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Yamaha XS750 Brake Rebuild

This is a discussion on Yamaha XS750 Brake Rebuild within the Technical forums, part of the Caferacer.net Forums category; Quick question ... my petcocks are shot ... should I rebuild them or replace them with something like this: YAMAHA XS400 XS650 XJ700 MAXIM XS750 ...

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Thread: Yamaha XS750 Brake Rebuild

  1. #21
    Member FranklinMarquette's Avatar
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    Quick question ... my petcocks are shot ... should I rebuild them or replace them with something like this:

    YAMAHA XS400 XS650 XJ700 MAXIM XS750 XS850 XJ900 SECA KZ750 PINGEL PETCOCK

    Also I'm replacing my rectifier with a modern one. I found two ... slightly different pricing ... just wondering which is the best buy. Neither has much for a description and they look exactly the same.

    http://www.madhornets.com/regulator-...ymEaArGa8P8HAQ

    http://www.electrosport.com/yamaha-x...rectifier.html

    Thanks!
    Last edited by FranklinMarquette; 04-20-2017 at 02:28 PM.

  2. #22
    jcw
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    Senior Member jcw's Avatar
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    Replace the petcock or rebuild without vacuum. The vacuum operated oem ones have been know to leak filling the crankcase with gas. Not necessarily the petcocks' fault...

    I have read too many bad reviews of Chinese reg/rec bad out of box.

    I've had one from Oregon motorsports that has been trouble free. More expensive but made in America. Not sure if you are US based.
    Last edited by jcw; 04-20-2017 at 03:38 PM.

  3. #23
    Member FranklinMarquette's Avatar
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    Just ordered one from Oregon motorsports ... I'm in the USA and would prefer american made.

    Okay what was the point of the vacuum of everybody changes it to manual?? Is the above linked petcock a good replacement?

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  5. #24
    Senior Member 8ball's Avatar
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    The point of the vacuum operated petcocks was, in theory, to make the operation of the petcock "automatic". It was to prevent someone from forgetting to turn off the petcock when they parked their bike, and having fuel drain out on the ground in the event that a float needle failed to seal properly. The vacuum from a running engine acts on a diaphragm that opens the fuel passage. There are two problems with this theory:

    1. A bike does not produce much vacuum when it isn't running, so you have to turn the petcock to "Prime" before you start it, to fill the carbs up. Then you have to turn it back to "On". Kinda negates the whole "automatic operation" thingy.
    2. (And this was more critical) The diaphragms have a tendency to leak after time, and this allows fuel to leak down the vacuum line. And instead of draining out the carb overflow....presumably onto the ground......it drains right down an intake port into the engine.

    Consequently, much like the Anti-stop, (oops.I mean, Anti-DIVE, front forks).....which were, too slowly, found to act contrary to beneficial fork action during trail braking....they were ditched long before fuel injection came on the horizon.
    Last edited by 8ball; 04-20-2017 at 06:48 PM.
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  6. #25
    Senior Member hillsy's Avatar
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    Quote Originally Posted by 8ball View Post

    1. A bike does not produce much vacuum when it isn't running, so you have to turn the petcock to "Prime" before you start it, to fill the carbs up. Then you have to turn it back to "On". Kinda negates the whole "automatic operation" thingy.
    You would only need to switch the tap to prime if the bike has been sitting for a few weeks or longer - if the bike is started / run every week or so there will still be enough fuel in the bowls to fire it up.

  7. #26
    Member FranklinMarquette's Avatar
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    Okay makes sense ... does anybody know of a good manual petcock replacement? I saw Mike's XS sells one for the 650 ... will that fit?

    Also I found out today that my Yamaha XS750SE is quite different than a standard. The front calipers and forks are drastically different for example. What else is not similar?

    My speedo gear drive is seized ... how does one go about taking it apart ... my Clymer manual skips over that whole are (and many others)

    Are there any other better, more detailed, manuals out there? I don't have the original one unfortunately.

  8. #27
    Senior Member hillsy's Avatar
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    Pingel sell fuel taps that are great quality - but they can be pricey.

    Easiest way is to measure the bolt spacing on your current tap and then find a manual one with the same spacing on eBay. Most taps are 34 or 44mm bolt space and a lot of bikes will use the same (think dirt bikes).

  9. #28
    Member FranklinMarquette's Avatar
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  10. #29
    Senior Member hillsy's Avatar
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    Looks like you have a 44mm spaced tap....which is a shame because brand new 34mm ones on eBay are under $10......

  11. #30
    Senior Member steveo's Avatar
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    I'd just buy some rebuild kits, certainly the cheapest option.
    It's possible to convert your existing taps to manual, a bit of faffing involved though........Yamaha Triples :: Vacuum To Manual Conversion
    "You were only supposed to blow the bloody doors off"

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