I'm a rotary newbie, so I appreciate the help. I just bought a 79 in great shape except for a (hopefully) small problem. When I decelerate from abou 4000 RPM or more, I get a backfire. Occasionally, it will also stall at idle. The carb was rebuilt at the dealer in October of last year. New plugs and points were just installed a few days ago. Any suggestions on where to look next?

Thanks, I appreciate your help.

 

Some backfiring is normal esp. after high RPM.

Ensure that the dashpot is properly adjusted, that could be the cause of the stalling problem if I read you right. Ensure that the idle speed is about 750rpm.

 

I think backfire on deceleration happens with a lot of RX-7s, but especially with the early models. It's caused by residual unburnt fuel, which is inherent with the design of the RX-7 engine. Even with '84 and '85 RX-7s backfiring can happen, but it's pretty rare if all the stock equipment is working well. The only suggestions I have: when you're driving around town, try to remember to push in the clutch pedal before decelerating.. also, try to figure out which rpm gives the loudest backfire?

 

I'm guessing that you have an exhaust leak. That's what caused my "80 to backfire. If you have the stock exhaust, with the thermal reactor, the headpipe may have a hole in it underneath the heat shielding.
Those pipes cost over $1100, so if it has a hole you may need to have it welded. I did that before I got my Racing Beat header.

 

You might also want to check the butterfly valve in the intake manifold. Sometimes it gets stuck and causes the engine to backfire. You may also have a vacuum leak in the hose that runs into this mechanism.

 

'79 doesn't have the shutter valve. Neither does '80. That's why the '79-80 manifold is sooo much better than the '81-85 part.