rx7haze

I recently rebuilt the carb and stripped it (mostly) and removed the rat's nest on my '80. It idles fine and runs great and throttle response is great. But I don't think my secondaries are opening and I can't figure out why. If I manually open the throttle and manipulate the secondary diaphragm linkage, the secondaries will open all the way. The diaphragm is in good shape. I don't think I have a vacuum leak because everything else seems to be fine. When I'm driving if I push the pedal to the floor I get no additional response for the last 1/3 or more of pedal travel. Am I missing something obvious? I would like to keep the vacuum operated secondaries, the mechanical conversion doesn't appeal to me for the way I drive the car, but I would like that last bit of power back. Before I rebuilt the carb and removed the rat's nest I could very distinctly feel the secondaries open, although not that powerful because things were gunked up. But I could feel that extra oomph.

Jeezus

iTrader: (4)

Before you rebuilt the carb?

I assume you missed this part:

https://www.rx7club.com/showthread.p...ht=secondaries

Kentetsu

Definitely worth checking the "teeter totter". Very common problem, which is easily solved.

rx7haze

The teeter totter is definitely hooked up. I came across that thread in my search and double checked before posting.
I'm assuming that by being able to operate the linkages manually and getting the secondaries to fully open, that I don't have a linkage issue.
Is there any way to verify that the diaphragm is actually moving the linkage?
Is it possible that something is blocking the vacuum to the diaphragm?

Kentetsu

You could apply vacuum to the diaphragm and watch it operate. If it works as it should, then my next guess would be clogged jets in the carb. Check it out, and post back with the results and we can go from there.



.

rx7haze

How do I apply vacuum to the diaphragm?

DivinDriver

iTrader: (15)

Hand-held vacuum pump is the easiest way. Pretty inexpensive tool, and quite handy.

Kentetsu

You might be able to generate enough vacuum just by sucking on the hose.

Otherwise, you could probably find any vacuum source and re-route the hose to it temporarily just to verify if the system is working. However, you will have to be sure that the source you use is actually generating vacuum at idle (some do not).

rx7haze

I'm getting a little confused so please bear with me. The secondary gets its vacuum by being attached directly to the carb body. There is no hose coming to this component. Is the idea here to remove the secondary from the side of the carb then attach a vacuum source to it?

Kentetsu

Okay, it's been a while since I've seen a stock carb, but from what I remember there was a vacuum hose attached to the mechanism. Can someone verify this?

Another alternative to consider would be the mechanical secondaries mod. This will replace the vacuum assembly with a simple piece of wire to operate them. The instructions for this can be found in the FAQ section. I did this with my old carb, before I got the Sterling, and it worked very well.

DivinDriver

iTrader: (15)

On the '80 carb, the secondary diaphragm bolts directly to the side of the throttle body, and connects to vacuum via a gasketted port with no hose.

Testing the diaphragm with with a hand pump requires removing it from the carb, and using a cone adaptor on the pump. Only way I know of to definitively test the diaphragm, unless you can watch it open while the engine's running.

Sterling

The vacuum diaphragm is attached to the main body, you mean.

There is a tiny port in the side of the primary venturi on the vacuum box side of the carb. Though the other venturis have this port drilled at their apexes (...apexi ??), the vacuum signal that acts on the diaphragm comes only from that one primary venturi.
If you can operate the secondary shaft (ie, move the vacuum box diaphragm lever), you should be able to feel / hear the air coming out of that orifice (with the engine off, of course...).

Didja check your throttle cable?

rx7haze

"If you can operate the secondary shaft (ie, move the vacuum box diaphragm lever), you should be able to feel / hear the air coming out of that orifice (with the engine off, of course...)."

This checks out.

I did check and adjust the throttle cable such that the butterflies are wide open when the pedal is at the floor.

I now have a question about the secondaries in general. Am I supposed to feel them kick in or is it supposed to be a smooth transition? Is it possible that my secondaries are working correctly but I'm having a problem somewhere else? I'm pretty sure I'm not getting all the power I should be. Not sure where to look next.

Sterling

No, not necessarily, especially with an auto tranny.
Assuming you have a manual, @ what RPM are you shifting?
Fuel starvation issues generally show up at 5500 RPM as an inability to climb much higher than that without going lean.
If you can take her to 80 in 3rd gear, your secondaries are working.

74RX4

iTrader: (10)

Did you separate the throttle body from the main body? If so did you get the new gasket on right?

Secondary diaphragm vacuum source



Secondary diaphragm passage



Throttle body to main body gasket

WRONG



RIGHT

This guy

well ****... 12 years later and I have this problem... by any chance, if ofcourse you do see this, did you fix it or find out how?

Carl

iTrader: (2)

As 74RX4 pointed out (apparently with photos that are no longer visible) if you get the gasket between the main body and throttle body in backwards (pretty easy to do) the vacuum signal will not get to the secondary TV actuator. You will probably also have a vacuum leak. You might be able to screw it up with the gasket between the air horn and main body also. Check those both to make sure the gaskets are in right and not covering any holes.

This guy

I figured it out, thankfully I put the carb back together properly but however I didn't realize the previous owners didn't and they hadnt hooked up the second half of the throttle cable on the other side of the carb... the car runs amazingly now that I have the full pedals worth of movement 🤣