# HELP: Fuel problem Yamaha F70 on ‘13 HB Pro



## VB Fly Fisher

Have you checked or cleaned out the VST filter?


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## topnative2

tarponandtailers said:


> I'm having an issue with fuel supply to the motor. This is on a 2013 HB PRO with 2012Yamaha F70LA (fuel injected) outboard, 180 hrs.
> 
> Motor runs fine for first part of day, I usually run about 15-20 min to my first fishing spot. When I go to jump on plane to hit spot #2, I get up and can usually run before the motor starts stalling, and I lose RPMs. It will fluctuate until it eventually drops way down and I throttle down. If i reach back and pump the bulb while its running, it usually jumps up in RPMs (as it should). If it shuts off, I have to pump the bulb just to get get the boat to start, then need to pump a few times while idling just to keep running. Yesterday after trying the "bulb pumping technique" over and over with no success, I just decided to idle in. After about 3 minutes of easy idling, I decided to just throttle up again to see if there were any changes, and it jumps up to normal RPMs and does great.
> 
> I've already installed a new bulb, new anti siphon valve and new fuel / water separator. Just had 200 hrs service. Run ethanol free with stabilizer. Mechanic mentioned there was a little water in separator and I was hopeful that would be problem, but unfortunately it was not the fix.
> 
> Seems to me like a clogged filter, fuel injector? Something about priming the bulb to push fuel in acts as a stop gap fix, makes me think fuel is inconsistently getting to engine? strange that it fires up immediately at the ramp, and the issues is inconsistent. thought about fuel vents too, but not sure how to check those, they look fine from the outside of the hull when I clean her...
> 
> My knowledge is basic, so I’m grateful for any input and insight, Not really sure where to go next, 🤷‍♂️
> 
> Tight lined and slack wind.


In my experience,,,,,,the fuel h2o separator is "filling up" w/ water and there is not enough fuel passing thru to run the engine at speed. If u are not keeping the tank full condensation will cause a water problem. Also, water may get into the tanks thru the gas cap or water sitting on the fuel gauge.

Get the clear bowl canister for your water seperator and watch it . So when the problem pops up open the knob and drain the water out(tapping on valve w/ a finger).Close it and run it. You may have to do this a several times to clean out the water in the tank.
I just went thru this on a larger motor and it is running fine now.
It does not take a lot of water to create a problem. My problem only occurred at high rpms but ran fine at speed.Good luck


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## tarponandtailers

VB Fly Fisher said:


> Have you checked or cleaned out the VST filter?





VB Fly Fisher said:


> Have you checked or cleaned out the VST filter?


not sure what a VST filter is?
thank you for suggestion


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## tarponandtailers

topnative2 said:


> Thanks Top. I actually got the clear Raycor separator exactly for that reason, I’ll go check. Great suggestion and insight. Maybe from washing bow around gas. cap too much? trying to keep her clean.
> Many thanks.


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## tarponandtailers

tarponandtailers said:


> fuel water separator seems clean, don’t see any water settling at the bottom.


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## topnative2

Also,ck the direction of your tank vent ......


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## topnative2

You may not see it right away. I went thru this same thing last time. I did not see any water but I went thru the process several times and it fixed the problem. I bet your boat was probably sitting for awhile before the problem started or you got a bad load of gas.

Did this issue start after changing the filter?

The vst is a vapor separating tank...google it like I did


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## Water Bound

What type of fuel filter did you put in? I’d had issues once on a larger motor starving at high rpms after change the filter to a Yamaha filter, put a new Sierra on and it ran fine.
IDK, may be worth a try


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## tarponandtailers

Reviewing similar posts seems to suggest. 

My fuel line: has kinked before, so that is possible, should I replace the whole line? 

VST filter: seems common on Yamaha, can ask mechanic to replace this as well

coils: sputters and doesn’t just shut off suddenly, so seems less likely , but not sure 

carb: same as above

fuel injector: seems like low hours for this to be the cause? 

thanks for your advice and insight!


