Fuel issue

[jethro1]

I think what you are seeing is completely normal.

I am more familiar with Yamaha four strokes but virtually every Yamaha filter will do/show exactly what your motor is doing/showing.

If the motor starts, idles and runs well for long periods of time you do not have a problem.

[gatorglenn]

I think what you are seeing is completely normal.

I am more familiar with Yamaha four strokes but virtually every Yamaha filter will do/show exactly what your motor is doing/showing.

If the motor starts, idles and runs well for long periods of time you do not have a problem.

Ok, anyone know what this black stuff is. Contaminants from the breakdown of ethanol.

[jethro1]

My guess would be carbon dust from the brushes in the electric fuel pump. Gasoline flows through the pump to cool and lubricate it. Some of the gasoline that flowed through the pump gets sent back to the VST by the fuel pressure regulator. Hopefully the VST filter captures any dust that does not settle to the bottom of the VST.

[gatorglenn]

My guess would be carbon dust from the brushes in the electric fuel pump. Gasoline flows through the pump to cool and lubricate it. Some of the gasoline that flowed through the pump gets sent back to the VST by the fuel pressure regulator. Hopefully the VST filter captures any dust that does not settle to the bottom of the VST.

Where Iam seeing the most is in the site bowl fuel filter. Before it gets to the VST.

[EuropeanAM]

Degraded rubber fuel line material.

Likely from lines between tank and primer bulb... but can also be caused by degrading fuel filler hose and/or vent hose.

Check tank itself for similar substance... if present in tank, it's likely from the filler hose and/or vent hose (if NOT present, it's from the fuel lines).

[gatorglenn]

Degraded rubber fuel line material.

Likely from lines between tank and primer bulb... but can also be caused by degrading fuel filler hose and/or vent hose.

Check tank itself for similar substance... if present in tank, it's likely from the filler hose and/or vent hose (if NOT present, it's from the fuel lines).

Thanks

[jethro1]

Sorry, I thought that stuff was being found in the bottom of the VST. If it is found in the bottom of the primary fuel filter then I agree it is probably fuel hose or primer ball internal degradation. Actually from any parts that are upstream from the filter. Might even be coming from the fuel supplier.

[gatorglenn]

Ok this was how it ran for about 10 mins. Then it started the stumbling issue when going from RPMs down to Idol. And surging at RPMs up and down. That Schrader valve on the VST tank started leaking at the same time it start running bad. I'm thinking the pressure valve is actually sticking. So I'm assuming the only thing left in the VST tank is the fuel pump and the pressure valve. I'm just going to go ahead and replace those and I'll have a complete new fuel system. And hopefully problem solved.

[EuropeanAM]

Why not put a fuel pressure gauge on it, and monitor the pressure to see what is actually happening?

[gatorglenn]

Why not put a fuel pressure gauge on it, and monitor the pressure to see what is actually happening?

Going to, thanks

[gatorglenn]

Well this is what it's been doing. And fuel pressure is supposed to be between 45 and 55. The actual pressure at Idol and over 5000 RPMs is at 44. Turning the key on the pressure will go up to 44 but then falls to 40 and sits there. Thoughts

[gatorglenn]

This is where it falls to with key on.

[gatorglenn]

This is idle and wide-open throttle, pressure doesn't change.

[EuropeanAM]

You're fine. Fuel pressure specification is 42-44 psi, engine running.

Be careful about revving the engine like that without a load....

[gatorglenn]

Thanks but that stumbling going down to idle is with a load on lake to. I can't find it. But still looking. It just doesn't run right. All shops are full with winterizing. So it will go in when they get time.

[EuropeanAM]

That stumbling is likely related to the throttle stop on the throttle plate. Proper adjustment requires use of the Computer Diagnostic System, monitoring of TPS, RPM and IAC Duty Cycle, and a working knowledge of how those data items interact.

Relatively common in this vintage, though seldom pointed out unless the engine "stalled".

[gatorglenn]

That stumbling is likely related to the throttle stop on the throttle plate. Proper adjustment requires use of the Computer Diagnostic System, monitoring of TPS, RPM and IAC Duty Cycle, and a working knowledge of how those data items interact.

Relatively common in this vintage, though seldom pointed out unless the engine "stalled".

thanks Don, I appreciate it. I will note that for the mechanics when it gets to the shop thank you sir.

[gatorglenn]

Update,
After talking to a Mercury tech. He said all I needed was fuel flush on the fuel tank. So I will be dismantling the rear of the boat, and taking the fuel tank out this winter. He recommended I run a mixture of 1 gallon Seafoam, and 1 gallon of fuel. Putting the motor in as much load as I could with being tucked under. And keep the RPMs above 3000. Halfway through this mixture the motor was starting to run a lot better. Once done, refueled with clean fuel. Motor ran flawless! So I will be looking for a new fuel tank that's only about 9 to 12 gallons. I ran the mixture on a portable tank. The hard thing will be finding one that can actually fit my fuel port I have now. Issues with fuel are fixed.

[Lowerider58]

Update,
After talking to a Mercury tech. He said all I needed was fuel flush on the fuel tank. So I will be dismantling the rear of the boat, and taking the fuel tank out this winter. He recommended I run a mixture of 1 gallon Seafoam, and 1 gallon of fuel. Putting the motor in as much load as I could with being tucked under. And keep the RPMs above 3000. Halfway through this mixture the motor was starting to run a lot better. Once done, refueled with clean fuel. Motor ran flawless! So I will be looking for a new fuel tank that's only about 9 to 12 gallons. I ran the mixture on a portable tank. The hard thing will be finding one that can actually fit my fuel port I have now. Issues with fuel are fixed.

You must not be fishing enough. Go to the lake more often and call it motor maintenance.
Glad to hear you got it fixed.

[gatorglenn]

You must not be fishing enough. Go to the lake more often and call it motor maintenance.
Glad to hear you got it fixed.

I have been trying. But between the motor issues, and my wife that feels a house we built 15 years ago. All of a sudden needs everything renovated. It's been tough getting time on the water. But I am fishing the rest of the fall.