2stroke1971

1985 RX7, 12A 5 speed.

My secondaries stopped working after rebuilding the carb. Trying to troubleshoot them down.
I pulled the carb again, the gasket beween the throttle body and mid section WAS installed correctly..(if backwards, it can block the vac port that helps supply the actuator.)

I did not replace the acuator diaphragm, as one did not come with my Hygrade kit, but it is supple, no holes, and it worked before.

Where the actuator mounts to the carb body, there is that one little port that supplies vacuum. I made sure that channel was clear, through the carb, where it meets up with that little brass jet in the throttle body (the one that gets blocked if the gasket is backwards)....made sure that little jet was clear as well.

Further tracing the path of vacuum for the actuator port, I noticed that there is also a channel cut into the bottom of the midsection of the carb, starting in the corner where the vacuum goes up to the actuator port,(and where that little brass jet is) This channel runs around to the center of the carb, to a large bore that I (think) leads into the venturi at some point, to add vacuum to the whole process I suppose, based on velocity coming don the throat.


The shaft that the secondaries operates on has a torsional spring in it....also with the throttle closed, there is a physical stop that limits the secondaries to a bare crack. As the throttle linkage moves, the secondary shaft is left at the mercy of that torsion spring, it will open, but must work against that spring. At the EXTREME end of the throttle linkage travel, there is a link arm that defeats the torsion spring and the secondary shaft moves freely, without effort. (of course this is with the carb in my lap, and no actuator hooked up)

So now my questions:
In normal operation (no mods) does the vacuum acuator defeat that torsion spring to open the secondaries, or can the secondaries ONLY open at that extreme throttle position where the torsion spring gets relieved by that link arm?

I would think that there would be many circumstances that would call for secondaries when the pedal is not stomped to the floor, right?

Also, I would think that at that extreme pedal position, that engine vacuum alone would be enough to suck the secondaries open, is that the function of that relief arm? (I bet that if I leave the atcuator arm that connects the secondary shaft to the actuator off that flooring the thing alone would let the secondaried get pulled open, but I certainly dont plan on that!)

IF the secondaries are ONLY supposed to open when the linkage is at the far end of it's travel, then maybe my throttle cable needs adjusting?!?

Also, I put a vacuum gauge on the actuator port before I pulled the carb, and with the car running and revving, there was no vacuum there. I have a work around in mind, if they are still not opening...I am going to modify the actuator so that I can hook a normal vac line to it, but I would need a way (most likely) to attenuate it in that case. If it gets to that, I will post about it and how it went.

Any comments or suggestions would be greatly appreciated.

Neil

LizardFC

iTrader: (1)

This is a tough one to visualize without pics, but I'll try to add what I can in hopes that something might help.

Have someone sit in the car (engine off) and floor the gas, or wedge a brick on it. Have a look at the primaries. If they aren't completely vertical, then you have too much slack in the cable. As long as the primary butterflies can fully open, then the secondaries should be able to as well. With the primaries open, try to turn the secondary shaft yourself. Make sure nothing is catching it, like the teeter totter or some other misplaced piece of linkage.

Those diaphragms get weak with age, so it may just not be opening enough. Not much you can do about it aside from going to mechanical secondaries. I highly recommend it. It simplifies the system, eliminates an inevitable failure, and it's even tunable if you're clever on how you tie the linkage together. I would at least twist tie it up as a test to see if you can feel any difference.

fastorlast

I have a question... How do you know the secondaries aren't opening? It was my understanding that the secondaries won't open without engine load ( ie wont open if in neutral and revving) so unless your driving around with someone sitting in the engine bay to see if there opening (NOT RECOMMENDING THIS) how are you sure there not opening?

2stroke1971

Just "feel" and sound. Before the rebuild, the exhaust note would change and you could feel it with the infamous "butt dyno" when they kicked in.....overall, acceleration is better/smoother after the rebuild, just no sick rush like before. Although I have to say I fixed some leaks in the exhaust since then as well so maybe im just not hearing the exhaust like before. I dunno. I cleaned up the base plate real good and put some new gaskets on it, gonna tighten up some more hose issues....

Thought about mechanical secondaries, but not sure...so the diaphragms are not to be had new huh? I think its a vac supply issue to the diapragm...
I am gonna put the carb back on this afternoon and we'll see what happens. I though about running it with the lid off the air cleaner so I can hear when the secondaries open better.

Can you fiddle with the mechanical secondary stuff with the carb on? Seems a bit crowded on the front side, is that where you have to wire it up?

