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Recently my 1972 Honda CB 450 has started leaking gas a good bit out of this left side nipple, it seems to be leaking a drop a second. I have the switch set to stop from the three options of stop, on and res so that shouldn’t be the problem, anyone know what the problem is?
65625
 

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That's the overflow drain for the float bowl. It could be two things: 1: the fuel valve doesn't really shut off in STOP, and needs rebuilding. 2: the brass tube inside the bowl is cracked, and it is slowly draining the bowl - it should stop eventually if the fuel valve is working.

BTW, this site wants an introduction for new members here: Motorcycle Forum
 

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I don't know your carbs, but:

You probably want to check the needle valve. If they are leaking gas into the float bowls, then the gas could come out of the overflow nipple. Or the gas could flow into the cylinder, and thus into the crankcase and dilute your oil.

Diluted oil does not lubricate well. A tap on the float bowl are with a plastic hammer or wooden stick may re-seat the needle valve. Don't use a steel wrench to tap or it might cause a spark/explosion

Stay well.
 

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If the main fuel valve is really off, the float valve is not involved, but if the fuel valve leaks, then the float valve is supposed to step up. Two failures, and the float overflows and, if the overflow can't keep up (usually not), fuel will also run into the cylinder, so check for gas smell in the oil, and the oil level rising. But, it is also common for that brass tube to crack, and letting the carb leak down until empty.
 

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^^^^^^^^
Very true. Pull the fuel line off the petcock, or where it connects to the carb.
Petcock set to off, should be no fuel dripping out. If so, bad petcock. Or lever in wrong position.

Either way, the float bowl should come off. Float valve should stop petrol regardless of petcock.
Heck, might be parts of the petcock, there's usually a small screen, degrading and messing both things up.

My bikes, every one has one of those lawnmower in-line fuel filters you can get at Lowe's.
Clear plastic, you can see what, if anything, is coming out of the tank. 8 bucks, cut the fuel line where you can see it real easy. Much luck partner.
 

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My bikes, every one has one of those lawnmower in-line fuel filters you can get at Lowe's.
Clear plastic, you can see what, if anything, is coming out of the tank. 8 bucks, cut the fuel line where you can see it real easy. Much luck partner.
Thing is, this bike has two fuel lines from the petcock, one to each carb, and the one on the RH side has no room for a filter; there is precious little room for on in the LH line. The valve outlet is shared equally, so the open line test is valid. Since the bowl needs to come off, anyway, no need to open a line, just remove the bowl. From there, you can test the float valve, too, by carefully lifting the float until it presses the valve needle into the body. Fuel should stop flowing when the bottom of the float is 20mm from the carb body, at the seal surface, with the seal out.
 

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Ya I'm with u on the room thing. Even tho my bikes only have one petcock, feeding 4 carbs, it's so tight
I have to remove the rear tank bolt first. Then, lift the back of the tank, I run out of fuel line slack at maybe 5 inches max, reach under by feel, loosen the screw clamp on the filter, and then the tank comes off.

Oh the joys of motorcycle mechanics.
 

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At least you can lift the back of your tank without fully draining it. The CB450 has a crossover fuel line between the two sides of the tank at the back, which passes under the frame. You have to reach up between the carbs and pull that line (which then needs replacing).
 

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At least you can lift the back of your tank without fully draining it. The CB450 has a crossover fuel line between the two sides of the tank at the back, which passes under the frame. You have to reach up between the carbs and pull that line (which then needs replacing).
Holy crap.

I thought about that with my bike. How the fuel gets from one side to the other. I guess the fuel sloshing around gets the fuel over the hump.

Could you get like a 12 inch piece of fuel line, and loop it over the frame, tape it to the underside of the tank?
 

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Could you get like a 12 inch piece of fuel line, and loop it over the frame, tape it to the underside of the tank?
Won't work; the fuel will be trapped on one side, as it would not cross the high spot. Most tanks are very close to even at the back of the tunnel, but the tunnel in the 450 tank is four inches deep, all the way at the back, and is only somewhat above the frame at that point.. So I don't have to replace the line every time, I added a self-sealing disconnect; still have to drain the tank dry, though.
 
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