GrandmoffSilvey

I just acquired a 1984 RX-7 GS. It sat in a shop for 4-6 year not doing a thing. It has 99k miles on the 12a engine and very little rust on the body. I have replaced the clutch master & slave cylinders and the break master cylinder. All oils have been changed. Many of the electrical connections have been cleaned off like head lights and such. And, all these components are now working just fine

I'm about the tackle the ignition system because there is intermittent backfiring. It occurs most often with mild revving and release of the gas pedal. There is also some at start up. I have tried several grades of gasoline and have noticed less back firing with higher octane. Other than this, the engine has a relatively smooth idle.

I was considering the removal of spark plugs and inspect them as well as distributor. But I figured I should ask the forums before going on a wild goose chase. Does it need the rotary equivalent of a tune-up, spark-plug replacement, distributor, ignition coils, etc.

Where should I start?

Mitchocalypse

iTrader: (2)

is the exhaust stock? ie. have you removed any of the cats?

I'm still new to the rotary thing but IIRC, if you have the cats removed, unburned fuel (which would normally be catalyzed and combusted in the cats) could essaentially combust simply due to the heat in the exhaust causing little "popping" sounds.

I could be wrong but..

959595rotor

Try checking the spark plugs to see if they are clean and correctly placed on the cap and plugs. they should be as follows lead or lower plugs 1 on front of eng 2 on back of eng ,trailing on top 1 on front 2 on rear,you might also have a leak or loose hose on your distributer, also clean the bottom of dist cap,or replace it if its corroded badly,I have also found that your small jets in the carb might need cleaning after sitting so long,you might also find, that the engine may need to be driven to allow the compression to build up, it just might be running too rich and washing the excess fuel into the exaust , like Mitchocalypse said, where it will ignite if the exaust is hot,

canonize-ryda

my 86 popps when shifting and when revving over 4-5k and when letting off the gas, but then again i have no cats and and fc na run rich so it to be expected

GrandmoffSilvey

Answers:

The muffler is the only thing that isn't stock and it appears to be a cheap one.

I ran seafoam when I was trying to clean out the intakes and engine w/o dismantling it. After about 700ish miles and oil change, I began high rpm driving to clear out carbon. The result of this has been an improved idle and engine response. But more prevalent backfires.

Update:
Ok something unexpected. I decided to let the car sit outside overnight and cool down. Next morning I started it to look for visible exhaust leaks. It turns out the previous owner used an old muffler repair kit (sheetmetal and what look like really long hose clamps) on the pre-silencer. There are leaks all around that thing. It seems that the pops are coming in the area of the pre-silencer.

Tomorrow:

I'll begin a process of replacing plugs and inspecting distributor.

Any further ideas?

P.S. I forgot to mention that it didn't leak before. The only question is, "Is the failure of the silencer patch due to the backfires or vice-versa?"

Kentetsu

I think you've identified your issue.

Holes in the exhaust system is the number one cause of backfiring. Every rotary will send some unburnt fuel into the exhaust system, and if there is any source for fresh air to get in then it will cause an "ignition event" inside the exhaust system. The stock air pump actually encourages that in order to keep emissions down, but that event would take place in a location designed for it.

Fix your holes and you should be just fine.




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GrandmoffSilvey

well the plugs helped have helped, but you are probably right about the exhaust. I just need needed an excuse to upgrade it anyway :-)