Carb and CAT surprise

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Tinkley
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Carb and CAT surprise

Post by Tinkley »

Recently discovered that the 1991 1.6 auto (XU52C engine) seems to have a CAT on the exhaust front down pipe!
Interesting combination with the Solex Z1 32-34 carburettor.... no wonder the emissions are way way off. It has passed MOT with this before but not this time!. Have sourced new front pipe so assume this will largely drop the CO level. Also about to do carb refurb especially auto choke L shaped piece where
the diaphram gets pretty hard due to modern fuel 'additives'. New down pipe is correct - no bulging CAT straight through type with twin wall near mouth to manifold joint.

Am I right in thinking this should resolve emissions problem? At least in primary sense, the rest of the tricks, clean oil, plugs, D cap etc easy to do.

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Jaba
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Re: Carb and CAT surprise

Post by Jaba »

Not sure how it would work on a carb engine but there is usually a lambda sensor too in the front pipe which adjusts the mixture via an ECU to minimise CO. On an injection engine you would have to refit the lambda in the new pipe without a CAT. But I don't think yours will have any of this so just adjust the mixture as lean as possible and hope the emissions run clean enough.
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Re: Carb and CAT surprise

Post by panky »

Not the same car but my 91 Mini Cooper originally had a cat/carb combination until I fitted a new exhaust, and as the cat wasn't compulsory for a car that age, I ditched it. I found it easier to get the emissions right without the cat as the car failed the MOT a couple of times with it fitted. Be careful about leaning off the mixture too much as this can cause incomplete combustion and cause the CO readings to go high, I learned this when I took it for it's first test after a five year lay off (welding engine/re-build/ re-spray) but the MOT man let me tweak the carb while it was on the machine and I watched the readings drop off as I richened the mixture. Been absolutely fine since with no further adjustment.
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Tinkley
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Re: Carb and CAT surprise

Post by Tinkley »

Thanks Jaba and panky. I'm almost certain some prat fitted a 1.6i front pipe, not even going to bother looking for the lamda sensor take off.
Local mechanic siad he once encountered a Mini built late '92 with this combination - it passed the great Austin Rover QA in the factory...
Mind you I have seen a Citroen ZX with 3 wheels the same diameter but the fourth... and that was straight off the transporter.

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Re: Carb and CAT surprise

Post by Kitch »

If the cat isn't ruined from running on a carb engine, it's probably quite a rare component. But yes, it wouldn't have had it from new. There have been the odd car with a carb AND a cat over the years (Daihatsu Charade IIRC), but not BXs.
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Re: Carb and CAT surprise

Post by xantia_v6 »

Cars with carbs and cats (not specifically BX) usually had air pumps to pump excess oxygen into the exhaust before the cat and the cats had a different chemistry to cope with that.

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Jaba
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Re: Carb and CAT surprise

Post by Jaba »

That cat will have some valuable rare metals inside. There is an epidemic of CAT thefts off cars while they are parked going on since lockdown ended. It is probably worth a lot more than the cost of the downpipe you are replacing it with. Although I have no idea how you can realise that value.

My TZi had a CAT and also had a Lambda sensor in the exhaust just before the CAT. I was planning to take it out as it robbed the engine of power and economy. Unfortunately it was written off before I got round to doing the upgrade.
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Re: Carb and CAT surprise

Post by Tinkley »

Re CAT thefts. Local workshop which does rebuilds/new kit cars etc had a load of CATs' stolen just over a week ago. Definitely something going on.
If I recall correctly the main rare earth materials were platinum and rhodium at least in the early CATs' which was of great financial benefit to Johnson Mathey and other South African mining companies...
Personally I would have preferred the more lean burn technologies to avoid a CAT in the first place as did several of the car manufacturers. I'm still convinced that almost all the polluting nasties could have been eliminated. Hard to get Nox down completely though without killing performance.
The true change is the alternative clean fuel/electric route - yet to be fully clear. Maybe several options yet.

Perhaps of interest is the fact it is getting very hard to get Carb refurb kits with the relevant choke diaghrams in this case Solex Z1/2 type. Found some in France and Germany but only one kit in the UK so well done Southern Carbs, Crawley.

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Re: Carb and CAT surprise

Post by Tim Leech »

That's a new one on me, the TXi was brought out to replace the carb fed model with a single point injection system fitted. If it doesn't need one I would probably remove it.

I have a spare front pipe for a 1.9 petrol carb which I am sure is the same?
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