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## topnative2

money bet is water.....but it is a boat after all...K.I.S.S. !


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## Smackdaddy53

tarponandtailers said:


> Reviewing similar posts seems to suggest.
> 
> My fuel line: has kinked before, so that is possible, should I replace the whole line?
> 
> VST filter: seems common on Yamaha, can ask mechanic to replace this as well
> 
> coils: sputters and doesn’t just shut off suddenly, so seems less likely , but not sure
> 
> carb: same as above
> 
> fuel injector: seems like low hours for this to be the cause?
> 
> thanks for your advice and insight!


Yes, change the fuel line, it’s cheap. If your hose has kinked and it was repeatedly kinked the internal liner of the hose could have separated and is collapsing. I have seen this on several boats, one was my buddy’s with an F70. There was a spot under the deck that would kink when he turned one way and we found this after having the same issues you are.


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## topnative2

good time for this>>>>

How A FUEL WATER Separator Works! - YouTube 

Follow These Steps! Why Outboards Run Out Of Fuel! - YouTube


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## topnative2

Smackdaddy53 said:


> Yes, change the fuel line, it’s cheap. If your hose has kinked and it was repeatedly kinked the internal liner of the hose could have separated and is collapsing. I have seen this on several boats, one was my buddy’s with an F70. There was a spot under the deck that would kink when he turned one way and we found this after having the same issues you are.


That is interesting...just never know

BUT..it is a HB!!!!!!!!!!!!!!!!!!


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## coconutgroves

The dreaded Yamaha fuel demand curse.

I've had this on both Yammies I've owned.

First, easy one - check fuel lines. Make sure your bulb is new (you did) and mounted vertical (arrow going up) towards the engine. Now some may think this doesn't matter - but the actual bulb should actually be vertical, standing straight up towards the engine. I had one mounted inline (arrow towards engine), but was upside down. Caused issues with mine for sure. Some may argue this - and horizontal may be fine, just make sure it isn't upside down. That jacks with the siphon flow and check valves in the bulb.

But if you've done that, and all your filters are good, I suggest looking at the low pressure fuel pump. This is what draws fuel from the tank and sends it to your engine. I don't know the F70 that well (had a two stroke 90, have a 115) but there is a diaphragm in it - if this isn't working right, it cannot get enough fuel to the VST. I replaced the entire low pressure fuel pump on my 115 and that solved my issue, but you may be able to just replace this diaphragm:






Yamaha Outboard Parts by HP 70HP OEM Parts Diagram for Fuel | Boats.net


Buy OEM Parts for Yamaha Outboard Parts by HP 70HP Fuel Diagram




www.boats.net





Exposure to heat on a bulb causes issues too. On really hot days, the bulb isn't as firm due to the heat. I always had issues getting enough fuel when it got super hot, so I moved mine to where it is more shaded (this really only happens here in TX when we are 90s to 100s in the summer.

But if I had to bet a beer, it's your low pressure fuel pump.

Note, I am not a mechanic. Just a guy who has owned a lot of boats.


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## Palmetto83

I had this happen a few years ago. The motor operated great at idle and lower rpms. When you’d put the throttle to it would lose prime. You could manually pump the bulb and operate at higher rpms. Ended up being small pin holes in fuel line. Replaced entire line and it solved the problem.


