Wrong Carb gasket? (1 Viewer)

[Mark7640]

Chasing a vac leak at the base of my carb and realized I have a bolt with a hole thru the center on the base of my carb(pic) that holds the plate between the throttle body and carb base. I assume the hole is there for vacuum? But when I look at the insulator (pic) it appears this hole would be complete closed off. I know I have carb not original to this vehicle but curious what if any issues this may cause. Never seemed to be an issue for last five years. Recently had carb off to remove the air rail and noticed.

 

[Mark7640]

bump

 

[brian]

normal

 

[John McVicker]

^^^
Yep, normal. Look elsewhere for your vacuum leak.

 

[thebigredrocker]

Here's where the hollow bolt receives vacuum.

 

[brian]

you are planning to replace those garlock gasket(s) correct?

 

[Mark7640]

Here's where the hollow bolt receives vacuum.
View attachment 2319466

Ahh. Didn’t notice that. Thank you for clearing that up!

 

[Mark7640]

you are planning to replace those garlock gasket(s) correct?

So is that the green gasket I have in the second pic you refer too? Seemed like it was bonded on there and thought I had read somewhere not to mess with them? School me please. What would you replace them with because I believe that to be the source of my vac leak (at least one leakanyway). I noticed some carb cleaner liquid on there from sorry I got it around the base when testing for my leaks. Thanks

 

[thebigredrocker]

@Weber Sarge is a carb guru and has commented about the carb base insulator. At one time he mentioned he has the equipment to sand old insulators flat. Pretty sure he lives in your state.

When I installed the new Trollhole carb awhile back I used the stock insulator with the addition of two new 1/16" gaskets to seal the base up . Works well and addresses the insulator's hardened gaskets without having to try to remove them . The only sealant I know of may be The Right Stuff but doubt it's up to the temps of a dual manifold design if that's what you are running .
Sarge

 

[brian]

that's a replacement gasket...while it maybe glued on, it shouldn't be as they don't need to be.
SOR carries them, i'm sure other places do as well.
garlock shouldn't be reused a second time

 

[Mark7640]

that's a replacement gasket...while it maybe glued on, it shouldn't be as they don't need to be.
SOR carries them, i'm sure other places do as well.
garlock shouldn't be reused a second time

Gotcha. Thanks for clearing that up. I feel better about removing it now as I am pretty certain it was a source of my vac leak. Thanks again.

 

[brian]

if not that one, perhaps the one on the bottom side of the insulator.

 

[FJ40Jim]

That is the original gasket still bonded to the insulator block. It is quite re-usable. It is in excellent condition and is obviously not a source of vacuum leak.

Your 75-76 carb does not have the vacuum drilling to pass vacuum to the hollow screw. The vac passage the screw connects to is not drilled through at the top of the carb.

Spraying fuel at the carb base will give a false indication of vac leak as the fuel gets sucked in around the throttle shafts. The minor air leakage that occurs at the shafts is normal. These are not the vac leaks you are looking for.

Are you sure there is a vac leak? Or is the weak, erratic idle due to the too lean US-spec idle jetting?

 

[Mark7640]

That is the original gasket still bonded to the insulator block. It is quite re-usable. It is in excellent condition and is obviously not a source of vacuum leak.

Your 75-76 carb does not have the vacuum drilling to pass vacuum to the hollow screw. The vac passage the screw connects to is not drilled through at the top of the carb.

Spraying fuel at the carb base will give a false indication of vac leak as the fuel gets sucked in around the throttle shafts. The minor air leakage that occurs at the shafts is normal. These are not the vac leaks you are looking for.

Are you sure there is a vac leak? Or is the weak, erratic idle due to the too lean US-spec idle jetting?

Thanks Jim! I was kinda hoping it was the original bonded gasket. And your comment about spraying around the shaft makes perfect sense. It did change rpms significantly so maybe I am ok. I did find another small leak where the brake booster hose connects to the manifold and resolved that. So I am now idling reasonably smooth at 660-680 rpms with a hot engine and have a vacuum reading at 17-18. Can someone confirm that is a reasonable vacuum number?
Thanks everyone for the input.

 

[Pighead]

So I am now idling reasonably smooth at 660-680 rpms with a hot engine and have a vacuum reading at 17-18. Can someone confirm that is a reasonable vacuum number?
Thanks everyone for the input.

17-18 is an acceptable vacuum reading (What altitude are you at? Vacuum will decrease as altitude increases.)
FSM says 20-22 IIRC for a newish engine.
Maybe adjust valves just a smidge tighter, maybe advance timing a bit, see how that affects vacuum.
Otherwise, drive it.