Snapping noise

I recently spent some effort resealing the gaskets between the intake manifolds and the heads, and then ensuring that the nuts are unlikely to loosen again.  That made a major difference in how smoothly the car idled, cruised, and decelerated.  They are a royal pain to get to, but you might want to check those nuts as a vacuum leak there could possibly cause the symptoms you're seeing.

 

Gordon Nichols - Does his description sound like what you experienced?  You're the one who clued me in to this.

Todd, 57s are actually 57.5, I guess not enough room and/or tooling expense to label them that way.

 

Spray carb cleaner at the base of the manifold. If idle speed changes or poppping goes away, you found an intake leak.

Danny, would the carb cleaner spray also detect, in the same way, an intake leak between the mating of the carb to the top of the manifold?

Yup.

Todd.... Do I understand correctly that you replaced the 57s with the original 55s and the problem went away????     If so, you may have a 57 jet thats mislabled or has an obstruction in it.....   Maybe it wasn't seated properly in its holder....   Just passing thoughts...

That is correct...issue went away when i went back to .55 (which are larger than the .52 that came in the car).  I haf to adjust those as well but the actual snapping moise went away.  On the plus side withthe allen head holders incan change things out in a matter of seconds.  I am going check for
Leaks first and then might try the .57 again making sure about the seating properly.

When you use the aerosol carb cleaner, have the engine running at idle and protect the top of the carbs from getting any of the overspray.  The idea is the carb cleaner will make the engine 'stumble' and if it does, it will direct you to where you have an intake air leak. 

And if you've never used carb cleaner to find an intake leak, simply direct the spray (I use 1 second blasts at intervals so I don't end up soaking it with spray) along the gasket between the head and intake manifold, or between the intake manifold and the carburetor base.  As the spray passes a leak, the vacuum will suck some spray in making it temporarily rich in that intake and the engine will change idle note (stumble).  You don't have to drown it in spray for this to work, just short blasts and you don't have to be right on the gasket seam - within an inch or two of the gasket is fine.

 

If you don't notice any change, that's OK - it means you don't have any leaks and you can report back and we'll try some other ideas to help you out.

 

Oh, and it pretty much doesn't matter which brand of cleaner you get.  I personally like Gumout because it cleans things nicely, but no-name brand would work just as well.