Carb issues

Discussion in 'The Venerable Q-Jet' started by hgiljr, May 24, 2020.

  1. hgiljr

    hgiljr Well-Known Member

    We never took the carb off while he was here. I will discuss with him. I know he wanted to have the new fuel line and correct PCV valve in to continue tuning. His goal was to do basic tuning to confirm there would be no detonation and then do step 2. Thanks for info.
     
    12lives likes this.
  2. Cliff R

    Cliff R Well-Known Member

    "The epoxy is to seal the plugs, which often leak. That's SOP for most all rebuilders, I'm sure Cliff and Ken both do that."

    "Dabbing" epoxy, especially JB Weld over leaking bottom plugs is completely USELESS.

    100 percent of the carbs that come in here repaired in that manner will leak right thru that "monkey-chit"!

    The only effective repair is to remove the plugs and tap the casting for screw in plugs, then coat the set screws to be installed with a fuel grade epoxy. That is what I do here, and all the folks dabbing JB Weld over leaking plugs just cost me an extra half hour or so of time removing all that crap.......FWIW......Cliff
     
    Last edited: Jun 4, 2020
  3. 12lives

    12lives Control the controllable, let the rest go

    But it would not affect the air bleeds or contribute to the problem the OP is having, right? That why I asked.
     
  4. TORQUED455

    TORQUED455 Well-Known Member

    Leaking well plugs can cause a rich mixture, especially at idle, but the 2 most prominent symptoms of leaking well plugs are a hard hot-soak restart (too much fuel) and long crank after days of sitting (bowl empty). I agree with Cliff - the old JB Weld is the Edsel of epoxies and should not be used anywhere near fuel. Ironically, another “old” epoxy works just fine around fuel (Marine Tex). Maybe there are others.
     
    Brett Slater likes this.
  5. Cliff R

    Cliff R Well-Known Member

    I'd add here that leaking FRONT plugs (the ones under the jets) go straight into the intake. Since they are exposed to engine vacuum fuel can be "pulled" out of them and cause idle and running issues.

    Early Q-jets used lead plugs in the front and brass "cup" plugs in the rear. The leak rate for the brass cup plugs is 100 percent. I've never seen a Q-jet that used them that didn't leak back there.

    The lead plugs will leak about 30 to 40 percent of the time. The later swaged in aluminum plugs seldom leak front or rear, but EVERYONE dabs some monkey chit over them in futile attempts to seal them up.

    Marine Tex works well for sealing things up IF you tap the casting for screw in plugs.

    JB Weld is absolutely USELESS as mentioned and even when the repair looks good and before the glue gets "soft" it will fail a high pressure test 100 percent of the time.

    It's interesting here as I pressure test every single carb I work on it's it EXTREMELY rare to see a post 1975 carb leaking anyplace. I can't remember too many that were, and to date haven't had a single Marine carb post 1978 ever show a leak anyplace.

    As it relates to this topic my advice is to pressure test FIRST, then make repairs if/as needed. If you don't see a leak after 50 something years then the carb is probably good to go for another 50 years or so and I'd leave things alone in that area........FWIW......Cliff
     
  6. Cliff R, where is a good place to get a rebuilt quadrajet? I see quite a few companies but I have no idea who actually does a solid job and doesn't cut corners.
     
  7. LARRY70GS

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

    techg8 likes this.
  8. LARRY70GS

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

  9. I just ordered a carb from him. It'll be nice to have the Wildcat be leak free and reliable.
     

Share This Page