solaxyfox

Well, I've certainly done it. I pulled my RX-7 into my smog class, and threw the 5-gas machine on her tailpipe, and started taking readings. Initially, There was near 0 CO and ~200HC with ~8-9% CO2 and O2... the Professor then told me that the O2 was throwing off the reading and I had to take off the smog pump and seal it, so I did.

Anyway, I ended up with 3-4k HC and medium-high CO... well, he started tuning it to bring the CO levels down ("Bring the CO down until the HCs start to go up" is his rule of thumb) but as he tuned it downwards, it started to backfire. Both he and my team-mate wanted to turn it back so it wouldn't backfire, but I shrugged them off, and now the engine is running a lot happier on the street, so here's my question:

Has anyone tried tuning a Nikki Carb using a 5-gas system? And without the smog pump attached (all other emissions stuff on) will the Rotary engine naturally want to backfire as it can no longer finish full combustion in the early stages of the exhaust system? I'm curious to this, because it sounds fine with the smog pump hooked up and the cleaner on, purred all the way home.

Also, if the smog equipment is removed, does the RX-7 gurgle-backfire under idle with a carbuerator? I have to admit that I'm just now taking the class seriously, and the intricacies of the Carb as still beyond me for now... I'll be doing a full rebuild in the week if I can get some extra cash, so that will probably help a bit, too.

altf4

you nailed it on the head. with the smog pump disconnected the cat isnt working efficiently so when that hot unburnt case goes out the exhaust you get self combustion whne it hits 02. but with the smog pump on the cat is in its efficiency rating and the car wont back fire cause that little extra fuel is getting burnt up in the cat.


did you take any readings after tuning with the smog pump hooked back up?

solaxyfox

Hrm, actually by the time the initial tuning was done, class was over and I had to hook everything up and shut it all down. The only readings I have are the initial readings with the smog pump @idle and @2500RPM. And one reading @idle without the smog pump.

Amusingly, the exhaust got so hot while running that the rubber hose over the other half of the tailpipe actually started to vaporize.

When I do a rebuild, I'll recheck the gas mixture to see if anything improved, and retune it then. I just wanted to make sure that it was going to backfire, due to the exhaust port not being able to recirculate unburnt fuel for scavenging (like the RX-8).

My Professor did declare my Cat DOA, though. The engine on there is a recycled engine, so it might also have a thermal reactor attached to it, if its not just a funky looking exhaust header... which would give me just about every smog control ever made on that car... no wonder it passed smog with better emissions then my 2000 Hyundai :P

altf4

cool. what year is it?



WHAO!! Youre from Sacramento!?! I just moved out of Sac are down to Az.

I lived in Roseville. I went to Sierra college and took auto courses there.

solaxyfox

Wow, small world I live in Carmichael and go to American River, though.

My car is an abused '83 GS (I think, based on options) that had red paint at some point, but its more of a muted color with rust bubbles here and there. I'm planning on taking a sander to it and getting some new primer on it when I can get it back into a garage (my apartment disproves of serious car work in the lot).

Small update for the tuning. The RX purred all the way home with the smog pump on, dispite having all sorts of backfires without it installed. It seemed a lot more responsive to throttle as well. Or maybe it was just happy I did something to fix some problems... o.O

Hopefully some time next week I'll get a carb rebuild kit and some new vaccuum lines and see what I can do to revive the car further mechanically. Then I have to rip apart the interior, check for rust, and reinstall the interior... and hunt down some faulty wiring (I think my door switch died recently).

Its *almost* to the point where I could probably go get another Rex in better condition instead, but this one is kind of like a loan, as I only have to pour money into it slowly

altf4

Go up to the Roseville/Antelope area and there are some auto salvage yards up there with ALOT of RX-7's most are FC's but ive seen a few FB's

Then there is also the Import only pick n pull on recyle road in Rancho Cordova...but ive only looked for VW and Datsun parts there.


you can usually buy a full parts car from them if you find a good one.