On the intake manifold, smack dab in the middle of the picture, the orange plastic piece with the U shaped vac hose. The plastic nipple broke of and now I don't remember where it connects to. What the heck is that?

If that is left open, can that cause my idle to jump around? A picture showing where it connects to would be great.

 

That's the altitude compensator. It connects to a large hoze nipple right next to the mix screw, like this:



Since it bypasses air around the throttle plates, it could make fora very large or very unstable vacuum leak, depending on how it broke off.

 

Wrongo! The altitude compensator is up on the carb itself. Sterling took one apart once to see how it works. Kind of a neat little device.

The part the OP is talking about is a PCV valve on his '79-'80 manifold. It pulls vacuum from both primary runners at idle so it needs to be blocked off or fixed and routed correctly. My old school engines have it mainly running to the oil filling tube. This prevents the margerine and water you get condensing under the oil cap.

To the OP, the plastic in normally a natural nylon type color. Yours is old discolored and brittle. An easy fix is to break the rest of the plastic off the metal part, remove the little spring and valve assembly inside, find a piece of hose (1/2" or 5/8", can't remember), zip tie it on the metal part (nipple) and hook the other end of the hose to an aftermarket PCV valve like a Fram FV333 or similar inline style. Run the other end to your oil fill tube nipple (this is an 8mm or 5/16" size so get a smaller hose).

 

I'm sorry, Jeff, but you are incorrect. The SAs do not have a discrete PCV valve; they use the Ventilation and Check Valve which mounts to the rear of the rat's nest to perform the same function that a PCV does.



The part indicated in the OP is the Altitude Compensator, part # 8761-13-770, connects to the carb using hose 8871-13-775.



Clearer pic of it without the carb in the way here:



Schematic:





The older-style Altitude Compensators were a bellows-type setup, multiple hoses; the 79 RX-7's started using the simpler one, and the Vent and Check Valve for vapor control. Maybe they re-used the same hole in the manifold that the older PCVs went to? I don't know - - never had an old-school car.

 

Ah, then that's where the confusion came from. Thanks.

 

you know, you guys are alright! thumbs up to Jeff and Glen for outstanding and thorough information! glad that was cleared up properly. and i learned something today about the SA!

 

Great info, that's exactly what I'm looking for. Thank you. Without plugging/routing it, I was able to tune my idle at around 750rpm. Not too bad. I'm sure once I correct it I can dial it in better.

Now I drove it around the block today and my temp rose and my "add coolant" warning light came on. I just put in a new thermostat and coolant is flowing but the temp keeps rising to an uncomfortable level. I am completely confused. This is my last problem to figure out.

 

You've probably got some trapped air in the system. Common problem after changing t-stat or otherwise draining some coolant. Baby may just need burping, heh.

Did the t-stat you used have the "jiggle pin" in it, and did you put it at the top when you installed it?

 

I have no idea what the "jiggle pin" is. I took the old t stat out and the new one went right in. I also put some "radiator Drain-o" in the system and it's all good now. I must have had a blockage. A new thermostat never hurts though haha

 

The original rotary t-stats had a small hole in one part of the valve flange, with a little pin valve in it that was meant to let air burp past the t-stat rather than get trapped behind the flange when the t-stat is closed.

The little valve wasn't spring loaded (water flow closed it) so it would jiggle around when you shook the t-stat.

So, "jiggle pin." Still considered by many to be the earmark of the best t-stat for a rotary. But it only works if it's at the top when installed.

Pic:

 

Ha, I'll have to take mine out now and take a look

 

Hi, my little plastic nipple just broke off for the ac valve. I live in Hawaii at 0 altitude, should i just eliminate this all together? Thnks

 

If you plugged both openings you would probably be all right. Possibly would have to re-tune your idle some.

If you stay below 3000', you won't notice an appreciable RPM change based on the FSM data. But don't some of the islands have some pretty sizeable mountains on them?? I remember Haleakala topping out at like 10,000 feet.

 

yeah, I stripped this part living in Miami, but considering to put it back on because I want to take the rx7 cross states!

 

I think you would be safer eating off Glen's engine than a Denny's Table (Definitely Cleaner!) I'm so jealous hehe

 

Don't try it after a car show... too much fresh drool!