So I just got around to dropping my rebuilt 12a into my 79 rx7. I have had it running and it's running rough especially at idle. But my biggest problem is that I'll run the car for 10-15 minutes to make 100% sure that it is up to operating temp (have since installed a temp gauge so I am positive it was up to operating temp on my most recent attempt) and when I shut it off it sounds like a toilet flushing almost, just running fluid, I took off the intake cover and air filter and found that the carb had filled itself up with fuel almost all the way to the top. I felt the return fuel line and it feels like it's not even pressurized, the feed line feels nice and stiff under pressure but the return feels soft and empty this leads me to believe that the car is literally depressurizing the fuel line by dumping all the fuel in the line into the carb. Me and my buddy both looked around and couldn't figure out what could cause this to happen. I know rotaries will flood if not warmed up but I've been able to replicate the situation multiple times now after turning off at full op temp. I don't want to run the car anymore until this gets sorted out as it's drinking fuel like crazy even when running and the dumping could wash the lubrication from the rotor housings and definitely don't want to damage my fresh rebuild. Any help any of you can give would be greatly appreciated!

 

Have you removed your gas cap to see if your tank has a bunch of pressure?

 

Just checked and there was no big whoosh or even any sound that would have indicated that pressure was released when I popped the fuel cap off.

 

You should do this right after a drive.

Another possible cause is the float bowl vent solenoid. If this is not functioning or stuck closed, the carb will easily overfill and flood the engine. Though it really only affects things while running and is not a cause of flooding after shut down because it is designed to spring closed when not connected to 12V.

 

Mine is having a similar issue to OP, not as extreme though. However, my vent solenoid is shimmed open. I'd be curious what the solution is to this.

 

Did you rebuild the carb? Did you use the new needles and seats? Since you just rebuilt the engine you must have had other things off and clean them up.

 

I actually didn't rebuild the carb solely because I'm still deciding between switching to a holley carb setup or something similar just so I have more modern stuff on there which is inherently simpler to deal with or rebuilding the carb, I'm just not in my comfort zone working with carbs as there are so many small pieces and it seems so easy to screw something up when working on one.

 

Holley would a huge mistake. Go with a weber or weber clone like the RacingBeat IDA kit or a Mikuni setup or Dellorto setup. The Holley is almost untunable for the rotary.

 

Idk, my problem with the weber stuff is that Racing Beat says on their product page that it's not recommended for a 12a stock port engine and also claim that the holley kit they make is pre-modified for whatever porting level you have like they have different carb kits for stock, street, bridge, etc. That's the only reason I had said holley to begin with.

 

Believe me when I say Holley is crap even from RB. Search on here and you will understand.

 

The rough idle points to a stuck float or something overfilling the bowls even while idling - not just when you shut it off. Check the fuel level at the sight glasses, should be right in the middle. My car had a dead vent solenoid (+1 Jeff20B) that caused similar issues. You should hear an audible clunk from it when you turn the key to run. Something else to check is the return line check valve. If it was reversed in the install it would cause a build-up of fuel in the carb (flooding). If it's none of that but assuming the fuel bowls are way high, I'd say pull off the air-horn and check the valves and seats, they're most likely stuck.

 

If you are planning on replacing the carb with a more modern, "simpler" carb, I assume that means there is no need for all the smog stuff on the stock Nikki. If that is the case, simply remove all that stuff and you will have a simple, very reliable carb. Much better than a Holley, Weber, etc. The Nikki carb itself works great, it is all the early 80's attempts at emissions control that are stuck on that make it intimidating to look at and work with. There is at least one good thread, explaining how to remove all that stuff.