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## topnative2

running fine for 20min....... then something happens...Hmmmmm


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## coconutgroves

topnative2 said:


> running fine for 20min....... then something happens...Hmmmmm


Heat - parts expand


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## tarponandtailers

coconutgroves said:


> The dreaded Yamaha fuel demand curse.
> 
> I've had this on both Yammies I've owned.
> 
> First, easy one - check fuel lines. Make sure your bulb is new (you did) and mounted vertical (arrow going up) towards the engine. Now some may think this doesn't matter - but the actual bulb should actually be vertical, standing straight up towards the engine. I had one mounted inline (arrow towards engine), but was upside down. Caused issues with mine for sure. Some may argue this - and horizontal may be fine, just make sure it isn't upside down. That jacks with the siphon flow and check valves in the bulb.
> 
> But if you've done that, and all your filters are good, I suggest looking at the low pressure fuel pump. This is what draws fuel from the tank and sends it to your engine. I don't know the F70 that well (had a two stroke 90, have a 115) but there is a diaphragm in it - if this isn't working right, it cannot get enough fuel to the VST. I replaced the entire low pressure fuel pump on my 115 and that solved my issue, but you may be able to just replace this diaphragm:
> 
> 
> 
> 
> 
> 
> Yamaha Outboard Parts by HP 70HP OEM Parts Diagram for Fuel | Boats.net
> 
> 
> Buy OEM Parts for Yamaha Outboard Parts by HP 70HP Fuel Diagram
> 
> 
> 
> 
> www.boats.net
> 
> 
> 
> 
> 
> Exposure to heat on a bulb causes issues too. On really hot days, the bulb isn't as firm due to the heat. I always had issues getting enough fuel when it got super hot, so I moved mine to where it is more shaded (this really only happens here in TX when we are 90s to 100s in the summer.
> 
> But if I had to bet a beer, it's your low pressure fuel pump.
> 
> Note, I am not a mechanic. Just a guy who has owned a lot of boats.


Great and really thoughtful response. Interestingly, m after talking to a trusted mechanic, that’s exactly what he suspects as well. 
Thanks for your insight, 🙏👍


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## tarponandtailers

Palmetto83 said:


> I had this happen a few years ago. The motor operated great at idle and lower rpms. When you’d put the throttle to it would lose prime. You could manually pump the bulb and operate at higher rpms. Ended up being small pin holes in fuel line. Replaced entire line and it solved the problem.


That’s great, thank you. I asked my guy exactly this is morning, will check to pressures to make sure no leak. Don’t smell gas anywhere? Did you detect the issue/leak and then replace, or just replace and noticed improvement?


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## Smackdaddy53

tarponandtailers said:


> That’s great, thank you. I asked my guy exactly this is morning, will check to pressures to make sure no leak. Don’t smell gas anywhere? Did you detect the issue/leak and then replace, or just replace and noticed improvement?


Pinholes in the fuel line likely won’t leak and when the engine is pulling fuel it is under a vacuum so you won’t see it leak then either.


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## coconutgroves

tarponandtailers said:


> That’s great, thank you. I asked my guy exactly this is morning, will check to pressures to make sure no leak. Don’t smell gas anywhere? Did you detect the issue/leak and then replace, or just replace and noticed improvement?


Pumping the bulb will also mask the low pressure fuel pump (LPFP) issue since you are increase the pressure to the first pump in the system. Bulb pressure is higher, which in turn pushes more pressure to the LPFP. When I had this issue, I'd pump the bulb while on plane and all was fine, causing me to scratch my head.

If you had a leak in the lines, you'd smell it by now. Even small leaks won't cause issues. And if it were a leak, why does it work fine until 20 minutes later? A leak would be a constant issue, regardless of how much time.

That diaphragm in the low pressure is still my bet - it gets hot and the parts expand - it isn't doing it job when it happens.


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## Palmetto83

tarponandtailers said:


> That’s great, thank you. I asked my guy exactly this is morning, will check to pressures to make sure no leak. Don’t smell gas anywhere? Did you detect the issue/leak and then replace, or just replace and noticed improvement?


Never smelled it or saw anything actually leaking. Started watching the bulb after I pumped it up. You could see it start to slowly inflate


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## DBStoots

I had the same problem a couple years ago with the Yamaha F70 on my Professional. Search around for a post by me with a lot of suggestions similar to those made here. I posted the ultimate solution--seem to recall it was the low pressure fuel pump. If you are in South Florida, I have a great mechanic for you who is mobile.


