BrianHeston

My car kind of sounds like it has jakebrakes. When I'm coasting down a hill, with my foot completely off the gas, doing somewhere between roughly 35-40 in 3rd or 4th gear, I get this repeated popping from the exhaust. It pops about every .5 - .75 seconds. It's not terribly loud or violent sounding. I have stock exhaust except for a straight pipe replacement for the cats. I never noticed this until doing this swap. If I give it just a tiny bit of gas, it quits. Is this a problem, or is it normal?

cpt_gloval

iTrader: (1)

that's what my 83 GSL did when i replaced the cats with a test pipe. my suspicion is this is pretty normal. does your honker valve work?

BrianHeston

I assume you mean my shutter valve. As far as I know it does, but I can't say for sure.

enigma32

Mine does the same thing...
It stopped for a while at one point, then started again.... Never figured out why

cdrad51

Mine doesn't do it, and I got a cat replacement pipe. Then again, it's a freshly rebuilt engine. I've heard that stuff is pretty normal though. I guess normally the cat would absorb and handle the extra unburned fuel, thus by removing it you get the soft backfires.

BigJim

It happens because a rotary doesnt burn fuel efficiently. In your exhaust there is actually unused fuel. When the unused fuel comes down the exhaust there should be no air thus no ignition. If your exhaust has a leak or is getting air it will ignite and give a "backfireing" noise. Only thing it harms is ur cats i believe,not real sure thou.

mckinneyml

Does yours also get kind of jerky to while going down hill?

My 1980 does unless I keep a little bit on the accelerator.

cdrad51

that's a carb issue. Yeah mine does that too, even on flat terrain.

BrianHeston

It does get a little jerky from time to time, usually a downshift and/or a little gas will take care of that though.

I was wondering if it may be timing related as well. I don't think I have any kind of exhaust leak for air to be causing the ignition for backfiring.

cpt_gloval

iTrader: (1)

oxygen could also be getting through the engine. again, not the most fuel efficient engine

cdrad51

It could be timing too. Easiest way to verify is, check the timing!

BrianHeston

Thanks for the tip cdrad51. I hadn't thought of that...

No, I just haven't had a chance to get over to my buddies place where I can use his timing light. I don't have one of my own yet. I just figured I'd throw it out here to see if anyone thought it was a likely cause, that's all.

Anex 570

79-80 didnt have a shutter valve, so I keep a tiny bit on the gas. My car wants to back fire but doesnt, must be from the header with a free flowing exaust all the way. Its a good idea to replace anything worn in the gas route to help on the backfiring.

Anex 570

79-80 didnt have a shutter valve, so I keep a tiny bit on the gas. My car wants to back fire but doesnt, must be from the header with a free flowing exaust all the way. Its a good idea to replace anything worn in the gas route to help on the backfiring.

BigJim

The shuddering that happens when u let off the gas is fixed with a torque brace, ull also get it in 1st and reverse gear really badly. Its when the engine tweaks to far i believe

cdrad51

Hey anytime buddy

I read you though. Check this out, I just went thru this with the timing:

https://www.rx7club.com/showthread.p...hreadid=308118

BTW, you can get a basic timing light for $30-50.

d0 Luck

advance the timing! if that's too hard, lean out your nikki carb! that's what i did and it worked.. just make sure not to lean too much

cdrad51

what did you lean, the idle? otherwise you'd have to change jets to lean it out.