Vacuum leak?

Discussion in 'Small Block Tech' started by Golden Oldie 65, Jul 5, 2019.

  1. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    Ok, it's not a Buick but the basics are still the same. The son of a friend of mine has an old IH Scout, I'll guess late 60s-mid 70s with only around 42,000 original miles on it and actually in very clean original condition, even has the original paint on it. It ran great but leaked oil everywhere so he took it to a local mechanic for the fix. The guy pulled the engine and supposedly replaced all the gaskets and valve seals and put it back in. Now it runs like crap. The mechanic told him to rebuild the carburetor. Of course, he has no idea how to do that and asked me if I would do it for him, so today he pulled it off, I rebuilt it and put it back on for him. It's a Holley 2bbl., the original carburetor. The Scout has a V8, and 345? I don't know much about them but anyway..... As I suspected, rebuilding the carburetor didn't really help. It runs crappy and wants to die all the time, yet if I close the choke almost all the way while it's running it smoothes right out. I'm thinking maybe intake gaskets or some other vacuum leak somewhere. I looked at all the obvious places but found nothing out of the ordinary. Any suggestions? This is a freebee so I really don't want to spend a week working on it but I said I'd help so I'm stuck with it.
     
  2. 72gs4spd

    72gs4spd Well-Known Member

    Sure sounds like a vacuum leak. Check the obvious first, split hoses on fittings for one. If you have a gauge see what the idle vacuum is should be like 18 or higher. If you spray carburetor cleaner around gaskets for carburetor base, intake and hoses the idle will smooth out when you spray where the leak is. I knew an old timer that used a propane torch without the flame, not advisable. Good luck.
     
  3. Julian

    Julian Well-Known Member

    There's no such thing as a vacuum leak... Vacuum is only... Air leaks...
     
  4. alec296

    alec296 i need another buick

    Intake gasket, check timing and points. Maybe a crossed plug wire.
     
  5. Stevem

    Stevem Well-Known Member

    Closing the choke off and getting a better idle is a sign of either a vacuum leak or the Carb being too lean once the motor is up too temp.

    If the engine starts fine when cold just like it always has before the rebuild then I would say the poor idle issue lies in the Carb if all the vacuum hoses check out.

    Please note that I have had vacuum hoses that where cracked yet made no issue until the motor was hot , so check them real good!
    I have also had metal screw in vacuum fittings that where busted / cracked during a rebuild and once again did not leak until the motor was hot!

    Also I have had old grimy Carbs gummed up on the throttle shaft such that once rebuilt and all cleaned leaked tons of unneeded air thru a now clean worn throttle shaft Bore, so check that out also!
     
  6. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    I checked the plug wires/timing order and loosened the distributor and tried going a little each way and it only got worse. It was the end of the day and was all I had time for. I'll have to get back to it tomorrow or Monday. Just hoping someone would have some suggestions that I haven't thought of. I figured on spraying the carb cleaner around the intake gaskets. I've dealt with vacuum leaks before but never this bad. I mean, it doesn't smooth out until the choke is nearly fully closed.
     

Share This Page