Leaky Holley Main Body (porosity?)

[mopowers]

I've developed a leak in my old Holley 4779 750 DP. It's disappointing because this thing runs really well.

Any idea what could've caused this? I've had it apart several times recently trying to figure this out, but can't seem to nail it down. It's to the point where if the car sits for over a week without running, the primary bowl will drain completely.

I'm thinking it just be seeping from the main body like a porosity issue or something. Have any of you experienced this before?

 

[340doc]

The pictures wont open for me but I'm assuming you don't see any fuel outside the carb. Safe to assume you've replaced all gaskets and the power valve?

 

[yellow rose]

I can't see the pictures either but IIRC there is something called zinc lice or something like that. Without seeing the pictures, it's hard to tell.

Doesn't really matter anyway. If the main body is used up its time to buy a Proform main body and be done with it. There is no zinc in those if that is the issue you are having.

It's simply bolt your parts onto that main body and go. Plus you will have changeable main and idle air bleeds and while its apart you can drill and tap it for T slot restricters and really clean up the tune up.

 

[mopowers]

Thanks guys. The pictures should work now.

The pictures wont open for me but I'm assuming you don't see any fuel outside the carb. Safe to assume you've replaced all gaskets and the power valve?

The fuel is all on the outside. Should've mentioned that from the start.

I can't see the pictures either but IIRC there is something called zinc lice or something like that. Without seeing the pictures, it's hard to tell.

Doesn't really matter anyway. If the main body is used up its time to buy a Proform main body and be done with it. There is no zinc in those if that is the issue you are having.

It's simply bolt your parts onto that main body and go. Plus you will have changeable main and idle air bleeds and while its apart you can drill and tap it for T slot restricters and really clean up the tune up.

That's likely the next step.

 

[340doc]

Wow, that's unusual. Yep, time for a new main body like YR suggested. Looks like a nice carb.

 

[Mattax]

Looks to me like whoever converted it to 4 corner idle broke through when making the connecting passage. If you really need full four corner idle, then its better to start with a casting with more meat there. A -2 might have it whereas a -4 may not. You'll have to study them to know. Can't help further on that main body. I think I have a 4779 but like yours the choke horn is cut off so the revision is unknown.

 

[mopowers]

Looks to me like whoever converted it to 4 corner idle broke through when making the connecting passage. If you really need full four corner idle, then its better to start with a casting with more meat there. A -2 might have it whereas a -4 may not. You'll have to study them to know. Can't help further on that main body. I think I have a 4779 but like yours the choke horn is cut off so the revision is unknown.

Thanks- Interesting thought! It's a really old carb. My uncle had run it on an old race car of his back in the early 70's. I thought the drilling of the idle fuel passages were for the secondary side. This leak is on the primary side. But I'll definitely check.

I don't need 4-corner idle for my little motor, but it's what I had. Looks like proform main bodies are pretty reasonable priced too, so I'll probably just go that route if I can't locate another 4779 body for cheap.

 

[Mattax]

Thanks- Interesting thought! It's a really old carb. My uncle had run it on an old race car of his back in the early 70's. I thought the drilling of the idle fuel passages were for the secondary side. This leak is on the primary side. But I'll definitely check.

I don't need 4-corner idle for my little motor, but it's what I had. Looks like proform main bodies are pretty reasonable priced too, so I'll probably just go that route if I can't locate another 4779 body for cheap.

You're right. I'm wrong. That is the primary side. And I even looked at the choke tower being cut off. duh.
Hard to tell, but in the close up it looks like it may be wet in the dark recess further above.

Take it apart and look. You have nothing to lose. Clean and pick around the outside for a divet or crack.
Heck it could be a block gasket and thats why its hard to find.
With the engine off, the bowl fuel is on the other side of the metering block.
So lets think about where there are connections:
Main well the idle well connection is visible to the gasket.
Power valve cavity if the PV is not sealed (either diaphram or gasket) can leak downward.
Anything else?
on bottom of course is the accel pumps.
other?

ignore the emulsion tube -

 

[mopowers]

You're right. I'm wrong. That is the primary side. And I even looked at the choke tower being cut off. duh.
Hard to tell, but in the close up it looks like it may be wet in the dark recess further above.

Take it apart and look. You have nothing to lose. Clean and pick around the outside for a divet or crack.
Heck it could be a block gasket and thats why its hard to find.
With the engine off, the bowl fuel is on the other side of the metering block.
So lets think about where there are connections:
Main well the idle well connection is visible to the gasket.
Power valve cavity if the PV is not sealed (either diaphram or gasket) can leak downward.
Anything else?
on bottom of course is the accel pumps.
other?

View attachment 1715228621
ignore the emulsion tube -

Did some more digging. Turns out there's a tiny crack on the outside of the lower fuel bowl threads. Fuel is leaking through those fuel bowl threads. I can probably repair it with some epoxy, and maybe a helicoil but the main body is basically trash.