quawk
2nd Gear
Posts: 150
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Post by quawk on Jan 21, 2022 17:19:34 GMT -5
I am probably missing something obvious or that has been covered before but what is the function/purpose of the hose to the rear of the fuel petcock? I'm talking about the short hose that connects to the rear of the petcock and runs up to the tank. What is the hose connected to inside the tank? I have recently had my petcock removed and did the blanking modification of the vacuum circuit, and have capped the vacuum supply tube but don't see the purpose of this hose/supply that I speak of to the petcock.
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Post by wayne on Jan 21, 2022 17:43:22 GMT -5
It's a breather. The pipe it connects to in the fuel tank is a long metal tube that curls up into the top of the tank (ie sitting mostly above fuel level).
Precisely what it's venting I've forgotten, I'd have to look at the petcock closely again.
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quawk
2nd Gear
Posts: 150
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Post by quawk on Jan 21, 2022 18:43:28 GMT -5
So I have my tank off of the bike, empty, sitting on the bench. If this hose is a vent, if disconnected at the petcock but the other end of the hose still connected on the tank end, should I be able to blow through the hose and air should pass freely into the tank? It does so with the cap off, but if I reinstall the cap, you can blow air into the tank, but will pressurize the tank and will return out the hose once you stop blowing. Is this a possible cap vent problem?
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Post by hudson on Jan 22, 2022 11:02:30 GMT -5
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Post by wayne on Jan 23, 2022 1:29:43 GMT -5
Quawk you should not be able to pressurize the tank by blowing into the hose. I checked mine by sucking on it using a vacuum pump and gauge. It will not allow even the hint of negative pressure as the cap must be venting.
It would be worth checking your cap vent as well as following up Brian's info.
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quawk
2nd Gear
Posts: 150
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Post by quawk on Jan 25, 2022 12:09:09 GMT -5
About cap venting, shouldn't you be able to pull at least a very small amount of air through the tank with your vacuum pump if the cap is indeed venting to atmosphere. How can you check the gas cap for proper venting? It seems you ought to be able to figure out how they vent by looking it over closely, but have to admit I must be missing as to how it does.
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Post by wayne on Jan 25, 2022 16:08:17 GMT -5
I probably phrased it badly QUAWK. My vacuum pump was unable to achieve even a hint of vacuum because my tank was venting well. If the cap was blocked, the pump would have started to create low pressure in the tank. Going back to your earlier post you said you could blow into the tank and it would pressurise until you released the breather hose. That sounds like your breather could be blocked.
Look under the chrome cap. There are small holes which you may need to check are clear.
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