Yamaha 30HP 2-stroke with only run with choke

[Yamaha89]

Hi everyone, hope you can help with this strange problem...

I have a 30hp Yamaha 2-stroke outboard with 3 carbs that seems to only run with the choke on and revs high when I do put the choke on. I replaced the fuel lines and I can see there is fuel in the fuel filter bulb on the motor. I took apart all 3 carbs and cleaned them but the problem persists. I have also tried putting fresh fuel and used spray carb cleaner.

Also, this may be related, when I pull the motor up and leave it in this position, I noticed there seems to be some oil residue on the inside of the carburetor cover.

Thanks for your help!

 

[schematic]

Re: Yamaha 30HP 2-stroke with only run with choke

1.have you tried assisting the fuel pump with the primer bulb while running?

 

[Yamaha89]

Re: Yamaha 30HP 2-stroke with only run with choke

1.have you tried assisting the fuel pump with the primer bulb while running?

Hi, thanks for your response.

To answer your question, yes I have tried pumping the bulb while running but the bulb is acting very strange. Sometimes the filter will fill with fuel when I pump the bulb and sometimes it will not... It almost seems as if air is pumping instead of fuel some of the time... When the motor is running the filter bulb runs almost dry.

Because of this strange behavior I replaced all of the fuel lines yesterday and it is still acting the same... Do you have a suggestion what to troubleshoot next? Perhaps replace the bulb, or maybe the linkage at the gas tank?

Not entirely sure what to try next.

Thanks!

 

[Toddboat]

Re: Yamaha 30HP 2-stroke with only run with choke

Things to try...
1.) Open gas cap to make sure gas line is vented. Why? an unvented fuel line could prevent fuel from getting to the primer bulb if a vacuum has formed inside the fuel tank. Venting the tank allows fuel to flow freely.
2.) Make sure when you increase the throttle, all three butterfly valves that allow air into the carbs are opening fully.
Why? If a motor runs well only with choke on, it is running off of a rich mixture with little air. The only difference between choke on and choke off is the amount of air. If a butterfly valve isn't opening, this could starve the carbs of air and explain why it only runs with the choke on.
3.) You may still have dirty carbs, the float may be sticking to the bottom of the bowl. People neglect to clean this because they only focus on cleaning the jets. This is where gas sits and gums up during storage. If the primer bulb squeezes forever without getting hard sometimes, this could be the cause. If the float gets stuck to the bottom of the bowl, the float never rises to close the needle valve. When you pump the bulb, the engine just floods. A flooded engine could drip its excess fuel and oil when tilted. I think this is the most likely problem you have because it covers the primer bulb issues, the inconsistent running issues and the residue issues. It is hard to explain all three otherwise, unless they are unrelated issues.
4.) Bypass the fuel/water separator so that you know you're getting fresh fuel into the engine. The fuel/water separator holds a lot of fuel itself. If you hook up a new fuel source to the boat, it would still take quite a while to get the new fuel into the engine if you have to use up what's in the fuel/water separator first. If you don't want to bypass it, at least dump out its contents and fill it with fresh fuel.
5.) Lastly, it could be a faulty fuel pump, but this is unlikely if it doesn't run while priming the bulb because priming the bulb rules out fuel pump issues. You may also want to check the fuel filter which is inside the motor near the bottom carb.
Keep us posted!

 

[99yam40]

Re: Yamaha 30HP 2-stroke with only run with choke

if you have to choke it to make it run it is running too lean on fuel and the choke richens it.
Pull, take completely apart, and clean carbs better, maybe an ultrasonic bath would be good.
Make sure to follow the link and sync steps in service manual after reinstalling every time, to make sure all is in sync and adjusted properly

 

[Yamaha89]

Re: Yamaha 30HP 2-stroke with only run with choke

Thanks so much for your responses. I will try to troubleshoot all that you listed today and will get back to you!

I also noticed this morning that there was a couple drips of oil below the motor today, if that could mean anything?

Once again I appreciate your responses and will try them out and get back to you!

 

[Yamaha89]

Re: Yamaha 30HP 2-stroke with only run with choke

Things to try...
1.) Open gas cap to make sure gas line is vented. Why? an unvented fuel line could prevent fuel from getting to the primer bulb if a vacuum has formed inside the fuel tank. Venting the tank allows fuel to flow freely.
2.) Make sure when you increase the throttle, all three butterfly valves that allow air into the carbs are opening fully.
Why? If a motor runs well only with choke on, it is running off of a rich mixture with little air. The only difference between choke on and choke off is the amount of air. If a butterfly valve isn't opening, this could starve the carbs of air and explain why it only runs with the choke on.
3.) You may still have dirty carbs, the float may be sticking to the bottom of the bowl. People neglect to clean this because they only focus on cleaning the jets. This is where gas sits and gums up during storage. If the primer bulb squeezes forever without getting hard sometimes, this could be the cause. If the float gets stuck to the bottom of the bowl, the float never rises to close the needle valve. When you pump the bulb, the engine just floods. A flooded engine could drip its excess fuel and oil when tilted. I think this is the most likely problem you have because it covers the primer bulb issues, the inconsistent running issues and the residue issues. It is hard to explain all three otherwise, unless they are unrelated issues.
4.) Bypass the fuel/water separator so that you know you're getting fresh fuel into the engine. The fuel/water separator holds a lot of fuel itself. If you hook up a new fuel source to the boat, it would still take quite a while to get the new fuel into the engine if you have to use up what's in the fuel/water separator first. If you don't want to bypass it, at least dump out its contents and fill it with fresh fuel.
5.) Lastly, it could be a faulty fuel pump, but this is unlikely if it doesn't run while priming the bulb because priming the bulb rules out fuel pump issues. You may also want to check the fuel filter which is inside the motor near the bottom carb.
Keep us posted!

Hi thanks for these many options. I am planning on disassembling the carbs again and going try to clean them again but before I did, I realized something that may be strange behavior for my filter bulb before the engine. I fill the filter area by pumping the bulb but then while it is running the filter area slowly empties all of its gas, and I also noticed bubbles in the filter area forming as the engine is running. Is this normal behavior?

Thanks again for your help.

 

[fritzalouie]

Re: Yamaha 30HP 2-stroke with only run with choke

1have you checked to see if all three cylinders firing.I just did the whole fuel/carb thing only to find my50 1989 Yamaha is only firing on one.