For Richer Or for...Uhh, lean.
07-14-08, 09:13 PM
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For Richer Or for...Uhh, lean.
Well, first time poster, first time Rex owner...Heh, but enough rhyming, I've a problem with my FB!
I've just recently had an entirely new exhaust put on including: a new cat, cherry bomb glasspack, and a shiny new tip, all with 2 inch pipes.
Now, the muffler man,(Meineke's finest) tells me after installation that the exhaust is much too hot. Not cherry red. but still hot enough for the catalytic converter to be in danger.
So I take it to a very knowledgeable mechanic I know that specializes in RX7's, and he tells me that for some reason, I'm running WAY too lean, and that it's the reason my pipes are much too hot, and that a richer mixture is what I need to cool the pipes.
tl;dr How will I know when I've adjusted the mixture enough to fix this? Are there any tell-tale signs of a richer air-fuel mixture?
Also, will I need to adjust the idle as well? I've never adjusted a carb before, so any info is much appreciated.
I've just recently had an entirely new exhaust put on including: a new cat, cherry bomb glasspack, and a shiny new tip, all with 2 inch pipes.
Now, the muffler man,(Meineke's finest) tells me after installation that the exhaust is much too hot. Not cherry red. but still hot enough for the catalytic converter to be in danger.
So I take it to a very knowledgeable mechanic I know that specializes in RX7's, and he tells me that for some reason, I'm running WAY too lean, and that it's the reason my pipes are much too hot, and that a richer mixture is what I need to cool the pipes.
tl;dr How will I know when I've adjusted the mixture enough to fix this? Are there any tell-tale signs of a richer air-fuel mixture?
Also, will I need to adjust the idle as well? I've never adjusted a carb before, so any info is much appreciated.
07-14-08, 09:27 PM
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it will reek of gas when it's too rich, and maybe backfire when it's too lean. usually rx7's need extra thick metal because the exhaust is hotter than a piston engine.
07-14-08, 09:34 PM
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Sterling has a really good thread on tuning a stock nikki in the Arhives, take a liik for it
Edit: I forgot to add that the temperature of the engine itself is actually quite cool, it's just the exhaust that is overheating.
07-14-08, 10:06 PM
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The timing has been checked, and is right on. As for the cats, there is now one, rather than two since the new exhaust was installed, which I am told is fine, as the new one has the proper capacity to do the job of two.
I am still foggy as to when I'll know I've got the proper mixture. Am I looking more for a stable idle, or a certain sound to my exhaust?
I am still foggy as to when I'll know I've got the proper mixture. Am I looking more for a stable idle, or a certain sound to my exhaust?
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07-14-08, 10:07 PM
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Yes, check your timing. Also, make sure that the leading (lower) spark plugs are firing. Retarded timing will cause a hot exhaust.
Adjusting the mixture screw on the carb will only effect the idle mixture, not anything else. If you truly are running lean, then you'll have to rebuild the carb. You've probably got partially clogged jets. That's assuming that you are actually running lean (which I'm not convinced of).
On the other hand, RX7s (or any rotary for that matter) have extremely hot exhaust when compared to piston motors. That's why those cherry bombs will be toast in a few hundred miles (sorry). You need very heavy piping for this, and stainless steel packing, because fiberglass just won't take the heat.
Adjusting the mixture screw on the carb will only effect the idle mixture, not anything else. If you truly are running lean, then you'll have to rebuild the carb. You've probably got partially clogged jets. That's assuming that you are actually running lean (which I'm not convinced of).
On the other hand, RX7s (or any rotary for that matter) have extremely hot exhaust when compared to piston motors. That's why those cherry bombs will be toast in a few hundred miles (sorry). You need very heavy piping for this, and stainless steel packing, because fiberglass just won't take the heat.
07-14-08, 10:15 PM
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Yes, check your timing. Also, make sure that the leading (lower) spark plugs are firing. Retarded timing will cause a hot exhaust.
Adjusting the mixture screw on the carb will only effect the idle mixture, not anything else. If you truly are running lean, then you'll have to rebuild the carb. You've probably got partially clogged jets. That's assuming that you are actually running lean (which I'm not convinced of).
On the other hand, RX7s (or any rotary for that matter) have extremely hot exhaust when compared to piston motors. That's why those cherry bombs will be toast in a few hundred miles (sorry). You need very heavy piping for this, and stainless steel packing, because fiberglass just won't take the heat.
