: 15 yamaha 2 stroke outboard

Some possibilities:

- Air getting into the fuel line. (Try borrowing a friends' hose. Check for pinholes, loose clamps / gaskets, etc. in all suction lines.)

- Weak fuel pump. (If aggressive primer-bulb action keeps it running when it starts to miss, the fuel pump is a prime suspect.)

- Ignition misfire. (CDI modules tend to fail as sudden-death, rather than as gradual / intermittent deterioration, but it's possible that something's misfiring when it gets hot. Check that the plug wires are making good contact and aren't coming loose or deteriorating.)

- Crud in the carb. (They do like periodic cleaning. Which reminds me, I should do mine this winter...)
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