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Leaking petcock and rebuit carbs

Discussion in 'XJ Technical Chat' started by Wendall79, Jun 30, 2007.

  1. Wendall79

    Wendall79 New Member

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    I finally confirmed that the petcock on my '81 xj650 is leaking. But - I just had the carbs cleaned/rebuilt by a bike shop. Sure enough - the oil level magically "raised" itself. Of course, I drained it and it came out practically thinner than water (I had 20w50 in there!) and reaking of gas.

    My question is: shouldn't the float valves in the carbs prevent the carbs from flooding and dumping the gas into the engine? Is it possible that the petcock could leak the gas into the vacum line? Or is it more likely the carbs are simply overwhelmed with all the extra gas when sitting?

    So, the gas line is staying disconnected until I figure what to do about the petcock valve (actually the whole bike isn't going anywhere until I get a new clutch cable, which broke while riding the other night - but that's a story for another post).

    Any recomendations about the petcock? I think I would like to get an aftermarket on-off valve.
     
  2. Nick

    Nick Member

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    The petcock is the first place to stop the fuel flow when the engine is not running. The second place is the float valves. You need both to fail to get fuel into the crankcase and both failures do happen.

    So, if the gas line is disconnected and you have fuel in the tank, is it leaking fuel out??? It should only flow fuel in the prime postition when the engine is not running. There are repair kits on the market for this valve, some have had success and some have complained. If you do a search on this site for petcock repair you should find other comments on the subject.

    Float valves do hang up, a gentle tap on the float bowl will usually jar them loose. If you replace them all with new ones there still is no guarantee that one of them will not hang in the future.

    Replacing the valve with an on/off valve is a sure fire way to get fuel shut off. Again do a search on this site and you will find some pictures of other members making the switch.
     
  3. BlueMaxim

    BlueMaxim Active Member

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    Yes. If the diaphraghm is ruptured it can leak back into the vacuum line. The vacuum is applied to the back of the diaphraghm to pull it back, dislodge the plunger and it's oring and allow fuel to flow. The diaphraghm being the seal between the fuel and the #3 intake vacuum line.
    I have often speculated that the float valves may be over worked trying to hold back the full pressure of a full tank of fuel. Don't know that they are but this is why I replaced my petcock last week with an on/off one.
     

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