Adjusting the mixture screw on the carb will only effect the idle mixture, not anything else. If you truly are running lean, then you'll have to rebuild the carb. You've probably got partially clogged jets. That's assuming that you are actually running lean (which I'm not convinced of).
On the other hand, RX7s (or any rotary for that matter) have extremely hot exhaust when compared to piston motors. That's why those cherry bombs will be toast in a few hundred miles (sorry). You need very heavy piping for this, and stainless steel packing, because fiberglass just won't take the heat.
So, the actual problem lies in the plugs, or perhaps the entire carburetor. Depressing, but a good direction to start.
It really is too bad about the cherry bomb though, I suppose I shouldn't have listened to the service tech at the shop, he only told me AFTER the installation that he'd never even heard of a rotary engine in a car.
Well, I suppose I should have done more research too. Is there a specific brand of performance exhaust that works well with the high heat of rotary engines? Also, will my current cat burn up due to excessive heat?
07-14-08, 11:01 PM
#11
once again, there's plenty of threads concerning the exhaust preferences. and about the air/fuel mixture, i usually just go by smell or backfiring lol, i think blackdragonauto.com sells some sort of spark plug thing that tells you if it's too rich or too lean, and it'll let you know when it's just right, idk how well they work tho. and i'm sure there are other things you can use to properly test the a/f ratio.
07-15-08, 07:45 AM
#13
I think the only problem you have is the "normal" exhaust components Meineke sold you. I suggest you return the exhaust system to the shop. The tech already admitted he didn't know what he was doing. Rotary engines need extra heavy duty exhaust components. Cherry bombs may go first, but the cat and even the pipe will probably not last very long.
Here's some good info. Have the tech read either of the first two.
http://www.mazdatrix.com/e1.htm
http://racingbeat.com/FRmazda1.htm
http://www.rx7.com/store/rx7/saexhaust.html
Here's some good info. Have the tech read either of the first two.
http://www.mazdatrix.com/e1.htm
http://racingbeat.com/FRmazda1.htm
http://www.rx7.com/store/rx7/saexhaust.html
07-15-08, 11:00 AM
#14
Quoted from the www.rx7.com link, above:
I hate to have to correct whoever wrote this, but the stock 1980 exhaust does indeed use a thermal reactor and no cat... but it also most definitely has an air pump, which drives the thermal reactor outer shell, headpipe outer shell, and the heat exchanger.
1979-1980 Model
During the RX-7’s first two years, Mazda used thermal reactors instead of catalytic converters to meet the emissions standards. Because of the lack of an air pump and other assorted hardware required for using a catalytic converter, we do not offer a street-legal replacement for these year models.
During the RX-7’s first two years, Mazda used thermal reactors instead of catalytic converters to meet the emissions standards. Because of the lack of an air pump and other assorted hardware required for using a catalytic converter, we do not offer a street-legal replacement for these year models.
07-15-08, 01:00 PM
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you can always use your spark plugs as a way to tell you if you're close on your a/f. a lean mix will be white, a good burn will be a nice brown/tan color, a rich burn will build up carbon on the plug with some blackness...now this is a very simple breakdown, you can get pix of the plugs from different engine conditions to help you identify what's goin' on in your engine. it's generic, but it is simple and always available.
07-15-08, 04:34 PM
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Quoted from the www.rx7.com link, above:
I hate to have to correct whoever wrote this, but the stock 1980 exhaust does indeed use a thermal reactor and no cat... but it also most definitely has an air pump, which drives the thermal reactor outer shell, headpipe outer shell, and the heat exchanger.
I hate to have to correct whoever wrote this, but the stock 1980 exhaust does indeed use a thermal reactor and no cat... but it also most definitely has an air pump, which drives the thermal reactor outer shell, headpipe outer shell, and the heat exchanger.
07-15-08, 06:17 PM
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I think the only problem you have is the "normal" exhaust components Meineke sold you. I suggest you return the exhaust system to the shop. The tech already admitted he didn't know what he was doing. Rotary engines need extra heavy duty exhaust components. Cherry bombs may go first, but the cat and even the pipe will probably not last very long.
Here's some good info. Have the tech read either of the first two.
http://www.mazdatrix.com/e1.htm
http://racingbeat.com/FRmazda1.htm
http://www.rx7.com/store/rx7/saexhaust.html
Here's some good info. Have the tech read either of the first two.
http://www.mazdatrix.com/e1.htm
http://racingbeat.com/FRmazda1.htm
http://www.rx7.com/store/rx7/saexhaust.html
I stopped in earlier today on a lunch break to speak with him, and he kept trying to push the point that it was my engine running too lean that's heating the exhaust too hot, not his parts.