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## tarponandtailers

DBStoots said:


> I had the same problem a couple years ago with the Yamaha F70 on my Professional. Search around for a post by me with a lot of suggestions similar to those made here. I posted the ultimate solution--seem to recall it was the low pressure fuel pump. If you are in South Florida, I have a great mechanic for you who is mobile.


Thank you kindly, i suspect the LPFP as well. My guy is coming out this Wed. and I will update with the final diagnosis and solution. 
Really appreciate the feedback. 
Tight lines


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## CKEAT

I had this issue on a 12 pro and it was kinked hose that would collapse under load. Replaced with new line / bulb and all was good.


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## tarponandtailers

Just want to thank everyone for their very thoughtful suggestions and input. This is a really great forum, with a lot of collective knowledge. My guy is coming out this week, and I will give a update with the final diagnosis and solution. 
Thank you, tight lines and slack winds.


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## crl.wms

If you have not found a solution, consider the fuel may be getting hot because the water > fuel heat exchanger is plugged up (on the water side) and can't keep the fuel cool enough, heat soak after shut down causes too much vapor and the VST can't clear it. Most everything mentioned would cause problems before the first shut down. The heat exchanger is about the size of a candy bar and has both fuel hoses in / out and water hoses in / out. Can be cleaned out if careful, new about $80 if I remember correctly.


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## manny2376

DBStoots said:


> I had the same problem a couple years ago with the Yamaha F70 on my Professional. Search around for a post by me with a lot of suggestions similar to those made here. I posted the ultimate solution--seem to recall it was the low pressure fuel pump. If you are in South Florida, I have a great mechanic for you who is mobile.


DB, if possible can you please PM me your mechanic’s contact info? Thanks!


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## DBStoots

manny2376 said:


> DB, if possible can you please PM me your mechanic’s contact info? Thanks!


Sent it to you.


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## SkiffaDeeDooDah

Lots of good input here. This forum and the helpful members are awesome! Just a couple more things... If the tank vent line is clogged or blocked, like if a critter got up in there, or a mud dauber built a nest, the fuel system can't breathe. The new EPA carbon canisters can become flooded with fuel and block ventilation too. Also, a friend of mine had similar trouble, and solved the issue by temporarily removing the primer bulb all together, and installing a brass barbed hose coupling in its place. Oh, and IMO, ASV valves are poorly made with dissimilar metals, and destined to fail in a saltwater environment. Just tossing in ideas. Good luck!


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## Brob

tarponandtailers said:


> I'm having an issue with fuel supply to the motor. This is on a 2013 HB PRO with 2012Yamaha F70LA (fuel injected) outboard, 180 hrs.
> 
> Motor runs fine for first part of day, I usually run about 15-20 min to my first fishing spot. When I go to jump on plane to hit spot #2, I get up and can usually run before the motor starts stalling, and I lose RPMs. It will fluctuate until it eventually drops way down and I throttle down. If i reach back and pump the bulb while its running, it usually jumps up in RPMs (as it should). If it shuts off, I have to pump the bulb just to get get the boat to start, then need to pump a few times while idling just to keep running. Yesterday after trying the "bulb pumping technique" over and over with no success, I just decided to idle in. After about 3 minutes of easy idling, I decided to just throttle up again to see if there were any changes, and it jumps up to normal RPMs and does great.
> 
> I've already installed a new bulb, new anti siphon valve and new fuel / water separator. Just had 200 hrs service. Run ethanol free with stabilizer. Mechanic mentioned there was a little water in separator and I was hopeful that would be problem, but unfortunately it was not the fix.
> 
> Seems to me like a clogged filter, fuel injector? Something about priming the bulb to push fuel in acts as a stop gap fix, makes me think fuel is inconsistently getting to engine? strange that it fires up immediately at the ramp, and the issues is inconsistent. thought about fuel vents too, but not sure how to check those, they look fine from the outside of the hull when I clean her...
> 
> My knowledge is basic, so I’m grateful for any input and insight, Not really sure where to go next, 🤷‍♂️
> 
> Tight lined and slack wind.





