'84 SECONDARY FUEL TANK

[benny220]

I was trying to get my fuel delivery system working correctly this weekend. I had problems with with my '84 vf500c carbs not getting fuel. I temporarily bypassed the fuel filter to see if that was my problem. When everything was connected, I started the bike and ran it for a few minutes, then I realized the secondary fuel tank was leaking. I'm not sure what happended there, as there had been fuel in the secondary tank before with out a leak.

My question is, can I bypass the secondary tank and just gravity feed the carbs from the primary fuel tank?

[Charles S Otwell]

Did you check your fuel pump or disconnect it before you started it?

[dgc67]

My question is, can I bypass the secondary tank and just gravity feed the carbs from the primary fuel tank?

Interesting.  I would think you probably can, but it will take some creative engineering.  the fuel line, at least on a VF700, from the upper tank to the lower tank is like a 1 inch line.  You will have to come up with a way to reduce it down.  I THINK the only reason for the fuel pump is because it cannot be gravity fed due to the fuel line out of the second tank being so low.
If you do try this PLEASE post your results.

[benny220]

On the primary tank, there is a large opening(about 3/4" to 1") then there is a second opening, maybe 3/16"-1/4". I was thinking of closing off the large opening, and using the secondary to fed the carbs. The only problem is there would be no fuel shut off.

To answer a previous question, I'm pretty sure the fuel pump was hooked up. It seemed like the leaking fuel was coming from the tank itself.

[dgc67]

On mine, the 2nd, smaller, hose is a vent line only.

[benny220]

Ahh, that may not work well then. I was thinking of maybe sealing off the large diameter fuel opening in the primary tank, and attaching a fuel shut of to the primary tank. Let me ask this question. Would gravity feeding the carbs produce too much fuel, to the point where the fuel will run continuously out the overflow lines? Does anybody know if there is a difference in the mechanics to feeding the carbs by gravity and feeding the carbs by a fuel pump? Are there differences between petcocks, or seals, etc.? What causes a gravity feed system to stop the fuel flow when the bike is not running?

[cluke3]

thats right the small tube is the vent

[dgc67]

Would gravity feeding the carbs produce too much fuel, to the point where the fuel will run continuously out the overflow lines?

As long as the fuel pressure from a gravity feed is not higher than the fuel pump pressure, and I doubt it would be, then it should be fine.  I would be more concerned with not enough fuel supply at WOT.

What causes a gravity feed system to stop the fuel flow when the bike is not running?

the petcock and/or the needle valves (1 in each carb)