2011 - F70LA, 4 stroke low speed fuel issue.

[jtmac2011]

Need assistance, 2011 - F70LA, 4 stroke low speed fuel issue. Outboard runs great at high rpm, no issues to speak of. However, at low rpm (I.E. while at low speed in gear) the engine will starve itself of fuel after 10 minutes of operation. When this occurs the VST is refilled using the primer bulb and the engine can then be restarted without issue; but, will only run for another 10 minutes at low rpm before sputtering and stalling again. I can perform this recharge numerous times with the same outcome (Note: This only occurs if I remain at low rpm, if I open up the throttle after starting the fuel problem disappears until I bring it back to low rpm). I used a portable tank to bypass the on board fuel storage and delivery system but results were the same. Yamaha dealer has tried on numerous visits (about 8 visits over the past year) to repair the problem but the issue persists. Low pressure lift pump has been replaced and all related fuel system components either cleaned or replaced.

[Tony Harper]

Need assistance, 2011 - F70LA, 4 stroke low speed fuel issue. Outboard runs great at high rpm, no issues to speak of. However, at low rpm (I.E. while at low speed in gear) the engine will starve itself of fuel after 10 minutes of operation. When this occurs the VST is refilled using the primer bulb and the engine can then be restarted without issue; but, will only run for another 10 minutes at low rpm before sputtering and stalling again. I can perform this recharge numerous times with the same outcome (Note: This only occurs if I remain at low rpm, if I open up the throttle after starting the fuel problem disappears until I bring it back to low rpm). I used a portable tank to bypass the on board fuel storage and delivery system but results were the same. Yamaha dealer has tried on numerous visits (about 8 visits over the past year) to repair the problem but the issue persists. Low pressure lift pump has been replaced and all related fuel system components either cleaned or replaced.

It will be one of 2 things, either the fuel cooler is blocked or the engine low pressure fuel filter mounted on the tappet cover, most likely will be the low pressure fuel filter, the filter top can have a crack & suck air, I have this exact problem multiple times with customers engines, the crack is normally not even visable, microscopic ?? for want of a better word, to confirm this fault you would need to replace the filter top, but that filter top is only available as a filter/cup assy which is quite expensive, try using the 6R3-24560-00 fuel filter assy, remove the bowl off that filter & refit the original sensor bowl, the fault is always only in the filter top anyway.

I will always check/clear the fuel cooler first and if the fault still occurs, then I do the low pressure fuel filter replacement.

Let us know any outcome if you try these.

[jtmac2011]

Thank you, I will advise the Yahama Dealer of your advice. Boat is in the shop now. Will get back in touch.

[Tony Harper]

any updates on the one yet ??

[Enginetrouble]

Hi,
I have the same problem with my F60 2005. I have already replaced the low pressure fuel filter. Maybe you can give me advice on how to clean the fuel cooler?

[Tony Harper]

Hi,
I have the same problem with my F60 2005. I have already replaced the low pressure fuel filter. Maybe you can give me advice on how to clean the fuel cooler?

can you please advise what your engine MODEL NUMBER is, the 2005 model year F60 has both carby models & EFI models, ONLY the EFI model has a fuel cooler, so see how VERY IMPORTANT it is to ALWAYS provide the MODEL NUMBER when asking questions

[jtmac2011]

Update, no luck with the 2 suggested fixes. Same issue persists. But the fuel cooler provided another thought for possible repair, could the water pump not provide enough water at low speed? There is definitely a connection with heat...I.E. after start up the fuel problem does not occur until after engine is fully warm, then the 10 minute run time intervals begin.

[99yam40]

does the lift pump run at low RPM at all?

measuring amps of the lift pump or fuel pressure to VST should tell that
some run all the time above idle, but on and off at idle

[jtmac2011]

Lift pump was changed and yes it does run all the time. Techs indicated that both low and high fuel pressure are fine at start up at the shop and they can't duplicate the problem while the boat is at dry dock. When out on water the problem couldn't be duplicated on the first run, second run, engine cover left off and all testing equipment hooked up but again no duplication of problem. 3rd attempt, cover left on and ran for over an hour problem finally duplicated but Tech not available (why no tech on board who knows), 4th attempt was performed after the suggested fixes and problem repeats itself. At this point service is at a standstill.

[99yam40]

have to be monitoring pressures when the problem shows up

if priming with the bulb has to be done after it shuts down, the lift pump is not working properly to keep the VST filled.
does pumping the bulb help while this keeps repeating itself as you said?

[jtmac2011]

When problem occurs, yes the only way to restart is to prime bulb. It takes about 17 squeezes on the bulb to fill the VST, anything less you don't get 10 minutes of additional run time.

Not sure if heat is a result of the problem, but on 2 occasions the engine was run well over an hour (closer to 2 hours) with the engine cover removed and the problem didn't repeat itself (on one of those occasions it was after the initial problem started).

Tech also charged the system with fuel and then removed the line from the fuel hose connector at the front of the engine. He then pressurized the fuel system with low pressure air from the same disconnected fuel line. No fuel leaks found with about 50 psi of air pressure behind the fuel.

[99yam40]

When problem occurs, yes the only way to restart is to prime bulb. It takes about 17 squeezes on the bulb to fill the VST, anything less you don't get 10 minutes of additional run time.

Not sure if heat is a result of the problem, but on 2 occasions the engine was run well over an hour (closer to 2 hours) with the engine cover removed and the problem didn't repeat itself (on one of those occasions it was after the initial problem started).

Tech also charged the system with fuel and then removed the line from the fuel hose connector at the front of the engine. He then pressurized the fuel system with low pressure air from the same disconnected fuel line. No fuel leaks found with about 50 psi of air pressure behind the fuel.

so what does that point to in your mind?

to me it means the lift pump is not running when it should some times or sucks air instead of fuel sometimes.
how do you find out?
monitor lift pump current and pressure to see if is running when it should be.
recording device would ne nice

I am sure they can hook test equipment up and still put the cowling back on and let someone that has the time to run the thing till it has a problem and see what the pump is doing when the problem shows up
if you have more time and it is less cost to you for you to drive it around instead of them so be it.
you just need to know what to be looking at and for.

also there is a difference in pressure leaks and vacuum leaks

[jtmac2011]

Question: What drives the lift pump? I know its mechanical and I am assuming an eccentric (cam) of some sort is driving from beneath. Could the cam be worn, obviously I am guessing at this point.

[jtmac2011]

I will also arrange time to go out with the tech and his testing equipment. This is getting frustrating!! We will get this beat, but we need to arrange the time.

[99yam40]

I thought it was electric, so I have no idea