tarponandtailers said:


> I'm having an issue with fuel supply to the motor. This is on a 2013 HB PRO with 2012Yamaha F70LA (fuel injected) outboard, 180 hrs.
> 
> Motor runs fine for first part of day, I usually run about 15-20 min to my first fishing spot. When I go to jump on plane to hit spot #2, I get up and can usually run before the motor starts stalling, and I lose RPMs. It will fluctuate until it eventually drops way down and I throttle down. If i reach back and pump the bulb while its running, it usually jumps up in RPMs (as it should). If it shuts off, I have to pump the bulb just to get get the boat to start, then need to pump a few times while idling just to keep running. Yesterday after trying the "bulb pumping technique" over and over with no success, I just decided to idle in. After about 3 minutes of easy idling, I decided to just throttle up again to see if there were any changes, and it jumps up to normal RPMs and does great.
> 
> I've already installed a new bulb, new anti siphon valve and new fuel / water separator. Just had 200 hrs service. Run ethanol free with stabilizer. Mechanic mentioned there was a little water in separator and I was hopeful that would be problem, but unfortunately it was not the fix.
> 
> Seems to me like a clogged filter, fuel injector? Something about priming the bulb to push fuel in acts as a stop gap fix, makes me think fuel is inconsistently getting to engine? strange that it fires up immediately at the ramp, and the issues is inconsistent. thought about fuel vents too, but not sure how to check those, they look fine from the outside of the hull when I clean her...
> 
> My knowledge is basic, so I’m grateful for any input and insight, Not really sure where to go next, 🤷‍♂️
> 
> Tight lined and slack wind.





tarponandtailers said:


> I'm having an issue with fuel supply to the motor. This is on a 2013 HB PRO with 2012Yamaha F70LA (fuel injected) outboard, 180 hrs.
> 
> Motor runs fine for first part of day, I usually run about 15-20 min to my first fishing spot. When I go to jump on plane to hit spot #2, I get up and can usually run before the motor starts stalling, and I lose RPMs. It will fluctuate until it eventually drops way down and I throttle down. If i reach back and pump the bulb while its running, it usually jumps up in RPMs (as it should). If it shuts off, I have to pump the bulb just to get get the boat to start, then need to pump a few times while idling just to keep running. Yesterday after trying the "bulb pumping technique" over and over with no success, I just decided to idle in. After about 3 minutes of easy idling, I decided to just throttle up again to see if there were any changes, and it jumps up to normal RPMs and does great.
> 
> I've already installed a new bulb, new anti siphon valve and new fuel / water separator. Just had 200 hrs service. Run ethanol free with stabilizer. Mechanic mentioned there was a little water in separator and I was hopeful that would be problem, but unfortunately it was not the fix.
> 
> Seems to me like a clogged filter, fuel injector? Something about priming the bulb to push fuel in acts as a stop gap fix, makes me think fuel is inconsistently getting to engine? strange that it fires up immediately at the ramp, and the issues is inconsistent. thought about fuel vents too, but not sure how to check those, they look fine from the outside of the hull when I clean her...
> 
> My knowledge is basic, so I’m grateful for any input and insight, Not really sure where to go next, 🤷‍♂️
> 
> Tight lined and slack wind.


I’ve been having the same issues with my 2016 Pro with an F70. 
I’ve changed the pick-up tube in the fuel tank, all the fuel lines. Just did another 100hr service so it’s got a new water separator. 
Ran great for several motor hours then started acting up again yesterday. 
I’m gonna start with repositioning the bulb. I know mine is sitting horizontal now. 
I’ll run it again tomorrow and let you know.


