Help with Holley carb leak, please!

[PeniroN]

Holley 850 vacuum secondary is leaking from what looks to be the bottom of the secondary bowl. I’ve replaced gaskets on the secondary metering block, bowl, and bowl screws. Still the same leak. I’ve looked for cracks and casting flaws, in the components and the only thing that looks off is a missing plug on top of the metering block in the center relief. See picture.

I’ve had this car for a few years and noticed a slight leak at the secondary last year. The fuel pump went bad over the winter and I replaced it with the same pump and that’s when I noticed the leak was much worse.

Does the hole in the metering block need to be plugged? Could that be causing the issue?

Thanks in advance!

 

[Murray]

I draw file all surfaces to be sure they are flat.

 

[George Jets]

For float bowl gaskets, dry installation of a new, high-quality gasket is the most reliable method.

In a pinch a very, very thin application of "Aviation Sealer" on both sides of the used gasket, paying attention that no excess squeezes out to get into the carb internals.


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[PeniroN]

I draw file all surfaces to be sure they are flat.

I’ll check the surfaces for flat this week. Thanks.

 

[RustyRatRod]

If you know someone with a dye penetrant kit, they can crack check it.

 

[PeniroN]

If you know someone with a dye penetrant kit, they can crack check it.

I think I found what’s causing the leak. I’m surprised I didn’t notice it before. I believe the spotfaces that seat the screw seals on the bowl are off center from the through holes. There is very little clearance (like 0.005”) from the through hole to the screw. Also the screw seal has the same clearance to the screw. So the offset spotfaces are preventing the screw seals from seating properly. I can actually see indentations in the plastic seals. What do you think? Sounds reasonable?

 

[RustyRatRod]

I think I found what’s causing the leak. I’m surprised I didn’t notice it before. I believe the spotfaces that seat the screw seals on the bowl are off center from the through holes. There is very little clearance (like 0.005”) from the through hole to the screw. Also the screw seal has the same clearance to the screw. So the offset spotfaces are preventing the screw seals from seating properly. I can actually see indentations in the plastic seals. What do you think? Sounds reasonable?

View attachment 1716565077

I don't know. I guess if you are using the hard Teflon seals, they might be kept from sealing, but the softer gaskets should conform to that.

 

[PeniroN]

I don't know. I guess if you are using the hard Teflon seals, they might be kept from sealing, but the softer gaskets should conform to that.

Yeah, they’re hard plastic.

 

[RustyRatRod]

Yeah, they’re hard plastic.

Use the soft gaskets and that should seal it.

 

[Sterling]

Make sure your power valve plug isn't hitting on the main body, and holding the metering block away. The little hole in the top of the metering block is for a small rivet, that holds the bowl vent.

 

[PeniroN]

Make sure your power valve plug isn't hitting on the main body, and holding the metering block away. The little hole in the top of the metering block is for a small rivet, that holds the bowl vent.

The primary side had the plastic channel that was held on with a rivet. Since this is the secondary side does it need the channel? It was not there when I disassembled. If it doesn’t need the channel do you think the small hole needs to be plugged? No power valve on the secondary metering block, but the plug does clear the main body.

 

[PeniroN]

I went ahead and had a machinist friend spotface the bowl screw seal seat concentric to the mounting holes. I’ll see if this helps seal tonight. Thanks for all the ideas!

 

[PeniroN]

Looks like the new spotfaces fixed the leak. Even with plastic washers. I went ahead and bought a set of soft washers just in case. Thanks for the help.

 

[RustyRatRod]

Looks like the new spotfaces fixed the leak. Even with plastic washers. I went ahead and bought a set of soft washers just in case. Thanks for the help.

Great. Glad you got it sorted out. Little crap like that can be frustrating.