ThirdPedalNirvana

The following pertains to my 1985 GSL with stock (California) emissions control, a.k.a. the "Rats Nest", which until yesterday I thought was complete.

While attempting to diagnose a problem which I thought was in the carburetor but now I'm led to believe is ignition (see my other thread), I noticed that a vacuum line was clearly disconnected over by the electropneumatic switches. I reconnected it and then followed it around to a pneumatic valve on the other side of the carburetor. A little research showed me that this is one of the two "Afterburner" valves.

The 1" hose from the afterburner valve to the air filter box is in place, however, there is no hose attached to the other 1" port. Based on what I've read, this valve is supposed to let air into the intake through a check valve under deceleration, but I cannot see (without major disassembly) where this hose would go, and I don't have the hose in the first place!

So connecting the vacuum line doesn't do any good or any harm, as it simply actuates a valve which is disconnected. However, I am not sure how this Afterburner system works, and how important it is? Can someone explain it?

Because a hose to the filter box isn't special, it essentially is atmospheric pressure air but filtered. The check valve, I presume, is sitting down where I can't see it and letting air into the intake from below the carb whenever there is sufficient engine vacuum, such as during deceleration. So then what the heck is the afterburner valve for?? I get why its better to pull air from the filter than from the engine bay, but why did Mazda bother with [electric signal] to [pneumatic signal] to [2-way valve]??? I presume there must be some circumstances under which the car does NOT want to allow air into the intake below the carb, even though there is sufficient vacuum to open the check valve. In that case, my car isn't operating right! However it's been driving fine (except for the very recent issue with hesitation which I think is ignition). Would a carb need to be retuned to function when this hose is missing, and would adding the hose make it run badly? Should I be trying to replace this hose? or was it the port likely blocked off by a previous owner?

tl;dr: I live in California and want a fully stock and emissions compliant 12A. My afterburner valve is not connected to the intake plenum. Should I care?

KansasCityREPU

iTrader: (9)

This might help. I haven't looked through this recently so I'm not sure if it talks about the rats nest.

https://drive.google.com/file/d/0Bzy...kMWVkMjZl/view

ThirdPedalNirvana

Thanks for the reference, but no it does not describe the afterburner valve, only the parts of the carburetor assembly and the function of the carburetor. I believe the afterburner valve allows air to bypass the carburetor.

Stripgear

iTrader: (2)

I believe you are referring to the shutter valve. See page 57 here:

http://foxed.ca/rx7manual/manuals/RE...amoto-1981.pdf

Toruki

I just read that book, from that link, it's really good. And by "read" I mean the words, not the reams of formulas with the derivatives and the calculus! Super interesting. I like the distinction between knocking and preignition which I always thought were the same thing, but not in the rotary engine at least.