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## Smackdaddy53

Brob said:


> I’ve been having the same issues with my 2016 Pro with an F70.
> I’ve changed the pick-up tube in the fuel tank, all the fuel lines. Just did another 100hr service so it’s got a new water separator.
> Ran great for several motor hours then started acting up again yesterday.
> I’m gonna start with repositioning the bulb. I know mine is sitting horizontal now.
> I’ll run it again tomorrow and let you know.


Get that bulb as vertical as possible running “uphill”.


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## Backlasher

Not sure if this was mentioned but I joined the crowd as I also experienced a few issues with fuel starvation on my F70. I added a Racor S3213 (with clear bowl and stainless bracket) and haven't seen any water in the fuel after several years of ownership. I do change out the filter body annually however after experiencing the problems mentioned above, I replaced the small Yamaha fuel filter found under the cowling and that seems to have cured my starvation issues.

I do have the squeeze bulb mounted vertically but still running the original bulb and fuel lines - while using corn juice.

Now if I could just solve the starting issue I have (engine starter solenoid clicks but engine won't turn over) when the boat sits for several weeks....


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## mwolaver

Last time I had a "fuel" issue with an outboard, I went ahead and bought a 6 gallon tank with it's own fuel line. Using that will cut your possible issues in half and allow you to work the correct half.


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## PoonHunterFishing

@tarponandtailers did you ever find your problem?

I have what seems to be the exact same issue on my 17 F70LA. I've replaced almost everything up to the engine. Fuel lines, primer bulbs (haven't mounted vertically yet), asv, fuel pickup, and the last thing replace was the low pressure fuel pump. 

That seemed to do the trick for about 5 or 6 months and then my issues started reoccurring which makes me think maybe it was just disguising the true issue.

The next step I plan on trying is cleaning/replacing filters in the vst. I would also like to try to bench test the fuel pump in the vst if I can find a way to do that. 

It appears as though there's been no posts for about a year though which makes me think your issue may have actually been solved. If you get this message please let me know what worked for you.

Thanks!


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## tarponandtailers

PoonHunterFishing said:


> @tarponandtailers did you ever find your problem?
> 
> I have what seems to be the exact same issue on my 17 F70LA. I've replaced almost everything up to the engine. Fuel lines, primer bulbs (haven't mounted vertically yet), asv, fuel pickup, and the last thing replace was the low pressure fuel pump.
> 
> That seemed to do the trick for about 5 or 6 months and then my issues started reoccurring which makes me think maybe it was just disguising the true issue.
> 
> The next step I plan on trying is cleaning/replacing filters in the vst. I would also like to try to bench test the fuel pump in the vst if I can find a way to do that.
> 
> It appears as though there's been no posts for about a year though which makes me think your issue may have actually been solved. If you get this message please let me know what worked for you.
> 
> Thanks!


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## tarponandtailers

Elusive problem to diagnose and fix. Ultimately seems like it’s the VST or pressure fuel . If i idle after running, before shutting down seems to help (letting engine cool just a bit) and if that doesn’t work, i have to reprime the bulb when i start back up. I think the engine heats up, and the fuel delivery becomes insufficient, but I’m not mechanically savvy. My mechanic says this is a known problem with these. 
Ultimately, no final fix, but at least have a work around.


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## PoonHunterFishing

tarponandtailers said:


> Elusive problem to diagnose and fix. Ultimately seems like it’s the VST or pressure fuel . If i idle after running, before shutting down seems to help (letting engine cool just a bit) and if that doesn’t work, i have to reprime the bulb when i start back up. I think the engine heats up, and the fuel delivery becomes insufficient, but I’m not mechanically savvy. My mechanic says this is a known problem with these.
> Ultimately, no final fix, but at least have a work around.


Wow I was hoping there was a final solution but that's still really good info. Thanks for responding and letting me know. 

