I finally am able to drive my '84 beige SE at real speeds, and I find it is backfiring. It doesn't happen very often, but at high speed (say 60-80). It seems to happen when I back off the accelerator - that is, reduce my rate of acceleration, not my speed.



In 10-15 minutes it happened 3 times, all above 60mph, but it startled me. The car sat for a few weeks, and the last 6-7 it was started it only idled or was just driven around the block (I always let it reach operating temp though) - could that be the cuase?



To make matters more challenging, I have very little knowledge about the exhaust I have (I just bought the car). It has a RB header that has been shortened. It then connects to a SS pipe with a two foot section in the middle that is about 3" diameter (2" diameter connectors on both ends), smooth at both ends (very professional welding) looks like a 2" diameter snake swallowed a 3" diameter sub sandwich. That bolts to the piece that goes over the axle, and then you have a short muffler (also SS).



So, there are no cats. I am not sure I will be able to pass the Texas safety inspection (non-emissions check county), but I will try tomorrow. I have the complete OEM exhaust, but I don't want to use it unless necessary.



The seller, who knew even less, said he thought it was straight through. He said his buddy saw sparks coming out the back one time at night.



The engine is very strong and responsive, the clutch and tranny are great, and the exhaust is very throaty when accelerating. At idle the exhaust is only slightly noisier than stock. The owner prior to the one I bought it from was trying to put it in a race config, and stripped out **a lot** of things. The EFI is still stock.



Any help identifying the exhaust components or resolving the backfire would be appreciated.



Thanks,

BTC

Im not sure you should be blaming the exhaust for this, It sounds like an air/fuel mixture problem, but I wouldnt change any setting just yet. If it sat still and was barely driven as you say, the carb could have gotton gummed up a little causing the engine to run a little lean. Have the carb cleaned and add some MMO to the engine and try it again.

The more a rotary motor is Modified the more it needs to be driven at much more than idle or around the block.

This could also be a small timing issue so be sure and have that checked also.

This has stock fuel injection.



I drove it considerably more today, and it isn't backfiring any more. In any case, I failed the inspection:



Inspector: "Uh...I can't seem to find your catalytic coverter. https://www.nopistons.com/forums/pub...1047683561.gif "

Me: "That is because I left it home in my garage." https://www.nopistons.com/forums/pub...1047683785.gif



I'll re-hang the "factory" exhaust from the RB header back, and see if it passes.



Thanks,

BTC

Every 1st gen rx7 i've been in backfires when you boot it then let off the accelerator. Thats how you get the flames out the back. https://www.nopistons.com/forums/pub...1047683561.gif

Or rev it to 8k and let off right away.....FIRE! https://www.nopistons.com/forums/pub...#>/biggrin.png

my 83 just blows lot of blue smoke when i do that



mike

You are right...it happened again today.



I was really pushing it, and then I let off the accelerator to coast down the exit ramp, and BANG!!!!



So, my next question...am I doing any damage to it driving it like that? I know fuel burning in the exhaust is the cause, but why does it only happen when you suddenly let off the gas?



Thanks,

BTC

check your throttle switch for bad spots (use an old analog meter)I just swapped out my switch and it fixed my backfiring on decell when my foot was just touching the gas

[QUOTE]but why does it only happen when you suddenly let off the gas?



Because there is very little pressure at that point and the unburned fuel is igniting in your exhaust rather than being blown through. BTW, these cars are not supposed to backfire - it's not normal. Beefing up your ignition is a good way to reduce or eliminate BF's - better spark means less unburned fuel (MSD is a good bet). Also, a lean condition will cause BF'd - are you running any advance on your timing? Any vac leaks? Too much air means Lean. Finally, you could also have an exhaust leak - check your exhaust system. I have an SE - zero backfires - don't let anyone tell you it's normal

Uhh, I wouldn't be to concerned about the back firing, my fb does it all the time, considering I put my foot into it more than I proberbly should, redline, and let let off, BANG BANG BANG and it throws flames, it doesn't concern me and I actually think it is rather cool.. and my cars a 'primered sleeper'. https://www.nopistons.com/forums/pub...#>/BURNOUT.gif

https://www.nopistons.com/forums/pub...1047683517.gif