Leaking fuel inlet

Discussion in 'The Venerable Q-Jet' started by rkammer, Aug 28, 2020.

  1. rkammer

    rkammer Gold Level Contributor

    The filter inlet of my QJ is dripping fuel and I've tried tightening it as much as I dare. It's a 1970 GS455 carb 7040240. When I removed the housing it had two gaskets on it so I tried reinstalling it with just one gasket and it still leaks. Is there a way to fix this? The filter housing looks pretty new and the threads look OK.
    Am I right that this is the correct early housing with the gasket behind the threads as opposed to the later housing with the gasket at the end of the threads near the carb?

    IMG_5735.jpg IMG_5736.jpg IMG_5737.jpg
  2. Cliff R

    Cliff R Well-Known Member

    Check the underside of the carb to make sure it isn't cracked or split back some. I see a lot of 1970 Buick carburetors with that issue for some reason.

    Remove the gaskets and check alignment of the fuel filter housing to the sealing surface. It may be off slightly allowing it to leak with only one gasket in place.

    There are several ways to make a repair if the heli-coil is off slightly or sealing surface has imperfections. Difficult if not impossible to make a repair if the casting is split or cracked......Cliff
  3. rkammer

    rkammer Gold Level Contributor

    Thanks, Cliff. I'll check that out. How about the thick, fiber gasket offered by several carb parts dealers? I ordered several in hopes that it may seal better? Can I add some gasket sealing compound to help the seal?
  4. BadBrad

    BadBrad Got 4-speed?

    The number one reason I've been running the same fuel filter in there since 1993!
  5. Cliff R

    Cliff R Well-Known Member

    Dangerous business messing with thick gaskets on the pressurized side of the fuel system.

    When a heli-coil is installed on the 1971 and earlier carburetors you loose some sealing surface. Tightening the fuel filter housing makes it want to push the gasket inside the housing right to start with and when the alignment is off some and they leak you end up torqueing them down even tighter. The metal coated gasket becomes the better part to use there but the correct fix is to resurface the sealing surface so it's in line with the fuel filter housing for even clamping force and a tight seal.

    Those thicker fiber or plastic gaskets can "relax" and develop a leak when driving and are not recommended. NEVER use any type of sealing on the threads either as it will find it's way into the carb and cause issues. Teflon tape is the worst and a lot of carbs end up here because folks used in on the fuel filter housing threads and it "snaked" it's way inside the carb........Cliff
  6. rkammer

    rkammer Gold Level Contributor

    Thanks, Cliff. Yesterday I tried again to stop the leak. I tightened the filter housing more than I thought was prudent and I think i have it stopped. I'll run it through a few heat cycles before I declare it fixed. I did put in a Mercury mesh filter and hope never having to remove it again. Fingers crossed.
  7. Cliff R

    Cliff R Well-Known Member

    You can torque it down pretty hard when there is a heli-coil installed however it will "pull" thru the factory fiber type gaskets and start to leak again.

    I like to use the metal coated gaskets when a heli-coil has been installed as they don't crush down and try to pull up inside the housing.

    PS: I also noticed that the carb is missing the front vent and someone blocked off the vacuum port on the front of the carb for the vacuum advance.
  8. rkammer

    rkammer Gold Level Contributor

    Thanks, Cliff. Yes, I had the vacuum ports blocked while I power timed it. I'll be removing both the TCS relay and the Thermal advance sensor and going straight to the vacuum canister with manifold vacuum. I have the vacuum canister that has the adjusting allen screw inside the port. I'll be tuning that next.
  9. Cliff R

    Cliff R Well-Known Member

    Good plan with the vacuum to the distributor. None of that stuff was worth two squirts of duck poop WAY back when they installed it. Everyone I knew yanked all that 1970 spark control stuff off before they had the car a week. Makes those items a bit difficult to find today, but even when I set up a car that uses it I put steel balls in all the lines and sneak a vacuum hose directly from the carb to the distributor so it works like it's supposed to.......
    rkammer likes this.
  10. rkammer

    rkammer Gold Level Contributor

    Isn't old school great! :D
  11. BuickV8Mike

    BuickV8Mike SD Buick Fan

    Looks like the Heli-coil is in there deep. The threads on the fitting are not really full sized there. I wonder if you could back it out a bit.
  12. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    The later Q-jets with the internal seal are so much better. Glad mine is a 72.

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