I've had a few FB's over the years but luckily I've had very little trouble with any of them.

I currently have a red '85 GS that's all stock and has a rough idle, especially off-choke. The car runs fine otherwise and has less than 20,000 miles on a new crate motor. It just idles roughly. And maybe a little too low.

I know very little about carbs, all my rx-7's have been EFI...

So where do I start first here?

 

first culprit to check would be vacuum leaks. a big leak that causes a rough idle and stalling is the anti afterburn hose. the hose will tend to crack from the heat of the exhaust and will leak, causing a rough idle. the hose is located on the rear of the acv and connects to a small tube on the intake manifold.

next, how good are the plugs? have you replaced the fuel filter or have you been into the carb at all? often times sediment collects at the bottom of the fuel bowls and will completely or partially clog the jets.

 

I haven't been into the carb at all.

The plugs are new.

 

is the afterburn hose on the exhaust side or on the spark plug side?

I should also note that it will stumble if I try and take off from a stop at lowish RPM's.

 

anti afterburn hose is on the intake/exhaust side, it's hard to see where it goes into the intake, it's on the bottom on the back of the intake by the firewall.

 

With pictures. https://www.rx7club.com/1st-generation-specific-1979-1985-18/hose-question-750125/

 

The anti-afterburn hose seems to be fine. I didn't take it off but it looks reasonably new and has no cracks or anything in it.

I messed with the idle screw and it's idling better but still stumbles on takeoff at low RPM - or when putzing in traffic at say, 1000-1500RPM.

Any ideas?

 

Run some Seafoam through the tank and see if that helps.

 

If it stumbles off idle my guess would be the accelerator pump... Too bad I'm not planning any trips near Windsor in the near future or I'd come give you a hand with that. Basically though it's probably a good idea to rebuild the carb.

Jon