Hello. My 7 Backfires when I switch between gears, a few pops between shifting. Also, when I downshift on an offramp off the freeway, it likes to backfire a lot. I usually downshift to slow down, but would that be safe if its a rotary engine or if it backfires like that.

 

No, it's not safe if it's at the engine...use the search engine, we just had a thread on this...

 

Is it just a loud popping out the exhaust, or is it an actual backfire through the intake? If it's just an afterburn in the exhaust, it's more or less harmless. Just try to get the carb's tune dialed in and fix any exhaust leaks, and that should take care of most of it.

 

True story...I had my SA on the driveway and was letting it warm up. The local kids who were following the stereo build into the car wanted to sit in the seat and rev the engine. They already knew better than to touch the shifter, so I let one of them do it....at this time, it's stock with the thermal reactor and there was a crack letting in fresh air, so it was back-firing from there. The kids thought it was cool and it wasn't too loud, so I didn't say anything while I got some wire from the garage....next thing I know...POPaPOP...and then bellowing clouds of white smoke coming from the exhaust. The idle went to hell and I got in to pedal it to keep the revs up to move it into the garage but that was all she wrote. I let out the clutch, it died and never started again. I had it towed to Ari at Rotary Performance in Garland, TX who officially pronounced it dead......and that was just from the backfire.

 

That sucks to hear....i have an exhaust leak from the header gasket i believe...havent had time to get under it and pull the exhaust off to look. Im not driving it right now though...got a fuel leak....might get under it in the next few days and pull the exhaust to replace the header gasket.

 

when shifting and letting off of the throttle, there should be no backfiring on FB's. SA, yes due to the lack of a coasting and anti afterburn valve. what year is your 7?

 

If there is no catalytic converter installed, any RX-7 will back fire and belch some flames thru the exhaust, perfectly normal. But if it's coming thru the intake then yeah back thing

 

I have always thought that backfire in the intake would be the cause of the timing being off? Or at least thats what it was on my 91' celica lol....timing was off and that thing would backfire thru the intake sometimes

 

I have a full RB SP exhaust, and the only time my car ever backfires is if I take her right to redline and then let off. Big loud pop pop and a plume of smoke. But otherwise she behaves quite nicely. Also are you rev-matching on you downshifts or just throwing it into a lower gear and letting out the clutch? To save your clutch some life you should learn to heal-toe or just blip the throttle before you shift and then go to the brake.

 

^+1 on the anti-after burn valve.

Depending on the year, if your car has an anti-afterburn valve/air control valve assembly, that could be going bad. The AAV/ACV unit controls backfiring during deceleration and/or between shifts. Here is the link to the units, if you need a new one. But, I'd recommened checking the For Sale/Want to Buy section first if you might need one.

http://www.mazdatrix.com/b-egr.htm

 

my 13b backfires once in a while. only when i really get in to it. question what year is the car and engine what carb is on it. some don't have the anti after burner on the engines for some years. it could even be something like a small exhaust leak. my 12a used to do it all the time it really made me mad then when I switched to the 13b it doesn't do it hardly any more. it probably was the carb. it needed a rebuild so.

 

mines an 83. and its in the exhaust. and yes, I do have a catalytic converter on. state emission rules. i'm gonna rebuild the carb soon, and I probably think i'm running rich a bit, I havent touched any settings on the carb since I got it.

 

first start by adjusting the fuel but don't let it run lean a little rich is good. then if that doesn't work you will have to rebuild it. replace or fix all the things 85 FB has suggested. take it to a muffler shop and have all holes and rust in the exhaust system and maybe it should stop that anti-after burner is usually most of the problem on the carb'ed cars after they added those things. good luck trying to get it to stop though

 

Forgot to agree that an exhaust leak will also cause a backfire. I messed with an old SUV that had a hole in the muffler. During high deceleration, you'd hear a loud "POP" and when someone was following me from behind (in the dark) he radioed up and said that he saw a quick burst of flame.

Fixed the exhaust, problem solved.

 

Ok, so I should check these problems.

1. Carb running too rich, if not possible rebuild
2. Hole in the exhaust.
3. Anti-After burn valve.

 

Well, besides a hole in the exhaust, any opening along your exhaust piping, like the flanges and the sort, could also cause it, IIRC.

I can't remember if there's a way to check the AAV/ACV assembly or not. Give the FSM a looksee.

 

Keeping your foot on the gas a little as you shift down will probably eliminate the popping on decel, although this is not fixing the actual problem. I had the same problem in my '80. It has the whole decel system (coasting valve, dashpot etc.). The factory Service manual has the complete procedure for checking the system right from the aircontrol valve all the way through. Do this entire procedure (and learn while you go) and then if it's still happening, address exhaust leaks and carb settings. Exhaust leaks are a huge contributing factor to popping and loud backfiring as are carb settings (either too rich or too lean), but test the decel system first.

 

I gutted my Catalytic converter and disconnected my air pump. yes i do back fire

 

From what I heard, that's not the ONLY thing you do.

 

Meh, I need to go buy myself a tachometer, I knew I was gonna need one sooner or later. Too bad its too late to buy one right now or I would have already done so. Thanks for all your input guys! I'll get too it as soon as possible and let you know the outcome.

 

With everything stock, check for exhaust leaks first. The only fuel adjustment on the carb is the idle screw. This wil not cause the fuel build up needed to backfire. One of these days I'm going to find a way to make all of the carb guys read the entire carb manual and get some understanding about the stock Nikki, instead of guessing or parroting.

I don't backfire on the 12A 1/2 bp. That's due in part that my exhaust is tight and not leaking. The other reason is it's 3" all the way back. Pipe diameter doesn't allow for vapor concentration, I've tried, lol. Even when the exhaust is black from being too rich, no loud backfires.

If the exhaust is tight, then check the emission components.

 

Oh, so I'll check all of my exhaust first, make sure its all tight and no leaks.
Since I'm in Cali I have to have my emissions on, so I gotta check all the emission controls.
Good thing I bought myself a Chiltons Repair Manuel for my 7.
Thanks trochoid!