I don't know what's wrong with my car but I have more and more backfires... I'm sure it has something to do with the timing but I'm not quite sure to what I should put the leading/trailing on my '79 12A RX-7. I searched for a while on the forum but there is a lot of contradiction so I don't know what to do anymore. I think I even have a hole in my muffler because I think there is more sound. In a month I will buy a Full RB Exhaust system that will fix the problem.

I do have one question though with the RB System, when I put the new exhaust system, I don't need my airpump anymore, so that means I can remove it. When I do that, I need to put a double pulley too no? Since I won't have my thermal reactor anymore, the car won't need fresh with that old and rusted pipe?

 

I don't know if I'd go spending $500+ on a new exhaust system just to fix backfires... If I were you, here's what I'd do:
Convert to a 81+ distributor
Install DLIDFIS:
http://www.geocities.com/cd23c/dlidfis.html
Remove rats nest and air pump:
http://maz_tutorials.totalimmage.com/
Mechanical secondaries mod per instructions found here:
http://www.geocities.com/sevensportrx7/snikki2
(theres another with pics somewheres, but I can't find it)

The distributor conversion will take care of maybe 50-75% of the backfires, at least, that's said from my experience with this mod on SAs. This coupled with DLIDFIS will likely fix them all. However, the only problem that is likely happening here is your points are worn or drifted. If you want to be lazy and just replace the points, that'd be okay, but if I were you do what I listed above. The total cost of those mods should be under $50 and you would see a big difference. Oh, and you shouldn't have to get a dual pulley if you use the lawnmower belt as mentioned in one of those articles. Part number 3L220, I believe...
Anyway, good luck.

 

Check the carb fuel mixture as well for vacuum leaks

 

More than likely, all your backfires are caused by the carb. When the carbs get old, they dont mix right or correctly as quickly as they used to. When you let off on the gas, you get really bad mixtures and the backfire during shift.

I found most of my backfires went away after I tuned the carb. Make sure your carb is tuned to as close to stoich at idle as possible. If your car is over .4 mv or rich you'll get the backfires. You can try leaning here out a half turn and see how your back fires change.

Backfires are unburnt HC's that pop out the back. I would be inclined to think that removing the air pump would make your back fires worse. What happens is, the mixture doesnt get enough air in the pre mono converter to burn those HC's. I know when I fixed my ACV that the loudness of my backfires decreased.

 

I haven't read all the posts yet, but take out the airpump and block off the acv, as soon as i did that my car never backfired again

 

The '79 RX-7 does not have a catalytic converter, but rather a double-walled exhaust manifold called a thermal reactor. The '79 also does not have the shutter valve on the intake manifold that the later FB models do. As a result, the system is very prone to afterburn unless everything is tuned perfectly.

Check your idle mixture settings, as they make a huge difference. Make sure your points are in good shape and check the dwell. There are also a couple of solenoids that control the anti-afterburn system that can be checked very easily. If you have a factory or Haynes manual, they detail the procedure.

As for the timing, get a timing light and follow the instructions. Just make sure that the leading timing is on the yellow mark and the trailing is on the red. Do this check at idle and at 4000 rpm to check the total advance. Again, a manual will detail how to adjust the timing if it's off. (I'm giving you a hint here. If you don't have a manual, buy one, they're invaluable.)

Good luck with the '79.

 

It does however have what they refer to as a coasting valve
Same principle.

 

when I put my exhaust, my backfires went away,

they turned into faint pops when flames would shoot out the tip.

 

did you take off the air pump?

 

Hey my 80 backfired almost everytime i let off the gas or turned the car off. I replaced it with a full rb exhaust and i never have heard a pop since! I still have my air pump hooked up but i didnt block nothing off yet. Still gotta get to that. Rex79, go with the racing beat system it should take care of your probs. Plus give you a good bit more power. Its worth the money i think.

 

Backfiring..lol

Something I hope will never happen again.

I was runnign so rich ..I can turn the car off and start the count down by 5 secs later it used to sound like some 12 gauges going off. at one time...I hated to go some where packed,in public...I would have to get otu of the car and make a run for it,One time i was near a cop and thought he was goan drawn down on me..its so dam embarassing..

 

lol so what did you do to fix it? play around with the a/f mix? timing?

 

Rejet carb,played with mixture screws../timing

 

its most likely the air fuel mix, cause my GS back fired like a **** when I got it, after leaning it out a bit the backfiring went away. car still runs like **** but thats another story....

 

Since I don't know much about the Nikki carb... I should ask a mechanic to do that?

 

Ohh I dont have a Nikki ..I run a Holley..

I dont what jetting etc you can do to a Nikki,I think if your not running in a races restrictive class,dont waste yoru time with a stock carb,get it running to whwere you need to use it for normal driving and save for better...

 

lol my car is now doing the exact same thing. Even with the power pulse muffler, the bang 5 seconds after I shut the engine off is scary, will set alarms off and make people turn their heads. Carb seems to be on its way out, accel pump is leaking.

 

That has everything to do with your idle mixture as its to fast and or too rich when you shut off. I dont know if that fella that made this thread solved his problems, because none of the above make any sense to me being as I have first hand expeirence with back fire. Mine does NOT do it now by the way.

 

Yeah? well I leaned my idle mixture until the screw almost came off, and it didn't change shiate

 

Thats not leaning it... thats making it rich. Lean would be all the way in being its shutting off the fuel basically. Also you have to mess with the idle speed, when i rebuilt my carb it adjusted so it idled at 2000rpm, guess what happened when i shut it off, everytime.

 

Ok so now I'm confused. Somewhere else I read that turning the idle mixture screw counterclockwise will lean the idle, and screwing it in (clockwise) will make it richer. Which way is it then??

 

depends on your carb. Its easy to find out! Turn the screws all the way in, and if your car dies, you know your leaning it out