Air pipe flap actuator

Hello all and Happy New Year!!

I am wondering about the actuator for the flap situated inside the air filter pipe of a SII XJ6.

What exactly is the function of the flap and where can I find a replacement actuator?

The one I have must have a faulty membrane since it does not respond to vacuum.

Here are some photos of the item.

The vacuum flap servo is controlled by a small thermostatic switch between the carbs. When the engine is cold thr switch connects the inlet vacuum to the servo which pulls the flap closed against spring pressure. When closed, the flap makes the air filter breathe hot air from over the exhaust manifold, via thr tin shield and cross-over pipe.

This warms the engine quicker and keeps intake around 40c for the best jettingg and emmissiona. The thermostatic switch opens again when cold and If it breaks or a tube or servo leaks it all fails “open” so the car just warms up slower.


Thanks. What I expected only brilliantly explained!

This one is faulty. Where would I find a replacement? Or do I just toss the thing out and neutralize all connections?

Hey I have one I will check tomorrow see if it’s fine? Let me know if you want it I reside North of sunnyvale.??

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That’d be great !!! :slight_smile:

Yes I have 2 of them you got time to come to santa rosa?

I need to get organized for that. Wiél confirm. :slight_smile:

Ok hey question you have a series 3 xj with carbs think I’ve missed something isn’t your EFI ?

Ok you havery series 2 my bad! I have a series one xj it connects to a thermostatic valve which also goes bad. I bypassed all that it just for emissions no big deal just delete all that I think your dizzy vac line comes of that also has with my series 1 hook it to a port on carb do you have strombergs? I put HS8s on mine also I put series 3 dizzy in with amplifier works a treat points not so good there cheaply made in China these days! I have a really nice idle now set my timing 10 BTDC.

You are right. I am going to cancel all that stuff and keep it simple.

A main function of the set-up is to counter carb icing, Eric - but also to maintain constant carb air temp for more consistent mixture…

Ie, carbs are adjusted with the engine hot, and a constant air temp. The latter a finer point in fuel economy and consistent engine behaviour…

However, unless you frequently experience high humidity and freezing point - omitting the feature should make little difference…

xj6 85 Sov Europe (UK/NZ)

Thanks Frank, the South San Francisco Bay is notorious for it’s lack of humidity and cold weather so… :slight_smile:

I would prefer to find a working replacement part but that seems to be an vain quest…

A Polish guy called Artur on the E-Type UK forum is about to make his own servo function again, I think. A few dollars could fix yours mebbe? After all it can be left off and the vac tube blocked until well after the car is back on the road.

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Thanks Peter. Very interesting. I was looking into opening the thing you to fix it. It is one of the quirky gadgets that I like to get to work just out of challenge. :slight_smile: But opening this thing is a recipe for a big scar on the hand…

Given all else that needs to be done on the car, I will probably take a short cut on this one :slight_smile:

I have cut open several components, like this vacuum actuator, after they failed to see why they failed. It is usually due to a tear in a rubber diaphragm. To cut them open safely I place them in a vise and use my dremel with a cutting wheel to cut it open where the halves were connected. Note that these were destructive inspections to find out what failed and why as I didn’t plan to fix them or put them back together again. I do this to satisfy my natural curiousity of how things work and why they don’t work when they fail. I have a heater control valve on my work bench right now that I plan to cut open soon. It failed in the open position and would not close when vacuum was applied. A new replacement valve fixed the problem, but as always I am curious as to how it failed. It should only take a few minutes to do. Maybe I will cut it open this afternoon to satisfy my curiousity. :slight_smile:


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Eric. Looking at that actuator I would guess that it is an ac brand unit sourced from GM.and used in millions of their carbureted cars. Try visiting a boneyard and see if you can match it up with a good working part.

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You mean something like this?

That looks like the one. You would need to physically compare them to be sure. They were used for many years on many different gm cars so there may be some variation between applications but as long as the part physically fits it should do the job. It has been many years since I had my series 2 xj6 so memory is not that great but I seem to remember that the air cleaner plenum was stamped as an ac part. I would search for one that was used on the air cleaner as opposed to the heater box.

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Great and on the back plate of the air box is the bimetal switch for this diaphragm actuator: I removed it from the backplate and it is marked AC on the top :slight_smile: I will post a picture

Here is what the Repair Operation Manual says about this.