Hey everyone, I’m working on my 1985 RX‑7 (FB, 12A, electronic ignition) and I’ve run into a strange issue with the Nikki carburetor. My vacuum advance hasn’t been working, so I went hunting for the ported‑vacuum nipple on the passenger side of the carb.

Here’s what I found:

• The location where the ported‑vacuum nipple should be had a threaded plug installed
  
• The plug had a hex base and a flat‑blade screwdriver slot
  
• It was sealed with some kind of rubbery sealant
  
• After removing the plug, the hole is completely blocked
  
• Spraying carb cleaner into the hole does not enter the primary bore
  
• It looks like the ported‑vacuum passage may not be drilled at all
  

So now I’m wondering:

1. Did a previous owner install a carb that doesn’t have a ported‑vacuum circuit?

2. Are there Nikki carb versions that came without ported vacuum?

3. Is this carb even compatible with the stock vacuum‑advance distributor?

4. Should I replace the carb (correct Nikki vs Holley 390 vs Weber)?

The car runs, but without vacuum advance it idles rough, runs hot, and has poor throttle response — all consistent with no ported vacuum.

Any advice on identifying this carb model, restoring the port (if possible), or choosing a replacement would be hugely appreciated. I can post photos if needed.

Thanks in advance!

 

Post some pics up of the base plate and the carb. The ported vacuum is normally he second port from the front on the base plate. What you describe is very strange.

 

The stock system does not connect the vacuum advance to ported vacuum!

The vacuum advance goes to one of the solenoids on the rack (I think the frontmost one?) which is connected to MANIFOLD vacuum, and the emissions computer turns it on and off based on the TPS and other factors. So it is in effect ported, but the computer decides when, not just throttle plates uncovering a port.

Yes, it's weird, but it is a byproduct of making a carbureted car meet emissions standards and OE drivability requirements.

There IS ported vacuum available at the baseplate, I think it originally went to the evap/breather valve. This won't work if you have a gasket between the carb and the baseplate, as the ported vacuum source is through a passage between the two. The OE setup similarly won't work if you have a gasket between the baseplate and manifold.

All that said... the point of ported vacuum is that it doesn't see vacuum at closed throttle. It should have zero effect at idle, so your rough idling has zero to do with the vacuum advance. In addition, if you want a smooth idle you want LESS timing! I get my bridge ports to idle and drive acceptably well by idling at 5ATDC or so, I don't let it see any advance until it is under load.


That's a relieved Group A spec bridge port idling smoothly at 1000ish RPM...

 

I will post some photos shortly.

 

Thank you PeeJay for your comments.

In my search for a ported vacuum, I removed the set screw in the attached photo. Once I realized this was not a plugged port but some type of adjustment screw, not sure what adjustment it is. Have not been able to find anything on the internet that mentions this. After reinstalling the screw and starting the engine, the enginer reved up to 4,000 rpm. As I backed out the screw the rpm came down, but running very rough. I've since adjusted it to where the engine seems to be happier, but idles around 1,500. So, long story short , after screwing around with adjusting this and the other adjustments on the driver side of the carb, I've managed to get the engine to idle reasonalbe smooth, but it now back fires under load when I take my foot off the throttle and cuts in and out after driving less than a mile..


Here are a couple of photos of the driver side of the carb




Looking for some guidance on how to adjust the carburetor. What I have found on the internet and my manuals, doesn't seem to match what I have.

Thanks