I'm going to keep chopping away at it and if I find anything that may be helpful to either of us I'll post it to the thread. 

Tight lines.


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## sjrobin

Yamaha F series have three fuel filters under the cowling. You should do everything possible to keep water or sediment from reaching any of them. This means buying your fuel from a station with high turnover ethanol free not required. This means keeping your fuel tank full even when you are too tired to stop and refuel after a day on the water. Replace your tank filter annually. Clear Racor bowl is good practice. Yamaha F series require a Yamaha fuel additive to keep injectors clean. Use it every time you add fuel. Doesn't hurt to use Star Tron fuel stabilizer with every tank. Do these steps and you will not have many problems. All other brand outboards are a different story.


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## Frank Ucci

There is a fuel cooler on your engine. It circulates water and fuel through a heat exchanger (fuel cooler) to prevent the fuel from overheating. The water side of the heat exchanger can become clogged with mud and debris. Once it is clogged, it will no longer cool the fuel and the fuel will begin to vaporize in the lines. Have you checked to be sure the fuel cooler is not clogged?


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## PoonHunterFishing

Frank Ucci said:


> There is a fuel cooler on your engine. It circulates water and fuel through a heat exchanger (fuel cooler) to prevent the fuel from overheating. The water side of the heat exchanger can become clogged with mud and debris. Once it is clogged, it will no longer cool the fuel and the fuel will begin to vaporize in the lines. Have you checked to be sure the fuel cooler is not clogged?


I have not yet checked that but I was planning to do it soon. It definitely does seem like it could be a root cause to fuel overheating if that's what is causing our issue.

I assume that the heat exchanger is not inline with the tell tale? If so and it were clogged the motor wouldn't pee right? Im just waiting for the shop that has my boat (no help at all) to give me a good time to go pick it up then I'll start digging into the heat exchanger and other possibilities.


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## BrownDog

PoonHunterFishing said:


> I have not yet checked that but I was planning to do it soon. It definitely does seem like it could be a root cause to fuel overheating if that's what is causing our issue.
> 
> I assume that the heat exchanger is not inline with the tell tale? If so and it were clogged the motor wouldn't pee right? Im just waiting for the shop that has my boat (no help at all) to give me a good time to go pick it up then I'll start digging into the heat exchanger and other possibilities.


fuel cooler is by/ behind VST and looks like an aluminum box. Both it and the VST are easy to clean, most frustrating part is getting the intake off.

just went through these same symptoms: cleaned/replaced every filter, fuel cooler, VST no real change. Then replaced primer bulb and low pressure pump, one of these seemed to have done the trick.


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## tarponandtailers

Frank Ucci said:


> There is a fuel cooler on your engine. It circulates water and fuel through a heat exchanger (fuel cooler) to prevent the fuel from overheating. The water side of the heat exchanger can become clogged with mud and debris. Once it is clogged, it will no longer cool the fuel and the fuel will begin to vaporize in the lines. Have you checked to be sure the fuel cooler is not clogged?


no but engine temp never rises
doesn’t seem to


BrownDog said:


> fuel cooler is by/ behind VST and looks like an aluminum box. Both it and the VST are easy to clean, most frustrating part is getting the intake off.
> 
> just went through these same symptoms: cleaned/replaced every filter, fuel cooler, VST no real change. Then replaced primer bulb and low pressure pump, one of these seemed to have done the trick.


I think it’s the low pressure pump. 
I replaced my primer and problem remained. 
My research on these engines hints at the low pressure pump


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## BrownDog

tarponandtailers said:


> no but engine temp never rises
> doesn’t seem to
> 
> I think it’s the low pressure pump.
> I replaced my primer and problem remained.
> My research on these engines hints at the low pressure pump


If changing the LP pump check your oil to make sure there is no fuel in it.


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## PoonHunterFishing

One of the shops I've taken my boat to changed my lp pump (under warranty) and that seemed to solve my problem for about 5 or 6 months and it recently returned which leads me to believe either i got a defective pump or it just masked my problem for a little while.


