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Discussion Starter #1
I had a closer look, and it seems that the cover for the secondary diaphragm is warped, so it isn't sitting flat against the carb. and therefore not creating a seal on the diaphragm. Basically when the cover is bolted on I can actually see a gap through the assembly. Unless my logic is way off base, without a seal, I get no vacuum, and without a vacuum, I get nothing.

I think I'll try to just make a custom gasket rather than attempt to un-warp the cover and see where that leads. I assume there is something in the guts of the carb. that would allow the vacuum to release?
 

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Any speed shop that carries Holley parts should be able to supply a new cap. If it is warped enough to see through, you will probably not get a gasket to seal it either.

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You've got a 4100, yes? It is odd that the cover is warped...

Is it possible to pull the cover and check it on a flat plate (like a surface plate)...even a piece of CR steel would work....if the cover is warped to a minor degree, you can flatten it by wrapping the same plate with a sheet of emery cloth or sandpaper and rubbing the cover on it...the same might be possible on the carb body as well....just be careful about the debris.

The vacuum in the pod is induced by airflow past an orifice in the primary venturi....once that airflow subsides, so does the induced vacuum, which then closes the secondaries...usually, theres a check ball in the vacuum circuit to slow the closing and opening of the secondaries so they don't slam shut when you get off the throttle....or slam open when the primary airflow reaches the critical point....

Does your vacuum pod have a spring which the diaphragm works against?

Pat
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Yes, it does have a spring which attaches to the cover plate, and it is a 4100 series carb. One concern with regards to sanding the cover plate is that there is a ridge on the surface that I assume is there to press into the diaphragm to help attain the seal, and if I sand it this ridge will be the first thing to go. I'll try the gasket, and if it doesn't work, I think I may have to find another cover plate somewhere.
 
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Warping is not uncommon. I bought a replacement cap from Pony carbs. If you sand it you'll wear out the ridge which is supposed to be there.
Good Luck!
 

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If you have a 4100, you can check the seal for the secondary diaphragm by removing the top of the carb, stroking the diaphragm and placing you finger over the supply hole near the top. (It is described in the ford shop manual)

I love 4100's,..the best carburator ever made!

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