1981 Yamaha fuel flow from tank

[cgtech]

Perhaps a fuel.line has collapsed internally, plugging the line. You have not said if you were, or were not able to blow air through, only that no fuel will come out.

[Prof100]

Originally Posted by cgtech

Perhaps a fuel.line has collapsed internally, plugging the line. You have not said if you were, or were not able to blow air through, only that no fuel will come out.

I can pressurize the tank but fuel will not exit the tank through the fuel out line.

I took the tank out of the system and I filled the fuel filter then cranked it over. No fuel was drawn from the filter. Go figure.

[slonomo]

It should be an free ride from the tank to the fuel pump, as far as restrictions go. The only thing in the lines between them is a fuel filter.

Try this:
1. Remove the supply line at the fuel pump. Blow air through it back to the tank. If you get bubbles in the fuel tank, you have no restrictions. If you don't get bubbles, you have a collapsed fuel line.
2. Also, if there is any crack or damage to that fuel pickup hose it will not suck any fuel.
3. You could try the reverse and suck fuel manually with a vacuum pump, that would be more accurate.
4. You could manually put a vacuum to the pulse line on the fuel pump to see if it will pump fuel. I usually use a clean fuel hose and use my mouth. It won't get fuel in your mouth, it's just the vacuum line.
5. Sometimes the vacuum action will pull a worn out rubber line closed, collapsing it. You might think about replacing the rubber lines.

Fuel Pump
The fuel pump does need vacuum pressure from the engine. It's called a "pulse pump", meaning it needs a vacuum pulse to operate the diaphragm in the pump, that's what will pump the fuel. The pump literally sucks fuel from the tank, then pumps it to the carb.

The factory Mikuni pump is a nice unit, and can be cleaned and rebuilt, if you can find the parts. Not sure if they are available anymore?

It's the same type of pump you'll find on most tractors and riding mowers etc that use a carb, with the exception of gravity feed models. On my G1 I replaced the old factory worn out fuel pump with a Briggs and Stratton unit, worked great.

[Prof100]

Originally Posted by slonomo

It should be an free ride from the tank to the fuel pump, as far as restrictions go. The only thing in the lines between them is a fuel filter.

Try this:
1. Remove the supply line at the fuel pump. Blow air through it back to the tank. If you get bubbles in the fuel tank, you have no restrictions. If you don't get bubbles, you have a collapsed fuel line.
2. Also, if there is any crack or damage to that fuel pickup hose it will not suck any fuel.
3. You could try the reverse and suck fuel manually with a vacuum pump, that would be more accurate.
4. You could manually put a vacuum to the pulse line on the fuel pump to see if it will pump fuel. I usually use a clean fuel hose and use my mouth. It won't get fuel in your mouth, it's just the vacuum line.
5. Sometimes the vacuum action will pull a worn out rubber line closed, collapsing it. You might think about replacing the rubber lines.

Fuel Pump
The fuel pump does need vacuum pressure from the engine. It's called a "pulse pump", meaning it needs a vacuum pulse to operate the diaphragm in the pump, that's what will pump the fuel. The pump literally sucks fuel from the tank, then pumps it to the carb.

The factory Mikuni pump is a nice unit, and can be cleaned and rebuilt, if you can find the parts. Not sure if they are available anymore?

It's the same type of pump you'll find on most tractors and riding mowers etc that use a carb, with the exception of gravity feed models. On my G1 I replaced the old factory worn out fuel pump with a Briggs and Stratton unit, worked great.

Let me digest your thoughtful response. Which Briggs pump did you use?

[Prof100]

Is this the pump? A new G1 pump is $100+. Rebuild kits are not available.

https://www.amazon.com/Stens-520-590...dDbGljaz10cnVl

[slonomo]

Originally Posted by Prof100

Which Briggs pump did you use?

Um....the one in the pics I always use genuine Briggs parts. The China aftermarket stuff is junk.

[Prof100]

Originally Posted by slonomo

Um....the one in the pics

Thanks. Did you notice the description states not compatible with 10% ethanol fuel.

[slonomo]

Originally Posted by Prof100

Thanks. Did you notice the description states not compatible with ethanol fuel.

It says "not greater than 10% Ethanol". Most fuels in the summer blends are E10 fuel.

I also use fuel stabilizers in my fuel for equipment, golf carts, 4 wheelers etc. It makes the ethanol safe to use.

Most of the issue with ethanol in fuel is that it swells the rubber seals/parts and it corrodes metal. This additive takes care of that. E15 in the winter is even ok if you use the additive. Never use anything more than E15.

[Prof100]

Originally Posted by slonomo

It says "not greater than 10% Ethanol". Most fuels in the summer blends are E10 fuel.

I also use fuel stabilizers in my fuel for equipment, golf carts, 4 wheelers etc. It makes the ethanol safe to use.

Most of the issue with ethanol in fuel is that it swells the rubber seals/parts and it corrodes metal. This additive takes care of that. E15 in the winter is even ok if you use the additive. Never use anything more than E15.

I uuse Ethanol Shield. Works well.

[Prof100]

Update. I threw in the towel on this one and called in the Yamaha service center to take it into the shop.
Three major problems,
1. No fuel draw. (Original concern)
2. No spark. Just checked and I get no spark.
3. It looks like the oil seals may need replacing which would explain no fuel draw. Oil residue is evident. I replaced them once in my 25 years of ownership in the late 1990’s.

Three strikes and I give. Time to use the most powerful tool in my toolbox — my checkbook.