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## tarponandtailers

PoonHunterFishing said:


> One of the shops I've taken my boat to changed my lp pump (under warranty) and that seemed to solve my problem for about 5 or 6 months and it recently returned which leads me to believe either i got a defective pump or it just masked my problem for a little while.


did you ever make any more progress here? 
i’m looking to replace the low pressure pump 🤞


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## PoonHunterFishing

tarponandtailers said:


> did you ever make any more progress here?
> i’m looking to replace the low pressure pump 🤞


I haven't been able to do much lately because I'm preparing for a move but this is what I've found during my troubleshooting.

When taking the gas cap off I realized I could hear oxygen being pulled into the tank which indicates to me that instead of venting to atmospheric pressure, the tank is pulling a vacuum. 

That would make sense to me as to why replacing my low pressure pump worked temporarily and now I'm starting to have issues again. 

The design of my system has it venting through the perko gas cap. Perko says the caps are designed to vent pressure or vacuum at approximately 1 psi which can't be happening if I'm hearing it pull air when I remove the cap ( at least theoretically). So I've recently replaced the cap but I haven't had the opportunity to take it out again yet. 

I'll be sure to respond as soon as I have the chance to go out and run it. 

One more thing, if you haven't already, it may be worth just replacing the diaphragm in your low pressure pump. $15 diaphragm costs as opposed to the cost of the new pump.


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## tarponandtailers

PoonHunterFishing said:


> I haven't been able to do much lately because I'm preparing for a move but this is what I've found during my troubleshooting.
> 
> When taking the gas cap off I realized I could hear oxygen being pulled into the tank which indicates to me that instead of venting to atmospheric pressure, the tank is pulling a vacuum.
> 
> That would make sense to me as to why replacing my low pressure pump worked temporarily and now I'm starting to have issues again.
> 
> The design of my system has it venting through the perko gas cap. Perko says the caps are designed to vent pressure or vacuum at approximately 1 psi which can't be happening if I'm hearing it pull air when I remove the cap ( at least theoretically). So I've recently replaced the cap but I haven't had the opportunity to take it out again yet.
> 
> I'll be sure to respond as soon as I have the chance to go out and run it.
> 
> One more thing, if you haven't already, it may be worth just replacing the diaphragm in your low pressure pump. $15 diaphragm costs as opposed to the cost of the new pump.


Thanks for your response. I agree about maybe being the vents as well. I am thinking I may replace/clean the vents and the low pressure pump. Let me know the you run it. I'll do the same


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## PoonHunterFishing

tarponandtailers said:


> Thanks for your response. I agree about maybe being the vents as well. I am thinking I may replace/clean the vents and the low pressure pump. Let me know the you run it. I'll do the same


I got it out yesterday actually. I ran for an hour and a half at wot with no issues. 

I don't want to say it's fixed yet but I feel like it would have died with the old gas cap. Gonna have to go out and test more.

I did notice that I had no more vacuum noise when removing the gas cap so that gives me hope.

I'll keep you updated the next time I get out.


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## tarponandtailers

Roger that. I'm hopeful you nailed it. Seems to make sense. Thanks for the feedback


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## capt_chummy

I have a 2016 Yamaha F70 with 300 hours and experienced some problems with it dying on idle and would not restart. This was about three years ago, and I was running ethanol fuel. I was able to overcome it by pumping the hell out of the fuel bulb and the engine finally restarted. I switched to ethanol free fuel and had no problems for three years. Last weekend I filled the boat with gas at a dock and dealt with the same problem the next day after three years of it being trouble free. I topped off later with ethanol free fuel again and the boat ran great the next day. I suspect it's a vapor lock issue with the higher ethanol gas but I would like to know if anyone has had the same experience with fuel in this engine. It seems to be extremely fuel sensitive.


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