Emissions Problem

Have a ARP 3.5 Litre block with a webber carb on it and a high lift cam. Took it in for an MOT and it failed due to emissions. I asked them what they would do to cure the problem they said tune the carbs. As this has a webber on, which is not really tunable with out installing new chokes, does anyone have any suggestions as to how to lower the emissions ?

(Just so we are all clear its in a discovery, not just randomly asking mechanical questions :-)

Thanks,

Richy.

Reply to
Subscription
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Have a ARP 3.5 Litre block with a webber carb on it and a high lift cam. Took it in for an MOT and it failed due to emissions. I asked them what they would do to cure the problem they said tune the carbs. As this has a webber on, which is not really tunable with out installing new chokes, does anyone have any suggestions as to how to lower the emissions ?

(Just so we are all clear its in a discovery, not just randomly asking mechanical questions :-)

Thanks,

Richy.

Reply to
Subscription

On or around Fri, 15 Dec 2006 16:11:30 -0000, "Subscription" enlightened us thusly:

what country, what test?

if the UK, then is it subject to a CAT test? If so, you'll have problems. If not, it should be idle emissions only and that is adjustable on most carbs, you'll need to find the idle mixture adjustment on your particular carb; I've yet to see one without.

if it's failing on high HC it can be due to burning oil, if the CO is coming out good. You can also get high HC from the CO being too low or too high, which mostly equates to too lean and too rich respectively. The figures IIRC are CO under 3.5% and HC under 1200ppm IIRC for pre-1993 and post-1975 vehicles.

If it's a post-'93 motor then it's required to pass the cat emissions test unless you can prove that the engine comes from a pre-93 motor, in which case it gets tested according to the year of the engine. You'll find it next-to-impossible to pass a cat test with a simple carb, I reckon, that's why all the modern stuff has EFi and closed loop fuelling.

Reply to
Austin Shackles

Leave the chokes well alone and play with jets if you have to.

Reply to
EMB

On or around Sat, 16 Dec 2006 09:29:03 +1300, EMB enlightened us thusly:

unless the carb is horribly mismatched to the engine it shouldn't take much to get it past a UK MOT, provided it hasn't got to pass the cat-level test - I'm not sure you *can* get a carb engine through that - it'd need very accurate setting up at the least.

Reply to
Austin Shackles

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