Diaphram torn in secondaries vacuum on Pony Autolite

There is no connection between the vacuum secondary diaphram and passages and the fuel distribution circuit on your 4100. Are you sure that your father didn't mistakenly remove the accelerator pump diaphram which is on the opposite end on the carb housing from the secondary diaphram?

The rubber sec. diaphram can deteriorate and harden over time by dry rot. An old diaphram may have been installed from the beginning. Dry rot is the same thing that causes tires to show cracks in the side walls. This will cause it to split. Sometimes a diaphram can be ruptured when one or more of the cover screws grabs the diaphram when the cover is being installed. This problem can be prevented by coating the screw's threads with some silicone grease.

The reason for using silicone grease is that it won't rot the rubber like a petroleum based grease such as Vasoline. The silicone grease is the same as what is used for disc brake caliper lubrication at the points where the caliper slides. It is available in small pouches usually found at check out counters at auto part stores.

You need to double check which diaphram it is that has the split. As I see it, there's no way that fuel makes contact with the sec. diaphram in any way. I'm surprised that the Pony Carb. people didn't mention this to you, but then again this company has had customers less than pleased with them in the past.

I will double check it this weekend myself. My father is a little busy with a new baby and the end of his lobstering season. But as for Pony Carburetors, I told them everything that I put here and they didn't say a word. They just said they would send me a new diaphram free of charge, and I was talking to the main tech guy, John (I think).

The secondaries haven't worked from the beginning and I just want to get it working as soon as possible. If this doesn't fix it then I am going to have to buy a new carb unfortunately.

As I said before, the Pony Carb people aren't that great when it comes to dealing with customers. The tech support in particular, so it doesn't surprise me that he didn't mention anything about fuel being behind the sec. diaphram. You are lucky that they answered the phone. A friend of mine tried to get in contact with a real person and all that he kept getting was an answering machine. The messages that he left were never returned. I don't know if this has been remedied. Maybe it has.

I still maintain that you won't find any fuel behind this diaphram. One thing that needs checking is if the ball check is missing in the vacuum passage to the diaphram. The passage is at the top of the sec. dia. mounting flange and is installed before the diaphram, return spring and the cover is placed into position.

A return spring that is too heavy will prevent the secondaries from opening when they should. Holley's return springs work on the 4100. The springs are available in a kit that contains several color coded springs that give different opening rates. You may need to go with a lighter spring to get the secondaries to work at the rate that's correct for your engine.

If you do decide to get another carb., Summit is now offering a carb that is very similar to the Autolite 4100. Many Holley parts fit these carbs. The 600 CFM vacuum secondary with electric choke sells for only $250. I bought one and found the quality to be very good. These are brand new carbs, not rebuilds.

On the customer service thing. Their response to me in May was the first response since I started last September.

I will check it out this weekend. Would the Ford Shop Manual have a good diagram of the carb? I have a manual but it is with my car at my father's where I stored it for the Winter.

Also. What would be too big of a carb for the engine? And, the carb you are talking about, is it a Summit brand carb? What do you think of Holleys and Edelbrocks?

I would like to say thanks for you help and advice.

tbunker said:

Would the Ford Shop Manual have a good diagram of the carb?

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Yes, the Ford manual has decent diagrams and descriptions of all the carb internals and how they work.

I have never dealt with Pony Carbs so I have no comment about them.

I agree there isn't any rational way for fuel to get into the secondary diaphragm unless possibly the secondary float level is so high that fuel is getting into the vacuum passage which runs through the carb top plate. Though if that were happening you would have other rich running problems.

To operate, the 4100 secondary has a finger sticking down into one, sometimes both, of the primary venturis as a vacuum pickup. From that finger the vacuum passage runs horizontally from near the vertical air cleaner bolt through the top plate, and down into the diaphragm body at the back of the 4100. There are a couple of holes in the top, main, bowl gasket that have to be open and properly aligned before any vacuum can make it to the rear. I think it is physically possible to put that gasket on upside down which will block at least one of those holes. The secondary diaphragm itself also has a small hole at the top that has to align and that one was iffy on my 4100 as well. Check to make sure none of those possible obstructions to the vacuum are causing your problem. Also, the diaphragm has a finger on the front, hidden side, that has to engage the plastic actuating arm or obviously it can't open anything.

The ball, if you have one, in the rear, angled vacuum passage at the secondary diaphragm is more likely to cause problems when closing the secondaries than when opening them. The ball is to slow the secondary throttle closing rate although it would slow the opening as well. Originally that passage had a small hole and a check ball which was spring loaded against the hole by a small spring and retainer. This caused engine over speeding on quick deceleration so the hole was enlarged and the spring and its retainer were eliminated in mid-1964. Many, I would say most, of the 4100s today don't even have that ball since it works nearly the same with, or without it. You get a similar check ball for the accelerator pump in any rebuild kit. The secondary ball is so (un)important that its not in any rebuild kit I have ever seen.

Ivy66GT said:

I agree there isn't any rational way for fuel to get into the secondary diaphragm unless possibly the secondary float level is so high that fuel is getting into the vacuum passage which runs through the carb top plate. Though if that were happening you would have other rich running problems.

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What do you mean by "rich running problems"?? Was that a sarcastic or a serious comment? I am only wondering because there are other operating issues associated with this carb at the moment other than just the secondaries.

tbunker said:

What do you mean by "rich running problems"?? Was that a sarcastic or a serious comment?

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Nothing sarcastic about it. If the rear float bowl is overflowing (which is one of the few ways I can imagine fuel getting into the secondary diaphragm) it could put fuel just about everywhere including into the vacuum passage to the secondary diaphragm which picks up its vacuum at the top edge of the float bowls by the center bolt. Once fuel gets into a vacuum passage it will be sucked into the intake manifold which is where vacuum comes from to begin with. That unmetered fuel will cause a rich mixture problem.

Since your secondaries don't open, such an overflow wouldn't have any affect on mixture from them but could be flooding fuel into the engine anyhow.

You seem to have multiple problems. Even without secondaries the carb should work much like a 2100. If its not even doing that you need to talk to Pony about more than one problem.

I have talked to them about the multiple problems but they keep saying that everything is related to timing. There is a rich smell while running even though we have the carb set a little on the lean side but not wanting to get really lean so that the car doesn't run even worse.

We put a cam, headers, and electronic ignition on when the car was still a 2BBL and it work great but as soon as that 4BBL went on, the car hasn't work the same. The timing has been set from one end right to the other end without making things better. It is now set to where it works the best.

Oh yeah! About half the gaskets are not sitting properly after more closely examining it. Some were poorly installed and some were poorly made.

The gasket for the secondaries diaphram chamber was so poorly made that it only covered half way over the screws on one side. Im sure that must have created some issues vacuum wise. Also the stall pot crumpled apart when we went to adjust it. I am going to get a spring kit for the secondaries and install a softer spring.