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  1. #1

    Fuel Pressure on OEM carbs....

    Im having problems establishing enough fuel pressure to run this triple piped 1390. What is most fuel pressure anyone has obtained with the stock setup??
    Not sure what is happening but I cant get it where I want it. 5-5.5 is the most I can obtain. Any help would be appreciated.


  2. #2
    spdracr's Avatar
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    Did you drill a 1/8 inch hole inside the carbs? Also, what size is your return jet? I'm using a 110 on my 1390 and my pressure is 6-7.

  3. #3

    pressure

    I have blocked the return jet off completely and can only obtain 5.5. Sometimes only 4 pounds. Very eratic!!! And I have a good liquid filled gauge.
    No pressure at idle, you have to burp the throttle to get the gauge to move.

  4. #4
    Moderator OsideBill's Avatar
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    I have to assume you have gone through and verified all the check valves are good in all the fuel pumps and that there are no leaks in your pulse lines. and that you have checked fuel filters. is the flapper and screen removed from the sending unit?

    are you running single or dual fuel feed?

    what else might be in your system that you did not mention fuel vapor seperator?

  5. #5
    Hydrotoys's Avatar
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    ONE of the three fuel pumps has a crease in the plastic check valves, or pump itself would be my first guess.

    Return and Supply lines backwards would be a guess too.

  6. #6
    spdracr's Avatar
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    The gauge should be tied into your return line not your feed line. Also on stock carbs you have to remove the fuel pumps and drill a 1/8 hole on the return for each carb. You can then use a 1/4 brass T and tap one end for a main jet (100, 105, 110, ect) for your return the top of the t should go to the gauge and the front back to your tank.

  7. #7
    spdracr's Avatar
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    Quote Originally Posted by OutlawGPR View Post
    I have blocked the return jet off completely and can only obtain 5.5. Sometimes only 4 pounds. Very eratic!!! And I have a good liquid filled gauge.
    No pressure at idle, you have to burp the throttle to get the gauge to move.

    The return jet should be facing the tank.

    Have you drilled the carbs out?
    They have a internal small hole on each carb.
    Last edited by spdracr; 04-22-2007 at 06:38 PM.

  8. #8

    pressure

    I have drilled the outlet holes to 1/8 inch on each carb. I do have the guage on the return side of the carbs. The lines are not crossed and I have removed the screen from the pickup.

    I went through the carbs when I drilled the returns and didnt find anything out of the norm. But obviously something is not right with the pumps. Is there a way to bypass the fuel pump on the carbs and use Mikuni High flow pumps. I was thinking that the checkvalve and diaphram could be remove from each carb but maybe Im wrong....

  9. #9
    Moderator OsideBill's Avatar
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    is the gauge between the carbs and the restrictor?

  10. #10
    Quote Originally Posted by osidebill View Post
    is the gauge between the carbs and the restrictor?
    Yes

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