F70 Leaking Fuel/Loss of power

[benpaschal]

Hi everyone,

I have a 2016 F70 that is about one year old. It has 580 hours and is used often. I have taken my motor in to the local yamaha dealer on two different occasions with no luck. All symptoms are occasional which is making this a tough one! The dealer changed the two in motor fuel filters.

I keep up with recommended routine maintenance and change the fuel/water separator routinely.

Here are the symptoms:
1. Occasional loss of power. I get up on plane and motor shuts down to idle after running for 30 sec-1 minute. No alarms. I usually just squeeze the ball as it is sometimes soft and get back up on plane and problem goes away. This will happen sometimes 0-2 times per day but never consecutively.

2. Occasional rough idle

3. Gas will drip from drain hole under the cowling. I will make a long run (30-40 minutes) to a fishing spot. I trim the motor up to fish an area and several hours later when I trim the motor back down I notice several spoonfuls of gas dripping from the front drain hole of the motor under the cowling. I have removed cowling and checked for leaks but can't find any. This has been happening about once or twice per day for the last several days.

4. gas ball is occasionally soft


After several hours of searching online and speaking with some mechanically inclined friends, I suspect it is a clogged injector which is bleeding gas. From info I have gleaned on forums, maybe a VST needle is stuck and leaking gas?

Thoughts or suggestions much appreciated!

Thanks,
Ben

[boscoe99]

Hi everyone,

I have a 2016 F70 that is about one year old. It has 580 hours and is used often. Sounds like a commercially used motor! Most recreational users won't log that much time in ten years. I have taken my motor in to the local yamaha dealer on two different occasions with no luck. All symptoms are occasional which is making this a tough one! The dealer changed the two in motor fuel filters.

I keep up with recommended routine maintenance and change the fuel/water separator routinely.

Here are the symptoms:
1. Occasional loss of power. I get up on plane and motor shuts down to idle after running for 30 sec-1 minute. No alarms. I usually just squeeze the ball as it is sometimes soft and get back up on plane and problem goes away. This will happen sometimes 0-2 times per day but never consecutively. Having to use the primer ball tends to indicate to me that perhaps the fuel pump is not doing its job. Or maybe there is an intermittent air leak in the fuel system that is preventing the lift pump from doing its job all of the time.

2. Occasional rough idle

3. Gas will drip from drain hole under the cowling. I will make a long run (30-40 minutes) to a fishing spot. I trim the motor up to fish an area and several hours later when I trim the motor back down I notice several spoonfuls of gas dripping from the front drain hole of the motor under the cowling. I have removed cowling and checked for leaks but can't find any. This has been happening about once or twice per day for the last several days. Leaks are hard to find but you need to keep looking. When the cowling gets blown off and the motor is on fire it will be even harder to find the source of the leak. You will easily spot the leakage that is in your pants. They make dyes that can be added to gasoline which might make it easier to spot the source of the leak.

4. gas ball is occasionally soft Not abnormal when the lift pump is pulling gasoline and the pressure in the ball has been lowered.

After several hours of searching online and speaking with some mechanically inclined friends, I suspect it is a clogged injector which is bleeding gas. Put a fuel pressure gauge on the fuel rail. Turn the key on. The pressure should increase to a specified value. Monitor the gauge to see what the pressure does. It should remain somewhat steady for a period of time. If pressure falls off fairly quickly that is a source of a fuel system leak. Could be an injector that is not closing as it should. From info I have gleaned on forums, maybe a VST needle is stuck and leaking gas?

Thoughts or suggestions much appreciated!

Thanks,
Ben

You can plumb in a clear section of fuel hose to monitor for the presence of air leaks within the fuel system. Install a fuel pressure gauge to monitor the output pressure from the electric fuel pump.

I would first find and fix the leak. That is the most pressing issue and it might be the source of your operational problems.

[rodbolt17]

check the charcoal canister for the presence of raw gasoline.
if the VST needle is leaking it will overfill the canister, which is NOT supposed to ever have liquid in it.
I would not lean so much to a leaking injector as it would leak into the cyl head and intake runner.
next time you shut it down remove the cowl and observe the intake runner and air box.

[benpaschal]

Rodbolt and Boscoe,

Thanks for the information. I took it to the local yamaha dealer and upon further inspection they now said the VST float was dirty which was keeping it open and causing gas to leak out. They also said the VST tank was dirty and full of shell bits which made it difficult for the water to cool off gas causing loss of power. Hope that is correct, i will be on the water today and will find out if they fixed issue soon enough!

[99yam40]

sounds like the fuel cooler had the shell in it not the VST.
should not have bits of shell in the fuel.

Also trash in needle and seat is more probable than dirty float