Thanks,
Neil

LizardFC

iTrader: (1)

Yeah, you're not going to see much happening while free revving. Best way to test them is to cap off the vacuum to the box. Drive it around, give it a little hell. Hook it back up and note any difference. Not having them open at all makes a huge difference.

I'm not aware of any source for the vacuum diaphragms. I know they don't come in the GP Sorensen kit. Where are you pulling your vacuum signal from?

You'll want to pull the carb to do the mechanical secondaries mod. The easiest place to rig it up is on the back side.

2stroke1971

Well, I took the plunge so to speak, and hooked up mechanical secondaries. I did it on the backside, I drilled very small holes through the levers and used two passes of safety wire to bind it up. Works nice, I am installing the carb tonight, we'll see by tomorrow I bet.

Thanks again everyone, I will let you all know!
Neil

LizardFC

iTrader: (1)

Good luck! You'll probably like it. One thing you can do is "tune" at what point the secondaries open by using shorter or longer ties and modifying the linkage. I've experimented a bit with mine and found that I like them to begin opening at about 1/2 throttle. This pretty much ensures that they stay shut during normal driving and helps with mileage a bit. I'm planning on tuning that a bit when the turbo setup is done, as I'll want them opening really early to deliver extra fuel as boost pressure builds.

fastorlast

Or you can do it the things the sterling way and mod the little piece of linkage that's attached to the secondaries throttle shaft on the firewall side of the carb

2stroke1971

After driving it, I have found out that my secondaries were INDEED working before I rigged the mechanicals. With all the vacuum problems and the exhaust leaks buttoned up, the whole thing is much quieter than before the carb rebuild, I guess thats what I was not hearing it.

Also, I figure, before the carb rebuild, with the rotten accel pump and all, the acceleration was a bit lethargic so the diffference I was feeling when the secondaries kicked in seemed greater, more of a light switch effect so to speak.

Now, with the mechanicals, the only drawback I see is that if you try to mash the pedal at certain times, you do get that cough. What I have found though is that this only happens if you give it the secondaries before it would normally be calling for them.

In other words, at low rpms, chugging in 2nd gear, if you mash it it coughs briefly.
If you are more gradual on the pedal there is no hesitation as the secondaries open.
If you let the rpms build, and then mash the pedal, then no hesitation.
In first, if you mash it off the line, no hesitation because 1st is geared so low I guess.
Not sure if I will leave it this way. I can certainly drive it so that it never coughs, and with normal driving, they wont come on much, so Im not worried about fuel economy.

I will leave it up to my son, whose car this is, whether to leave them as mechanicals. He's 19, and this is his first car. He got it cheap but needing alot of TLC. I work cheap, and I have to say I fell in love with the car when I drove it home after buying it. The payments for my services are test drives.

Seriously, I need to get one of my own. Thanks again everyone!

LizardFC

iTrader: (1)

Glad you got it figured out. You can all but eliminate the "cough" by modifying the accel pump. There are three basic steps:

Increase the capacity by boring out the inside or adding extra gaskets as spacers.

Hogging out the jet and the nozzles.

Adjusting the linkage to change the duration of the "squirt."

Although like you said, you can learn to drive around it. Which may be the best thing for a young driver. It'll teach him the proper technique to driving these cars, which is to not romp on the gas, but ease onto it, and to keep it in the powerband under heavy throttle. Not that he's going to be racing around in it, of course

Quel

I apologize for this being off subject a little, but this could help me answer a question without starting a new thread.

Is that "cough" a normal phenomenon with normal vacuum secondaries? If I romp on my accel when it's in neutral, warmed up, and at 750 idle; it will kill the engine. Thank you so much for any reply.

LizardFC

iTrader: (1)

I wouldn't call it "normal," but I would call it "typical." It's a failure of the accelerator pump, which is supposed to deliver a direct shot of gas into the airstream as the throttle is pressed. I would say either there is a clog in the system or the diaphragm in the accel pump housing has worn out. It should come with any rebuild kit and is pretty easy to replace.

RGHTBrainDesign

Mine was fixed with a fuel cleaner and hard driving. Try moving the pump by hand and making sure that piston slides easily, that's half the battle. Of course, if the diaphram is bad, it will need rebuilt.

LizardFC

iTrader: (1)

+1. Sometimes Seafoam will work a miracle. Also a little WD-40 on the linkage can help keep it from binding up due to gunk and corrosion. Might as well try the simple fixes before you go tearing it all apart.

Quel

Thanks for answering my offtopic question, it is sticking; I got it running better again.

RGHTBrainDesign

Yeah mine was not only sticking, but leaking at the rod, probably making it stick in the first place. Time to pick up a carb rebuild kit.