confirm fuel system air leak

[onoisland]

I have a 2011 115 HP Yamaha outboard. Last time I was out on the water, the engine ran fine at first. Went 4 miles, stopped for 1 hour, started up, went 5 more miles, stopped for 1 hour and then started engine to come home. Engine would not go over 2000 RPM. If I tried to push the throttle, the engine would sputter. The fuel fill bulb was soft.

I suspect an air leak in the fuel line. At home, I removed the engine cowling and found the translucent fuel filter housing on the back of the engine. I pumped the fuel fill bulb till it was hard and the translucent fuel filter housing was completely full. Then I ran the engine at idle, Within 1 minute, I see the fuel level in the translucent filter housing drop by 3/4 of an inch. I can pump the bulb and it refills to the top. I also used the bulb to pump fuel into a glass jar; there was no water in the gas.

Does this seem like an air leak in the fuel lines before the engine? I suspect it is the fuel lines connection to the bulb. When the engine is turned (via the steering wheel). it puts a lot of stress on the lines as they connect to the bulb..

[boscoe99]

Nope, that is not indicative of an air leak. It is the way the system works.

But the motor should not put a strain on the fuel hose when the motor is turned hard to port or starboard. That needs to be fixed.

If someone pumps the primer ball when the motor is running does the sputtering go away or is it still there?

[onoisland]

Hmm... So are you saying the translucent fuel filter housing is supposed to run with air in the top 3/4 of and inch that I can see? Or is it supposed to remain completely full of fuel (with no air in it at all).

When I had the problem, I think I might have pressed the bulb a few times but I did not make a concerted effort to use it to pump fuel to the engine... I don't remember it helping... To be honest, at the time, the engine was running and all I wanted to do at the time was get home..

[pstephens46]

My engine mounted fuel filter also has the air gap at top that you mention. It runs fine. Looks like the problem is elsewhere....

[onoisland]

Dang... thought I had found my problem... That said... Is there an easy (or hard way) to find if I do have an air leak? For example, can I apply air pressure to the fuel line and put a liquid soap solution on suspect areas and look for bubbles? I am grasping for solutions here...

[99yam40]

if worried about fuel problem, I would monitor fuel pressures.

but being you say limited to 2000 might mean there is an overheat or oil level problem.
do you have gauges that will show if this is happening?
do you have a buzzer/alarm on this rig?
does it work properly?

a soft bulb mean nothing as it is on the suction side of the pump

[onoisland]

Right after I had the problem, I got the boat on the trailer and brought it home.... plugged in a garden hose to flush the engine,,, I was told I could run the engine while on the hose but not to run it too much?? (don't know what that meant but that is what the dealer told me).... But I did run it and I reved the engine in gear a few times to almost 4000 RPM...

I think the problem may only occur under load...

I have a big (4 inches in diameter and 8-10 inches long) Yamaha spin on water separating fuel filter in the boat (and off course the small fuel filter on the engine itself). The spin on filter only has about 30-40 hours of use on it over about a year of time... I don't use this boat as much as my big trawler...

I have not tried replacing the spin on yet... as I said I took a glass jar and squeezed the bulb and pumped about a pint of fuel out. It was clear of water... besides I had just filled the tank with non-ethanol gas the week before..

Should I change the spin on and check it for water?

Does anyone still think it might be an air leak in the line?

I need to run it again on the garden hose... not sure if it is missing at idle... if it is, when I ran it earlier today,, it was not noticeable...

[onoisland]

no real gauges on this boat,,, a basic 18 foot Sea Hunt for playing in the bays.... The translucent "bowl" on the engine where the on-engine fuel filter is has what appears to be wires and a sensor in the bottom of the bowl.. I assume that is to sense water and shut down the engine if water gets this far. I assume the engine has internal fail safes to shutfdown on over temp or low oil pressure,,, I am guessing,, To be honest, I am very much a novice on outboards... I am more expert on my diesel engines in my trawler,,

[rodbolt17]

no "shut downs" for any alarm.
RPM reduction for a few.
water detect will only work in N gear position.

[pstephens46]

If engine mounted filter is getting fuel I would imagine the issue is between there and injectors. I would Not rev an engine on trailer with muffs In Gear to 4000rpm....

[99yam40]

you mentioned oil pressure, so maybe this is a 4 stroke.
it is always best to post a complete motor model # when asking questions so everyone knows what motor you are talking about
Install proper gauges and monitor when the problem shows up. they will tell you something about what is going on

[onoisland]

in my original post I mentioned it was a 2011 115 HP Yamaha... to my knowledge only 4 strokes were made on that date

[99yam40]

My guess is that may be true for some areas of the world, but not sure all of them
For all I know you are located on an island in the middle of nowhere

[onoisland]

Thanks to all for the education and ideas,,,, I guess I need to put the boat back in the water and run it some more to reproduce the problem,,,

A year ago I had a similar problem and at that time the boat was due for its 2 year service anyway so I took it in to an authorized dealer.... They did the 2 year service and launched the boat and ran it in the water for a while... said they had no problem and could find no reason I had problems... cost me over $600... That service was a year ago and only 30-40 hours were put on the engine since then...

I can only guess it is a fuel delivery problem... air leak... vapor lock... I have no idea... Just know that there is fresh non-alcohol fuel in the boat (filled it a week before I took it out)... when I removed the bowl on the engine and used the bulb to pump fuel into a gas container the fuel was clean and clear of any water...

Because the fuel pumped (via the bulb) in great quantities I do not think I have a fuel line restriction... but who knows... I did think about taking a portable fuel tank with me (as advised by others) but that would require me to cut the existing fuel lines ( all existing fuel line connections are factory crimped and there are no hose clamps I can easily remove to insert the portable fuel supply).

When I take it out for the test run,,, will stay close to the dock... if the problem reoccurs I will pump the bulb a lot to see what that does...

I find it strange that the translucent bowl containing the on-engine filter on the back of the engine runs with air in it... others say theirs has air and theirs run fine... that is so strange,,, the fuel level in that bowl once it goes down (after 1 minute of engine idling) is below the level of the filter itself...

[boscoe99]

If in the USA your model is an F115TLR/F115TXR.

If outside of the USA it is more than likely an F115AET.

115 two strokes are still being made and sold by Yamaha. Just not here in the US. As Yam99 notes, when people ask questions we have no idea where in the world they are writing from.

A 115 denotes a two stroke. An F115 denotes a four stroke. There is now also a VF115 model. Different from the F115.

If any air were to be in your fuel system it would be purged by the vapor separator tank. That is one function of the VST. You can plumb a section of clear plastic hose into the fuel supply line and monitor it for the presence of air bubbles if you think this is the problem.