What valve is this on a stock 12A intake manifold?
 

I'm cleaning up a stock 12A intake manifold, and I have this valve that threads in just below the carb spacer on the primaries' side. My valve had what appeared to be a yellowed, broken plastic nipple coming off of it. Seeing as it was broken, I hacked off the plastic to see how it worked--so I need a new one. What is it, and where to get it?

Thanks,

why would you want to replace it? It has to do with emissions, many have said when you take it out it smooths out the cars idle since that dumb thing just flops around in there anyways... I took mine out and i think it made a little difference, mmmmm better air/fuel flow is always a good thing

Well, the plastic nipple thingy I hacked off was what held a spring and plug inside the valve. As the plastic nipple is unusable at this point, I'd need a new one just to plug the hole. It's a big hole, so I don't know if finding some other threaded object with the same diameter would be a good option.

Besides, I like to know what the hell things are, regardless of whether or not I'm going to cap it.

I think Dan S Young was referring to the "butterfly valve", but I'm not sure that is what you are talking about. "Butterfly valve" and "plastic nipple thingy" sounds like two different things....?

The butterfly inside the primary barrel, and the valve that actuates it collectively are known as the "shutter valve assembly".

The shutter valve is a relatively useless emissions control and anti-backfire device that never really does anything useful and usually gets stuck after so many years of use.

Leave the butterfly in the manifold (removing it creates turbulance, bad thing), but remove the associated valve. Anything actuating it on the outside of the intake manifold goes. Removing the two bolts on the firewall side of the manifold and the circlip that holds the valve to the arm of the butterfly allows you to remove it. Once it's removed you have to plug the holes in the side of the intake manifold or you'll get a massive vacuum leak. I used JBQuick Weld for that, worked really well. I applied two coats to make sure I got it good and sealed. Then you have to stick the butterfly in the "open" position so that it will allow the most air possible to flow around it. I also used JBWeld for this.

Basically by having the plastic cap broken off you're probably causing a vacuum leak. The full valve is available as a one-piece replacement from Mazdatrix and they even have an instruction page, but it's not worth it. It's BLOODY expensive to do.

Jon

I removed the butterfly as well and noticed a considerable increase of power at high rpms. My butterfly was closing when flooring it!

Mine flopped around also as it was not stuck and was disconnected from the vacuum line. After removing it I have noticed a slightly better idle (smoother) and am overall happy with the results. I thought turbulent air broke up the air fuel mixture more as to get a more efficient burn.... Could be wrong. Dont know too much about the exact subject.

Having never driven mine before it came out I can't say what "difference" I noticed, but I can tell you one thing:

I have no anti-afterburn valves, or shutter valve, and I still don't backfire!

Jon

Same here. It takes a real effort to get the car to backfire. Even with headers, no cats, no AAV, etc.

It is your muffler cdrad. You need a straight through type for best flame-throwerability.

I rather keep my RB muffler and not have to explain cops why my car is throwing flames :p:

Hmm. This is not how I pictured the butterfly valve. Also, this is supposed to be a '79 manifold. Time for a picture or two, I suppose.

The caption in the manifold pic describes what it looks like it does mechanically. I thought the butterfly valve shut off mixture to the the rear rotor during deceleration for fuel economy and early rotor failure, which is not what this appears to do.

Thanks,

-dave

Bumpity bump bump, bumpity bump bump, look at this thread go...

I believe that is an altitude compensator, it's a 79-80 thing. Take it to the hardware store and match it to a pipe-thread plug, then cap off the hole in your manifold. Use some gasoline-safe thread sealant, and cap off wherever that hose leads also (sorry, I don't recall where it goes).

Nimrod, you rock sir. Thanks for the answer. As for what attaches to the valve, it doesn't matter as this is not the one in my engine bay--it's going to be mated with a rebuilt '79 Nikki and swapped in.

Thanks,

-dave