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Thread: Fuel tank breather question.

  1. #1
    Join Date
    18.07.2018
    Location
    North Pennines
    Ducati models
    750 SS
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    6

    Default Fuel tank breather question.

    Just bought a '93 model 750SS and am now in the process of giving it a thorough checkover to familiarise myself with it and to look out for any gremlins before taking it out for my first ride on it.

    The first issue was the reg/rectifier, which wasn't connected to anything. I thought it was probably duff, and that the vendor had simply disconnected it so I wouldn't know, but having wired it up it seems okay. At least the charge light goes off when it's started up.

    The second thing that looks suspect is the fuel tank breather. According to the manual, the pipe that goes from the top of the fuel tank and into the top of the fork yoke is a breather pipe (as opposed to a vent pipe). However, on my bike, the aluminium one-way valve on this pipe is stamped with a little arrow pointing away from the tank. That would make it a vent, not a breather. So, am I right in thinking that the valve has been fitted the wrong way round, and the arrow should actually point towards the tank? Also, does the pipe simply end in the fork steerer or should it lead somewhere?

    Hopefully, someone here knows the answer.

  2. #2
    Join Date
    19.12.2005
    Location
    Forfar, Angus
    Ducati models
    Supersport 939, 907ie
    Other bikes
    Pantah 500SL, Scrambler Classic
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    8,487
    To make sure the battery is charging connect a multimeter across the battery. WIth the engine running you should be seeing around 14V across the battery.
    I can never remember which way round that breather should be but there is an easy way to find out. Blow through it. You should be able to blow easily in one direction but with difficulty in the other direction. Fit it so that the air can get easily into the tank. And yes, it just goes to the steering stem.

    Old enough to know better, young enough not to care

  3. #3
    Join Date
    18.07.2018
    Location
    North Pennines
    Ducati models
    750 SS
    Posts
    6
    So that tube coming out of the top of the tank is indeed a breather, as I thought. In which case, the one-way valve on my bike is the wrong way round! Easily sorted.

    Had I gone out on the bike before checking it over, I would have broken down after a few miles due to fuel starvation from the breather valve fitted incorrectly. That happened to me many years ago after fitting an alloy tank onto a Rocket Gold Star. The fuel cap lacked the necessary breather hole, so no air could get into the tank, causing fuel starvation. Took me quite a while to figure out the cause of the problem.

    As for the voltage regulator, I will check the voltage before taking the bike out for its first test run. Hopefully that will be tomorrow, weather permitting.

    Just had the rear tyre off the rim to clean off corrosion which was causing multiple air leaks. That's now back on the bike and holding air, so it's all ready to go. I'll be taking it very steady, having not ridden a motorcycle for a couple of decades...

    Many thanks for the advice, Derek. Much appreciated.

  4. #4
    Join Date
    18.07.2018
    Location
    North Pennines
    Ducati models
    750 SS
    Posts
    6
    Just double checked the breather valve and it was in fact fitted correctly. The arrow on the valve is the opposite way to the flow direction, hence the confusion.

  5. #5
    Join Date
    19.12.2005
    Location
    Forfar, Angus
    Ducati models
    Supersport 939, 907ie
    Other bikes
    Pantah 500SL, Scrambler Classic
    Posts
    8,487
    Quote Originally Posted by Wheelnut View Post
    Just double checked the breather valve and it was in fact fitted correctly. The arrow on the valve is the opposite way to the flow direction, hence the confusion.
    I think the arrow gets everybody confused with these things

    Old enough to know better, young enough not to care

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