5 HP Yamaha won't stay running

[landonshaw]

I have had a problem on my Yamaha 5 hp outboard. I will start it and it runs for awhile then cuts out. I pump the bulb from the outside gas tank, start it then nothing. I can try and try, will not start again

I have replaced spark plug, fuel filter, one of the fuel lines in the engine, pulled and cleaned the Jets and needle. Sprayed the carb with cleaner.

Two things that I am thinking. One that gas is not being pumped to the carborator. If so, then wouldn't me pumping the external bulb between the gas tank and engine alway me to start the engine again at least until the float chamber has been emptied of gas?

Second, I am not getting a spark to the plug. Had can I test this? I would think it would be easy.

If it is not getting a spark, possible my red key that goes under the cutoff is worn down, or maybe a malfunction in the cut off??

These are theories, any suggestions from people with mechanical experience?

Thanks, it has been frustrating.


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[cal33]

4stroke or 2 stroke?

To test for spark, pull the plug out and place in the boot and ground it to the engine, furthest away from the cylinder head as possible. Pull, you should be able to see it arch.

You can also look to see if the plug looks wet, or dry. If it's dry you probably have spark and no fuel.

If it's wet, you probably have the wrong fuel or no spark.

Cheers.

[landonshaw]

2 stroke


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[noelex 77]

I would clean the carburettor again. The jets and the float bowl needle are so small they regularly clog and your symptoms fit in with this problem.

I have the 4hp, but just cleaned the carb on friends 5hp which was identical.

I have done it so often I can now do this without dropping anything in the water.

[landonshaw]

I know that feeling. Tried so hard once to not loose anything. Took it off and placed it ins a box in the dinghy. Somehow the float and needle never made it to the box.

I'm going to test the plug tonight and change starter keys.

[a64pilot]

More times than I can count I've fouled a two stroke plug, cheap as they are just replace it, but easiest way to check for spark is remove the plug put it in the wire and lay it on the engine and pull the starter, that was your not having to pull against compression and knocking everything around.

But yes if your pump is bad you can start it and keep it running with the squeeze bulb

[landonshaw]

good point. Just replaced the plug last week, but as you said, being cheap it is easy to replace again then I know it is not a fouled plug. Trying to eliminate easy stuff before I start into more expensive items. Thanks

[cal33]

I would strongly recommend looking at the plug very carefully to determine the issue, ie, wet or dry. Also, a plug may fire during a test but not fire under compression. What year is the motor?

[a64pilot]

Originally Posted by cal33

. Also, a plug may fire during a test but not fire under compression. What year is the motor?

That has caused me an inordinate amount of grief in times past when as kid I used to race Hare Scrambles, I just knew it couldn't be the plug, it fired when removed.

[sparrowhawk1]

I agree with checking the plug its condition can tell you a lot about how the engines running. After the engine stalls remove the drain plug at the bottom the carb and see if a bowls worth of fuel comes out.

[Phantoms]

Is your tank vented? Have you tried opening it to see it there's a vacuum built up in it?

[Greatketch33]

Originally Posted by Phantoms

Is your tank vented? Have you tried opening it to see it there's a vacuum built up in it?

Take the float bowl cover off to determine if the float moves freely.

[landonshaw]

Tank is vented. I thought that have been a problem earlier but opening the tank did not solve the problem.


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[landonshaw]

When I cleaned the needle I did not notice any problem. I did not look directly if it was not moving but it did not seem to be any different than prior carborator cleaning times. I am going to test the electric system to see if I get a spark. I will also disconnect the kill switch to see if it is malfunctioning. If that turns up nothing, probably take carborator off again, clean and check the float.


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[sparrowhawk1]

If there's a bowl full of fuel after it stalls then it's not the needle,fuel pump, hoses or tank vent

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