Mistakenly ran old fuel in Nissan 5hp outboard

[bikerider]

I mistakenly ran some old fuel in my Nissan 5hp four stroke. I am fairly mechanically inclined and am wondering if I can clean the carb myself? I'm also wondering if I will need to clean the fuel pump as well?

 

[pvanv]

Just flush it all out with fresh gas. Use the drain plug in the carb. Then prime, drain, prime, drain a few times.

 

[km1125]

I agree with Paul. Unless it was old gas that was filled with dirt where you might also need to change or backflush the filter.

 

[bikerider]

I will give that a try. The gas didn't look terrible as it passed through the inline filter in the line coming from the tank. I just left in it there a bit too long I think.

 

[bikerider]

I took the boat for a test run at the lake yesterday. The motor started very easily and ran great through the whole rpm range until about 15 minutes into the run. I was cruising at half throttle and suddenly it bogged down and died. I could get it to restart with the choke out and by pumping the primer ball. It seemed like the motor was starving for fuel when it bogged and died. Once it was running again it seemed to be fine. Any ideas as to what could be the issue? Fuel pump going bad?

 

[km1125]

I'd check for air leaks in the fuel hoses all the way back to the tank. Also make sure the dip tube inside the tank is not loose.

I'm assuming you already made sure that the vent on the tank was open and not causing an issue?

Also, on the fuel pump on these you can take them apart and clean them out and flip over the "valves" to get a fresh sealing surface. That may not be your issue at all, but something to do periodically to make sure it continues to run good.

 

[bikerider]

I'd check for air leaks in the fuel hoses all the way back to the tank. Also make sure the dip tube inside the tank is not loose.

I'm assuming you already made sure that the vent on the tank was open and not causing an issue?

Also, on the fuel pump on these you can take them apart and clean them out and flip over the "valves" to get a fresh sealing surface. That may not be your issue at all, but something to do periodically to make sure it continues to run good.

I checked the fuel lines running from the tank to the motor connection to inside the case all the way to the carb and I can't see any cracks or places where air would leak from. There's an inline fuel filter between the external tank connection and fuel pump that I am going to replace. The pickup in the fuel tank seems fine. I took the fuel pump off and took it apart. It looks really good inside but I'm not sure what you mean by valves? I will post of picture of the inside of the fuel pump.

It may be worth mentioning that I have an inline fuel filter in between the primer ball and the connection for the outboard and the Nissan engine has an inline fuel filter between the external fuel connection and fuel pump. Do you think this could cause the issue I'm having or any other issues, the fuel pump having to pull fuel through two inline fuel filters?

 

[bikerider]

Here is a picture of the inside of the fuel pump. Is the valve you mentioned the white circle?

 

[pvanv]

The check valves are #27 and 28 in this drawing:

 

[km1125]

Yes, the parts that Paul is pointing out. You can take that white plastic out with those two screws, then clean the parts underneath and flip them over.

I don't think the two filters in line would cause an issue unless one or both are plugged or either one has leaks that are allowing air to get in.

One way to test the system for air leaks is to run with the tank vent CLOSED for a bit. If you see the tank sides sucking in, then open the vent and if you hear the hiss of air getting in you know the system is pretty well sealed. If that doesn't happen you're getting air in somewhere and you just need to figure out where.

 

[bikerider]

Thank you for the diagram. That's very helpful. I will take the fuel pump apart and flip the plates over. I did replace the inline fuel filter under the cowl of the motor just because the motor is 15 years old and I don't know when or if it had ever been changed. I will try running the motor with the fuel tank vent closed and see what happens and go from there. I think it's worth mentioning that with the vent open on the fuel tank, the inline fuel filter outside the motor (in the line going from tank to fuel connection) (pictured) would fill up and drain what seemed like randomly throughout the day, while the boat was sitting on the trailer not running. I would walk past it and it would be empty and walk by several hours later and the filter would be full. Is this normal? I don't have anything to compare it against and am curious.

 

[km1125]

With that filter emptying and filling, it's draining gas back out of the engine. That really shouldn't happen but could if there is an air leak or if the check valves in the fuel pump are not sealing.

 

[bikerider]

I'm hoping the problem is the check valves in the fuel pump. I will post my findings after I turn them over and test run the motor.

 

[km1125]

Another test you can do to check for leaks: Disconnect the fuel hose from the engine. Close the tank vent. Put some weight on the tank (lean on it with some force) and see if you can hear any air coming out or going in. Not a perfect test, but I've found leaking vent valves that way.

 

[bikerider]

I am focusing on the fuel pump right now and if that does not solve my issues I will start looking for air leaks in the fuel system. I took the fuel pump apart and flipped over the two plates as suggested. I ran the motor on the trailer for 30 minutes at half throttle (the same throttle position as when the motor cut out while at the lake) with no problems and 15 minutes at idle with no issues. The motor started up after hot pretty easily. I am going to test run it at the lake before I call it fixed but it is looking promising.

 

[bikerider]

I took the boat to the lake yesterday and used the gas motor to get from the ramp to my fishing spot and used it to troll at idle speed for quite a while. There were several times that I shut the motor off while fishing near the shore and restarted it when I wanted to move to a different place. All in all the motor did really well. It started easily and didn't cut out once. The only minor issue I experience with it was it seemed to load up after trolling at idle for a long while but I'm assuming that's to be expected. I noticed that after I turned the plates in the fuel pump over I was no longer getting the inline fuel filter randomly filling and draining. I think the issue with it is solved. Thank you guys for helping me with this. I appreciate your expertise.

 

[bikerider]

I took the boat to the lake yesterday and used the gas motor to get from the ramp to my fishing spot and used it to troll at idle speed for quite a while. There were several times that I shut the motor off while fishing near the shore and restarted it when I wanted to move to a different place. All in all the motor did really well. It started easily and didn't cut out once. The only minor issue I experience with it was it seemed to load up after trolling at idle for a long while but I'm assuming that's to be expected. I noticed that after I turned the plates in the fuel pump over I was no longer getting the inline fuel filter randomly filling and draining. I think the issue with it is solved. Thank you guys for helping me with this. I appreciate your expertise.

 

[km1125]

Glad to hear it's working good again!! Those are great little motors. Thanks for coming back in this the post!