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  1. #1

    J tubes in carbs

    I have seen some topics on J tubes in carbs latley and I have a Mercruiser with a 502 Rochester carb and I am afraid to take it out because it does not have a J tube in it and I don't want to be a bomb on the water. I checked several other boats and they did not have them either. Has mercruiser put us all in danger???

  2. #2
    Join Date
    Jan 2001
    ST. Louis, MO, USA
    J tubes are intended to dump the fuel down the carb throat if the float valve sticks open. The Qjets on boats cut their bowl vents at an angle so the gas will likewise flow down the carb instead of pouring all over in different directions. Look at a car Qjet. The bowl vent is cut strait across.
    Yours is fine if it has an angled cut.

  3. #3
    Join Date
    Dec 2000
    Flemington, N.J. U.S.A
    If you are in dought ,Get a short peice of fuel line and hook it beween the front and rear vent tubes like an arch .Figure out the center and cut 2 or 3 , 1/4"holes in the bottom of the hose centered over the carb opening .That way if it does spray fuel it will go through the hose and dump into the center of the carb .

    I had floats stick on me without this or J tubes and it left fuel all over the side of the carb and intake . It could have been bad !!

  4. #4
    thanks for the reply, but I have a rochester 4 barrel & it only has one vent tube & we hooked a fuel pump to the carb. in a tub & took the float out so we could see what really happens with 7 to 8 lbs fuel pressure & even with the angle cut on the tube we had fuel spraying all over the back of the carb. not down inside.

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