Rotary_Rocket_Guy

ok, I am new to this forum but I have had my Rex for about 5 months now and for a few weeks I have been having problems with backfiring. It only happens when i am decelarating, but if I put my foot on the gas pedal a very little bit it doesn't do it. I think it is running too rich, but what do I know? Can anyone help me out?

DONNA

Hi and welcome and i know you will get the help that youll need here, i had a backfiring problem as well as most all here have, you will probably learn to live with it, but i found that my shutter valve was bad which limits back firing, you can check yours by opening the air cleaner and checking if air is sucking thru the large vacume hole towards rear of housing and it has a large vacume hose (about 9/16 in. across), its not supposed to such air at idle, if it does u can just plug the hose up, i used a fishing cork, but u might can find a large enough bolt.....it still backfires but not as agressive as b4, some carb adj will help as well as other hints im sure youll be getting here,,,good luck.........

Pittdp

You could also get it fixed for about 150.00, Mine went out in 95 so I got it fixed and she has been running great ever since. I took it somewhere because it looks like pain to get to.

smnc

Welcome to the board and the world of the rex.

Backfiring is fairly common. As Donna said, get the carb tuned. Other than that, not to much I can think of.

What model car to you have?

SilverRocket

I don't think this has much to do with running rich. I had the same problem, when it got bad I could shoot flames out my exhaust by just reving in neutral. It was definitely my shutter valve ******* up. This was with no cats or air pump, and full Racing Beat exhaust.

I solved the problem by removing all the emmissions equipment on the car. I took off the rats nest, all vacuum lines except for the brake booster and oil filler neck lines. Plugged everything up on the carb. This way I guess the shutter valve is stuck open and doesn't screw up like it did before. As well, I removed the hot start assist and all the **** on the carb which controlled the air pump. As well I eliminated the ignition vacuum advance system.

The benefits of all this are absolutely no backfiring, smoother idle, overall better running, and less potential for problems down the road. As well, you will run a little richer now that all those solenoids which bypass air out are gone. I think rich is a good thing. The downside is your car smells absolutely revolting for people driving behind you!! And you'll never pass emmissions testing.

Anyways, sorry this is so long, but I did most of this at once so I'm not exactly sure which part of it cured the backfiring. If you actually wish to undertake this, any of the super knowledgeable people on the board can help you out!

Rotary_Rocket_Guy

It is an '84 GSL

peejay

You want it to STOP?

Hell I miss it... My used to pop pop pop all the time when letting out, and if I floored it and let off, you could count one... two... three... >>>BLAM<<< It ruled.

It would stop the pop pop pop after I'd weld the cracks in the exhaust system shut again, so maybe you have an exhaust leak.

Also, literally the night before I pulled all the emissions hardware (and stock exhaust and stock engine...) I found a vacuum hose hooked swayin' in the breeze. Never ever noticed it before, very weird. So I plugged it off, and whaddaya know, the engine hangs for a second after you let of the throttle... no more popping or blamming. But it made the car annoying to drive with the revs hanging like that (imagine trying to rev-match with a 80 pound flywheel) so I unhooked it again.

With no emissions, no nothin', it doesn't pop... but SOMETIMES it will let off a good BLAM, but very delayed. No consistency at all, so I can't let out a good BLAM every time I go under a bridge.

Rotary_Rocket_Guy

Ok so it doesn't really let out a huge BLAM as you put it, it just during decelaration without my foot on the gas pedal, and i know how when you start tweeking these cars they have a little Putt every once in a while(like every 3 seconds on mine) but this is faster and louder than normal and only during decelaration, OH, and I should mention that it has a brand new Exhaust on it, no pre-cats and a high flow cat, 2 and a half inch exhaust piping and a high velocity turbo muffler(very sweet) so it shouldn't have any exhaust leaks. I certainly hope this clears up a little confusion for some people.

Jeff20B

iTrader: (13)

Look at your exhaust stuff for any leaks.

Oh, by the way I completely eliminated all backfires with my little ignition mod, even with a few less than perfect welds in my exhaust system. But I can still get a good BLAM if I shut off the key in gear and turn it back on Hill are fun, but I need to try it in tunnels and under bridges

Pele

iTrader: (28)

What's your exhaust system like?

I'd assume you can do this in any carbed car with a straight exhaust.

RXcetera

This might come as a shock to some of you, but assuming everything carb related is working properly, a 1st gen RX7 SHOULD NOT BACKFIRE! The only 2 exceptions to this rule would be running your stock manifold with no cats and the 79-80 RX7 has a tendency to pop once its thermal reactor has reached operating temperature. Everyone else running a stock Nikki with a stock or headered exhaust that is backfiring are enjoying a malfunction in their carburetor.

Jeff20B

iTrader: (13)

Pele,
My exhaust consists of dual 2 inch pipes from the headers all the way back to the exhaust tips. There is an H pipe welded at around where the standard Racing Beat short primary header/collector would normaly have it's Y pipe (I've got a road race style header so it has no Y pipe).

It has two sets of three approved for rotary glasspacks (heh, a grand total of 6 glasspacks!). The whole system is 10+ years old and it isn't loud in normal running, but is very throaty and has good bass when idling.

It's easy to hear the engine sound change when the secondaries open, and going from single fire Leading to direct fire made the engine sound much different. I was also clearly able to hear the difference when going from the MSD to DLIDFIS. Yes, I CAN hear the longer duration sparks!

Back when I had stock ignition through the cap, it would pop every time I drove it. It would even pop after I shut it off. Then I went to PMDFIS and it still would pop sometimes. It also would pop right before it would fire up almost every time. The MSD prevented some of the pops but it did still pop after I was on the secondaries for a while. It also didn't sound as cool as it used to. Now with DLIDFIS I have absolutely ZERO backfires. It's amazing, especialy because I have not welded the exhaust, nor have I adjusted the carb. All I did was work on the ignition system.

I can hear every little miss while the engine is running. It only misses when the choke is on, and about 1% of the time while driving after the choke is off. Hmm, like maybe one miss in an hour of driving. Correct me if I'm wrong, but isn't that simply unheard of in the rotary world?

> I'd assume you can do this in any carbed car with a straight exhaust. <

Yeah, probably.

Rotary_Rocket_Guy

Ok, last time I failed to mention that me and my dad took the whole carburetor and cleaned it, but when we put it back on we came up with this extra part that didn't look like it went into anything, so I got my Haynes and my Factory manual out and I finally found out what that thing does. I believe it pushes on the thing that pours gas into the carburetor enough to keep a little gas pouring into it so it won't sputter during decelaration, because when I am decelarating I can keep my foot just kind of feather touching the gas, and it won't sputter, and if your wondering it is round and it has an arm to attach to the carburetor and it has a little white button looking thing that when you press it in, it comes back out very slowly. So I am going to try to put it back on this weekend, I'll try to keep you posted.

RXcetera

That's the Dash Pot. It keeps the butterflies from rapidly going back to the idle position when you let off the gas quickly. I've seen many dash pot assemblies that have loosened beyond effectiveness throught the years. This is one of the many causes of backfiring on Nikki carbed RX7s.

YellowJacket

>USING DEEP CAVEMAN VOICE<

POP POP BLAM GOOD!!! > <