YAMAHA OUTBOARD 4a HP TROUBLE SHOOTING

[kryg]

My Yamaha 2 stroke 4 HP outboard motor suddenly stops and will not restart.
I checked fuel -OK, and changed to new Spark plug.

After a day motor restarts and motor works for about 4-5 min's then cuts out and stops suddenly, does anyone one know what causes this to happen and what should I do/look for to fix it.

Best, SV Skoiern IV, Kryg

[Seafever17]

Try running with the fuel tank lid actually opened. Sounds like it could be the vent not working and the engine can’t pull the fuel out of the tank. Runs until a vacuum is created and the dies. Slowly equalises overnight and happens again.

Just a guess….

[Seafever17]

Oh..and completely drain and clean the tank …..could be some crud getting sucked in each time

[kryg]

Originally Posted by Seafever17

Try running with the fuel tank lid actually opened. Sounds like it could be the vent not working and the engine can’t pull the fuel out of the tank. Runs until a vacuum is created and the dies. Slowly equalises overnight and happens again.

Just a guess….

It's worth a try, thanks. I once had the same problem when I was a kid with an old motorcycle.

[kryg]

Originally Posted by Seafever17

Oh..and completely drain and clean the tank …..could be some crud getting sucked in each time

Agreed, this created the problem in the last time, it was flacks of rust contaminated gas. Tank is clean also I installed an inline filter to prevent this recurring.

Thanks Just in case I will check.

[Bill O]

Are you using the top fuel tank or a remote tank?

[Tin Tin]

Contaminated Fuel, put some Seafoam in the tank

Air vent or tank hose / bulb clogged
Hose to carby has deformed or rubber has degraded (Ethanol in fuel ?)
Partially clogged jets in Carby
Float chamber float stuck/needs replacement

Choke not working properly, check connectors
Loose wires to ignition/spark etc
Kill switch faulty

[kryg]

Originally Posted by Bill O

Are you using the top fuel tank or a remote tank?

Hi Bill O:

I'm using top good fuel 94, no ethanol mix, with 2 stroke oil and OB internal tank.

Thanks Kryg

[Don C L]

Another possibility is you have a leak in the fuel line so that once the fuel gets going you are sucking air and starving the engine for fuel. I just found that on mine, the o-ring in the connector went bad and the engine would not idle. It would start with the choke on, but couldn't pull enough fuel to run at low rpm. I thought it was a clogged low speed jet in the carb, but it had been running perfectly the day before and I have an extra fuel filter. Just one other thing to check.

[kryg]

Originally Posted by Tin Tin

Contaminated Fuel, put some Seafoam in the tank

Air vent or tank hose / bulb clogged
Hose to carby has deformed or rubber has degraded (Ethanol in fuel ?)
Partially clogged jets in Carby
Float chamber float stuck/needs replacement

Choke not working properly, check connectors
Loose wires to ignition/spark etc
Kill switch faulty

Good list Tin Tin,

Thanks. Below are my comments on your list.

1. Air vent or tank hose / bulb clogged. Will check Air Vent
2. Hose to carby has deformed or rubber has degraded (Ethanol in fuel ?) Ok Checked No ethanol fuel used.
3. Partially clogged jets in Carby Need to learn how to take it apart.
4. Float chamber float stuck/needs replacement "" ""
5. Choke not working properly, check connectors Ok Checked
6. Loose wires to ignition/spark etc Ok, Checked, will recheck again
7. Kill switch faulty Seems Ok? Not sure how to recheck

Question. Does this OB have an pump to pump fuel from its internal tank or not. It seems I need to find an ID parts and repair manual for the YAMAHA 4A OB.THX KRYG

[Bill O]

Originally Posted by kryg

Hi Bill O:

I'm using top good fuel 94, no ethanol mix, with 2 stroke oil and OB internal tank.

Thanks Kryg

Ok that helps. Still sounds like it is starving for fuel. It will run on a full fuel bowl for a while, then eventually run out of fuel/stop running.

As suggested by others, loosen the cap to see if that makes any difference when running (vent is not working properly).

Didn't see a parts diagram for your motor, but had a 3.5 Tohatsu that used an internal fuel filter inside the tank at the exit port where the fuel line attached. That would get clogged and cause intermittent problems. Eventually removed it and put an inline filter which solved the issue. Check a parts diagram to see if you have this internal tank filter.

Not certain when you took the carb off last, but would pull the carb and inspect/clean fuel bowl, float needle valve and remove/clean main jet. (edit: from your response above, probably never have done this. It's fairly easy, watch a utube. Most likely this should fix it)

Let us know if anything helped fix your issue.

[Tin Tin]

Parts manual shows carby bits, example parts manual from google

https://www.marmom-marine.com/parts_...c_4acmh_04.pdf

[kryg]

Originally Posted by Tin Tin

Parts manual shows carby bits, example parts manual from google

https://www.marmom-marine.com/parts_...c_4acmh_04.pdf

Thanks TIN TIN - JUST Wonderful,

I tried to find this Parts Manual with no success.

Thank you for adding me with ideas to solve my OB mystery.
The problem would you believe was a faulty inline after market fuel filter. It was one of the white plastic filters. In cutting the housing open, I discovered that the paper element of the filter dislodged from the housing and blocked the fuel to the carby. It was installed a OB mechanic at my request. I replaced it with a transparent filter housing.

Happy Navigational experiences, Kryg SV Skoiern IV.

[kryg]

Originally Posted by kryg

My Yamaha 2 stroke 4 HP outboard motor suddenly stops and will not restart.
I checked fuel -OK, and changed to new Spark plug.

After a day motor restarts and motor works for about 4-5 min's then cuts out and stops suddenly, does anyone one know what causes this to happen and what should I do/look for to fix it.

Best, SV Skoiern IV, Kryg

Thanks everybody, you would never pick it, fault found!

Thank you all for adding me with ideas to solve my OB mystery.

The problem would you believe was a faulty inline after market fuel filter. It was one of the white plastic filters. In cutting the housing open, I discovered that the paper element of the filter dislodged from the housing and blocked the fuel to the carby. It was installed a OB mechanic at my request. I replaced it with a transparent filter housing.

Happy Navigational experiences, Kryg SV Skoiern IV.

[Don C L]

Thanks for letting us know. One more thing to add to the troubleshooting list.