Outboard issue - looking for ideas/input

F

FootballFan

Well-Known Member
Jun 20, 2012
3,581
Florida
Boat Info
Marquis 59
Engines
MTU Series 60
Hi All,

Problem with the outboard on our dinghy.

Yamaha F50, model B, Approximately 2 years old.

Problem started with the motor shutting down at low idle. Running at higher RPM's, everything was fine. Then coming off plane and idling the engine, after a few minutes would start coughing then die.

Discovered that if I pump up the primer bulb, engine would restart immediately, run for a few minutes. Last time I had it out this week, lost prime while running at higher RPM.

Appears to me to be a fuel issue, losing prime.

What I have done so far:
  • Replaced the fuel water filter/separator (can type screw on filter).
  • Verified there is not a problem with the check valve on the line coming from the tank.
  • Replaced the filter in the screw on fuel plastic container on the back of the engine.
First thought I had this was a filter issue, but all filters have been replaced.

Problem has been across multiple fill up's of the gas tank.

Any ideas or possible directions to investigate would be appreciated.

Thanks
 
Two thoughts, you might have a high pressure filter, as Yamaha puts them in the VST (if you have that). Also check electrical conn tins. At low idle the Yamaha's will choke out due to low electrical. Yamaha have mutltiple filters after the typical screw on that you see on the side with the clear bowl.
 
Does the primer bulb collapse? Any leaks when you pump it up? There is also a seal in the quick connect where the fuel line attaches to the powerhead that can allow air to enter if damaged.
 
Is there water in the fuel tank? Did you just refill or flush it? Maybe dump the separator into a jar and see if there is still water getting in it?
 
Not that this is definitely your issue, but a common (wear item) culprit is the low pressure pump. The fact that you can pump the bulb and make everything alright also backs up this likely scenario. Especially if you can pump it and keep the engine running. The LP pump fills the VST (which contains your HP pump). The VST is like a mini, on engine, fuel tank.
 
Lazy Daze said:
Not that this is definitely your issue, but a common (wear item) culprit is the low pressure pump. The fact that you can pump the bulb and make everything alright also backs up this likely scenario. Especially if you can pump it and keep the engine running. The LP pump fills the VST (which contains your HP pump). The VST is like a mini, on engine, fuel tank.
Click to expand...
The VST also has a filter at the bottom, the mechanical LP pumps can be tested by seeing fuel level drain from primary filter. If draining, then mechanical pumps are good.
 
Sounds like the vent is closed on the fuel tank and is starving the the engine at idle. Is the fuel tank collapsing while your at full throttle?
 
Lots of good things to investigate. Thank you all.

I was at the end of my ideas and you have given me additional avenues to explore.

Thank you
 
Is the hose on the correct direction.....I got mine turned around one time not paying attention.
Arrow on bulb for fuel flow. It will run but not well.
 
I have a 2005 60hp 4 stroke yamaha with 218 hrs and have this manual somewhere in the boat and have had fuel issues with stale fuel. I got rid of all the bad fuel and changed the remote filter and cleaned out the motor filter and the motor started right up. Really need to get my boats out on the water. I'm going to see if I can download this to my desktop with the rest of my boat imfo.
 
Finally getting back to post resolution.

I went through everything I could do. No success. Sent it to a shop I trust.

The fuel tank on the AB has a pickup hose, 18 inches or so. For some reason it had curled upwards, was causing air to get into fuel system when the tank was not completely full.

Hose replace, have run for a few hours. Problem appears to be solved.
 
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Glad the boating industry is rushing to outboards for all of their simplicity and problem free operation.

It makes me wonder how many stern drive boats I could sell with empty plastic outboard cowlings attached to the stern.
 
I have boats that has a sterndrive and one with a 60hp yamaha 4 stroke, I have had more issues with the sterndrive than the outboard and the outboard has been ran in saltwater for almost 200 hrs yet no problems. If I could afford it I would convert my 24 ft weekender over and then go boating. With outboards you have very little chance of fuel explosions and are easier to maintain and if needed to replace. This is my first time with a sterndrive engine and so far I have been constantly working on it since I bought it. It is a 77 model and has issues most small and annoying but keep me out of the water. I have fixed all the large issues and replaced and upgraded most of the areas in the boat. Now it is a trim issue that worked and then not and then will go down but not up. I have taken a rest from working on it out of frustration and will get back on it when I feel like it.
 
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