Porosity; Carb Porosity

[jocko463]

Hey Guys,

I'm a new forum member.

I have a copy of Cliff's book "How to Rebuild and Modify Rochester Quadrajet Carburetors". I've been poring over it and learning the in's and out's of the Q-jet and how adaptable/tunable it is. If you haven't gotten a copy of it, I highly recommend it.

In choosing a carb to work with, the book says that older carbs from the 60's are shunned for a few reasons but one of them is because of casting porosity. Unfortunately the subject of porosity is not really talked about ....other than the fact older carbs are more prone to porosity. I know what porosity is but the question is: How do you determine if the castings of a carb are too porous?

Additionally, what are tell-tale signs, if any, to look for? Is there anything that can be done to restore or eliminate excessive porosity in an older carb? Since the book shows some pre-75 carbs, I can assume that one can use the older versions ....say a late sixties carb ....for a rebuild-able core.

So what's the scoop on porosity?

Thanks,

Mike

[omaha]

usually if a carb has porosity, it will be visible at least from what I have seen. Not many have that bad of porosity from my experience. If i remember right, the "Carter" made ones had some problems a little. Just one that I have taken apart has had porosity.  I thought one I had might leak so I left it sit overnight with some gas in it (outside of course and covered). It did not have one bit leak through, no stains even.
I guess if you found one with bad, highly visible porosity, it would be best to avoid using it for a rebuild. I can think of no 100% effective way to fix it. I wouldnt worry too much. (unless it is some high dollar resto with a rare carb on it). I dont think it matters from old to newer versions. I think the older ones had more lead in them (from what I have heard on this forum)  Jus my .02 worth. BTW, I did a ford 1 barrel for a guy and it had a ton of porosity in it. Had to get another carb and start over.

[Cliff Ruggles]

The first thing to look at is thread "erossion" at the fuel filter housing and fuel inlet seat.  Look for heavy pitting, and even cracking or failures in the bottom of the bowl of the main casting.

Some castings will simply have seen more use, and more exposure to the elements.  I see some that are in perfect shape nonetheless.  Most will have some warpage and pitting from oxidation, inside and outside.  We leak and pressure test all of them.

In any case, I see a LOT of early carbs with problems with the castings, and ALL of them will leak at the bottom plugs prior to 1969.....Cliff