For the pipes to and from the cats, he literally told me he just had some "extra piping" that would "probably work just fine".
I really do regret ever going to this shop. I only hope I can rectify this situation without having to pay more than I already have.
07-15-08, 07:27 PM
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you can always use your spark plugs as a way to tell you if you're close on your a/f. a lean mix will be white, a good burn will be a nice brown/tan color, a rich burn will build up carbon on the plug with some blackness...now this is a very simple breakdown, you can get pix of the plugs from different engine conditions to help you identify what's goin' on in your engine. it's generic, but it is simple and always available.
was it running lean before?
what have you changed that would cause it to be lean all of a sudden?
07-15-08, 07:31 PM
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I just spoke with the Meineke man, and he's apologized for putting on the wrong cat, and muffler. He said it was a major mistake on his part. So he's saying he'll swap me out the correct parts for free labor. I just have to pay the difference in price for parts.
Does anyone know where I can order a very cheap stock cat/cats for my poor '83 fb?
As far as I know it was not running lean prior to my ownership, as I inspected the old spark plugs, and they were generally brownish/black in color. I have not adjusted anything but the idle in my month and a half ownership.
The car used to idle, about to die, at 500 before adjustment.
Does anyone know where I can order a very cheap stock cat/cats for my poor '83 fb?
Quote:
Originally Posted by boostedHULK View Post
you can always use your spark plugs as a way to tell you if you're close on your a/f. a lean mix will be white, a good burn will be a nice brown/tan color, a rich burn will build up carbon on the plug with some blackness...now this is a very simple breakdown, you can get pix of the plugs from different engine conditions to help you identify what's goin' on in your engine. it's generic, but it is simple and always available.
do this before going in and you will know if your lean or not and you can speak confidently, if this shop stands too loose money they will tell you anything, we have all been there at least once, if you have adjusted the idle mixture then you may need to shut the car off when not at an idle after some driving and check the plugs, this will give you an actual look at what the mix is like from the jets not the idle screw which may not be correct anymore, or correct the idle screw to mix right.
was it running lean before?
what have you changed that would cause it to be lean all of a sudden?
Originally Posted by boostedHULK View Post
you can always use your spark plugs as a way to tell you if you're close on your a/f. a lean mix will be white, a good burn will be a nice brown/tan color, a rich burn will build up carbon on the plug with some blackness...now this is a very simple breakdown, you can get pix of the plugs from different engine conditions to help you identify what's goin' on in your engine. it's generic, but it is simple and always available.
do this before going in and you will know if your lean or not and you can speak confidently, if this shop stands too loose money they will tell you anything, we have all been there at least once, if you have adjusted the idle mixture then you may need to shut the car off when not at an idle after some driving and check the plugs, this will give you an actual look at what the mix is like from the jets not the idle screw which may not be correct anymore, or correct the idle screw to mix right.
was it running lean before?
what have you changed that would cause it to be lean all of a sudden?
The car used to idle, about to die, at 500 before adjustment.
07-15-08, 08:02 PM
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Heres what www.rockauto.com offers http://www.rockauto.com/catalog/x,ca...,parttype,5808
Otherwise I've heard ridiculous things about stock replacement prices. If you don't have any emissions testing I would have the guy bend up a straight pipe to put in place of the cat.
Otherwise I've heard ridiculous things about stock replacement prices. If you don't have any emissions testing I would have the guy bend up a straight pipe to put in place of the cat.
07-15-08, 11:14 PM
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Heres what www.rockauto.com offers http://www.rockauto.com/catalog/x,ca...,parttype,5808
Otherwise I've heard ridiculous things about stock replacement prices. If you don't have any emissions testing I would have the guy bend up a straight pipe to put in place of the cat.
Otherwise I've heard ridiculous things about stock replacement prices. If you don't have any emissions testing I would have the guy bend up a straight pipe to put in place of the cat.
However, at present Colorado does not require emissions, but there is a possibility of it being brought back, so I just assume go with a cat.
07-16-08, 03:06 AM
#23
I've heard good things about Random Tech and Bonez cats. Most of the normal auto parts cats will not handle the rotary heat. Rotary Performance (the third link I posted above) carries Bonez. If you don't have testing, I wouldn't bother with a cat.
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