5 HP Yamaha won't stay running

[a64pilot]

Some engines I believe the kill switch completes the circuit, that is remove it and you will get no spark, the kill switch functions by opening the circuit, not grounding it, find out which yours is.

[deblen]

Take carb off & take it to a source of compressed air.Disassemble & blow out all passages.Blow/clean out any "white guck/corrosion" from bottom of bowl.
Add an ounce of methyl hydrate/gas line antifreeze to every tank of gas.It will disperse the water in your fuel & allow it to pass thru carb.O/B s operate in a humid environment,& water vapor from the air WILL accumulate in ur tank.Eventually,it WILL get into carb-hence the white powder/gel guck in bowl.Don't ever use Ethyl-gas.The ethyl alky WILL draw water out of air & gum up carb,plus it separates into alky & low octane gas quite fast.
Most useless fuel idea ever invented.Use good cropland to grow fuel additive,that creates 10x the energy/pollution to create.End of sermon.

[JPA Cate]

landonshaw,

Since you said you have no spark, had you tried substituting a new, properly gapped plug, to see if it DID spark?

Yes, you can use the bulb in the fuel line, but if everything's working right and the pickup is deep enough, you shouldn't have to.

Ann

[dlymn]

I had this problem on a small motor recently. It turned out to be a crack in the little plastic priming bulb. It was small denough to let me pump fuel up but it then allowed air to get into the system and stop flow. Eventually, after much pumping, the bulb just fell apart.

[landonshaw]

Went to the dinghy tonight. Disconnected the kill switch, pulled the spark plug and cleaned it. The spark plug was only a week old. Pumped the gas bulb and started the engine. It started in two pulls. Let it run at fast idle for maybe 5 minutes. It then stopped on its own. The bulb was not firm with fuel so pumped it. Restarted the engine and ran for 5 minutes and the bulb stayed full of fuel. Tomorrow I will try running the dinghy around the bay. Did not want to go out tonight in the dark. The kill switch is still disconnected. I will let you know tomorrow on the outcome. Maybe.....


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[MBWhite]

Originally Posted by 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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1) What year and model is your motor?

2) There seems to be some confusion as to whether the issue is fuel related or ignition related. I do not recommend this as a standard procedure with 2 stroke engines but done sparingly it is fine and provides invaluable information- Give the carburetor a 1/2 second shot of starting fluid and see if the engine fires off. If it does then you know you have a fuel problem, and if it does not then you have an ignition problem. Do not use any more ether as you run the risk of washing what little oil is left on the bearings off if it is a 2 stroke motor (4 stoke motors do not need this precaution). However, this will point you in the direction you need to look.

[noelex 77]

I would be surprised if its not the carburettor, but someone else has mentioned the saftey kill switch which can be a source of problems on Yanmar outboards.

The switch works by using a plastic spacer to pull the button out. If the internal contacts of the switch become degraded the switch can become intermittent. A simple test is to pull the switch out more with your fingers while trying to start the motor. The extra pressure creates a better contact. If this works you have diagnosed the problem.

[landonshaw]

So disconnected the kill switch and the motor still stops after a few minutes. I have the motor home and will take it apart again, clean the needle and make sure the float is working properly. Take out the jets and clean. I have another old 5 ho so will put that pump on the one jam trying to fix. The pump bulb seems to be soft when it has stopped so am thinking it might be the fuel pump, diaphragms. Then try it again.


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[landonshaw]

I will also put a different engine on the dinghy and use the same external gas tank and hose with the bulb pump to be sure that is not the problem. Someone earlier mentioned they had a small hole in the pump and it would let in air. I will eliminate this possibility with the replacement engine.


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[dlymn]

I'll go out on a Lymn and still plug for air getting into the fuel line and probably from the priming bulb. These little fellas are plastic and subject to the vicissitudes of constant exposure to the elements as well as the corrosive effects of dodgy fuel. They will go hard over time, especially if they are sitting around on the transom month after month.

When you pump, the crack is sealed enough to allow the fuel to be pumped but when you stop pumping, the crack is not under compression and the system suck air in.
The trouble with pulling these carbies apart is that they are somewhat fussy and it is really difficult to get them perfectly reassembled.
The most likely cause of the problem might be water and crap in your fuel and that's not hard to get if the fuel tank lid is not tightened down every time after use. Once you get water into the carby it's useless. No amount of cleaning and corrosion removal will restore the carby to new.
You can buy complete carbies ($$$$$). I think they're made in China and Yamaha might pay < $20 for them. Google Aliexpress and search for carburetor yamaha

[Lodesman]

See post #17. Sounds like you have some water in your fuel tank. Drain the tank and refill through a baha filter, or tilt it up on one corner, then siphon a little right out of the bottom of the corner into a glass jar. If you see water, siphon until no more water; clean and reassemble carb; and stay away from ethanol mixes.

[landonshaw]

Changed the pump bulb and hose. Engine started then died, started it again and it ran for about 5 minutes. Thought all was fixed. Then it died again and the bulb was not hard. Now I will go and buy the parts for the fuel pump and replace them. I had the kill switch totally disconnected the first time when it died. Hooked it back up and the engine reacted the same. Both times I had no trouble starting the engine so it seems like the electrical system is ok. I will clean the carborator when I change the pump parts. Any other suggestions?


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[sparrowhawk1]

're read my posts

[landonshaw]

Sparrowhawk1
I checked the plug and it looks good. Dry, new plug, just used in the past test.
I will check the bowl this weekend. My thought is that gas is not being drawn up from the tank, in which case the engine runs until it has no fuel to refill the bowl to feed the carborator. I would expect to find fuel in the bowl, but not full.
Does the fuel pump draw gas from the tank and with that pressure feed it to the carborator?
Each time the engine has stopped, the bulb in the fuel line from the tank has been soft.
When I cleaned the carborator the last time, a few days ago, the float and needle both seemed to be in good working order, not stuck or out of shape.
The engine is a 5 hp, 2008 or so vintage, Yamaha

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[IslandHopper]

Originally Posted by noelex 77

I would be surprised if its not the carburettor, but someone else has mentioned the saftey kill switch which can be a source of problems on Yanmar outboards.

Have not seen one of them for years, never seen one with a carby though...