jzr

Hi all,
Still getting used to my new-to-me '79 SA. A particular quirk is its propensity to backfire when the throttle is quickly lifted (like in a fast shift), especially when not fully warmed up.
As much as nearby pedestrians hate it, I kinda like it, but was wondering if the repeated shotgun blasts are doing any damage to the intake and/or exhaust systems. A search on "backfire" and "damage" together turned up nothing.

Thanks for the peace of mind everyone!

4ohfour

Is it a large backfire or a popping?

Most vehicles pop when the throttle is closed after a large run, it's a result of the fuel igniting in the exhaust system, the reason you don't get it when the engine is at full throttle is because there is enough backpressure to blow the remaining fuel out with the exhaust

(that theory was completly un-proven and i thought it made sense as I typed it, if it's wrong, please post why an engine backfires ((aside from it running rich which is a given))

cheers'

MyRxBad

backfiring, poping on a rotary engine = not good! Get it fixed, or you may end up paying the price (new engine)

82streetracer

iTrader: (1)

What, I have never heard of backfiring causing problems other than ballooning cheap mufflers.

zyounker

If it is poping, that is normal for an SA.. do you still have the thermal reactor?

You also might want to check your AVC or remove it and block it off..


-Zach

Barwick

Are you kidding me? My race car does that going into turn 6 on Waterford Hills (and a few other turns) and they (the RX-7 junkies at the track) said that's normal. It's got no cat, a small exhaust leak right before the muffler, and a not-so-restrictive muffler.

In my opinion, don't worry about it. I don't know what causes it, but one cool thing about it, if you have someone watch it, you *might* see some flames shoot out of the exhaust, it's pretty cool.

hanman

Barwick, chances are the exhaust leak is causing the problem.

jzr, two things.....
1. It is not normal for a stock RX to backfire. Usual problems are bad ACV or exhaust leak. Could also be in a bad state of tune.
2. When your car is cold you should really take it easy on it until it warms up. Rotaries do not tolerate abuse until they are completely warmed up.
hanman

jzr

So the consensus seems to be there is no consensus!

The car is definitely running a little rich, lots of unburnt fuel puffs out when it's cold in the morning. Mileage has been around 14, though it is a 4 speed. The car is completely stock, with all the archaic emissions gear intact.

In looking through the records, it appears as though the previous owner took the car in to the dealer at least 15-20 times over the life of the car to try and get the backfiring fixed. It never was. I think they replaced the Air Control Valve once or twice, I'll have to re-check the records.

Thanks for the input guys. If you hear gunshots in San Diego don't worry, it's just me!

zyounker

THE CAR IS AN SA!!!! THE DID POP WHEN STOCK.. This is because they do not have cats..


If he has removed his thermal reactor, and replaced it with cats, it shouldn't really pop anymore.



-Zach

peejay

You're new to rotaries aren't you?

Exhaust popping and banging is entirely normal especially on thermal reactor equipped (everything before '81) cars.

Sheesh my '80 would pop every time I let off the throttle. EVERY time. Double-clutched shifts would sound especially cool because of it

peejay

Not really. After I de-smogged the '80 it stopped popping and banging. Quite a disappointment actually. It has more to do with the tuning of the stock engine and exhaust leaks.

Thermal reactor cars are tuned VERY rich to make sure the thermal reactor is kept fed with unburned HCs. If the car doesn't run rich enough, the thermal reactor stops working and emissions rise. Combine that with all the air being injected into the system (and maybe an exhaust leak or two) and you have lots of popping and banging in the exhaust. The way the emissions system WORKS is basically like an afterburner - everything not burned in the engine is burned in the thermal reactor. And it makes plenty of noise in the process

mar3

iTrader: (8)

If the engine is older or high mileage the backfiring will take out the big "O" ring that surrounds the chambers. That ring separates the coolant from the center intake,compression and exhaust chambers. Ask me how I know this...

ps. don't let the neighborhood kids rev yer engine to hear the cool backfire no matter how cute it seems...

Aaron Cake

iTrader: (1)

Backfiring is completely normal.

yayarx7

I did this to a motor once. It required a big backfire though

peejay

I don't think that's what caused it. Backfiring (technically afterfiring) happens in the EXHAUST not the engine.

If the engine built up enough internal pressure to force the coolant O-rings to fail, the apex seals would die first.

Keaponlaffen

My '79 GS NEVER backfires. I'm running a stock '83 manifold on it, straight pipe, presilencer, and cheapo-canadian tire muffler. It used to backfire, but then I fixed the mixture and exhaust leaks. Now the only time it backfires is when I turn the key off, then turn it back on (really good for scaring the sh*t outta other drivers/pedestrians)

Jeff

MyRxBad

New to Rotaries... I don't think so... I've had 5 1st gen Rx-7's and owned rotary powered vehicles for about 13 years... New, I think not..

First of all.. He didn't say weather it was a RACE car or stock... I assumed stock, as most of us don't have race setup's. POPPING might be fine, depending on where it is in the exhaust. Backfiring will take out seals in a higher mileage engine. Meaning rebuild. So the best advice is to not have it backfiring or popping as rotaries aren't the cheapest to rebuild.

Popping in the 79-80 might have been normal because of the points setup not fully igniting the mixture. But most have switch out the points setup for a reason.

In the end it's personal choice. But my advice still stands.

peejay

'80 does not have points, it has electronic ignition. Besides, mine still popped and banged after I installed the MSD. The popping lessened when I fixed some cracks in the exhaust. Therefore the popping and banging is a result of oxygen igniting the HCs in the exhaust system. (Thermal reactor cars are tuned to run very rich to keep the thermal reactor fed!)

Please explain how afterfiri8ng can take out seals. It doesn't happen in the engine.

yayarx7

After firing may not take out seals, but backfiring can and will. I have had this happen to myself and Mar3 says he experienced it. A backfire destroyed the water jacket seal in my 12a (due completely to an idiot mucking about with a badly homemade ACV blockoff plate). I do not know the specifics of Mar3's mishap, although he said something about nieghborhood kids and reving the motor specificly to hear it backfire.

peejay

Well backfiring (traditional backfiring - through the intake) is a different matter entirely. I don't think we are talking about that though.

yayarx7

I just wanted to make sure that we all knew the difference between a backfire throught the carb and an afterfire out the exhaust.

MIKE-P-28

iTrader: (1)

Anyone have the old Uncle Buck BOOOOOOOMMMM lol

You rev the car up before shutting it off, turn the key off, get out of the car, and lock the doors start walking away, and it would GO BOOOOOOOOMMMM Used to love that !

abeomid

I've read on the other parts of the forum that a faulty ACV also causes backfiring. BUt do SA's have ACV??

I removed my emission stuff and ACV and now at every high RPM shift, my car shoots out a small flame and a huge backfire, pretty sweet

I'm gonna get some videos and put them up

jeremy

iTrader: (1)

mine did the uncle buck when i first got it running again but now it only does it very seldomly. i get a big boom when i shift hard from 1 to 2 or if i get on it really hard and let up fast. i have a 79 sa. i've had 2 or 3 that would have classified as small artillery. i also have multiple leaks in the exhaust and the carb still needs tuning.

hanman

I have owned a 1980 since it was on the floor at the dealers. It never started backfiring until things started to wear. i.e. it started to get out of tune, the exhaust developed leaks etc.
I currently have the same car with stock porting, RB header and presilencer, and the Yaw carb setup. It is running slightly too rich. But NO backfiring ever.
You can expect some small popping when cold with the choke on, otherwise it should not backfire.
As as far as rotaries go, I currently own four of them, and none of them backfire.
hanman