irishminis.ie

Hi,

I've a 91 city that failed nct on emissiosn (amongst other things....).
The other bits I can sort easily enough but I don't know anything about carb tuning etc.

It passed on CO: 0.014% ( 3.50% threshold)
but failed on HC 1228ppm (vs 750ppm threshold)

Seems a little odd as if it was running rich it would fail on CO I assume so why am I getting a high hydrocrabon level?

It did seem to hesitate a little when idling just before test (but is running smoother now) so maybe it misfired a bit and a load of unburnt fuel triggered the high HC?

It hadn't been driven in a few years so it had probably done all of 50 miles. I've done a few more miles now and seems a little smoother.

My only other thought was maybe oil but it's never smokey, even on start up. She starts very easily too.

So, my questions is: should I adjust the carb to lean it out a little for test temporarily? Or maybe put some dipetane in the tank?

Any ideas? Thanks

Although not smokey the hydrocarbons would suggest burning oil.
Your CO is too low and a lean mix will cause ring ware, the correct mixture also lubricates the rings.
Since the car has been sitting the valve stem seals could be hardened allowing oil to pass through.
What I would do is set the CO about 2.5% and take the car for a long hard ( not cruse at 70 down the motorway) drive up the mountains with plenty of high revs to blow the cobwebs off the engine. Allow a couple of hundred miles before testing again.
Also check the crankcase for excess pressure and if there is high pressure remove the pipe into the carb and block the tube before testing

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TECHNICAL MODERATOR

Thanks woody.is 0.014% co definitely a sign shes running too lean? I thought maybe itbwas adjusted really well... I was thinking she was burning oil with due to low co with high hc. Hopefully it clears...

How would I check high crank case pressure? Try find the pcv and see if there's loads of air coming out of it?

I've already driven it a bit since it failed, a little enthusiastically at times... And it seems to be running much better (it used to kinda hesitate at idle with choke off). Fresh petrol through it might be helping too.

How would I go about setting it to 2.5% co? I was reading up and not sure how to do it. Some guides suggest cutting hole in exhaust and welding in a bung to allow a lambda sensor to screw in which would allow adjustment of the carb then.

Others say colourtune but supposedly its not great. What's the best thing to buy?

A quick pressure test would be to remove the oil filler cap and place your palm over the hole as you rev the engine. If you feel a lot of pressure on your hand it could mean that your breathers are blocked.
Old petrol won't help your emmisions as unleaded loses its octane after about a year. Any local garage should have a co2 meter to set the carb or go to Minifix in Santry.

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TECHNICAL MODERATOR

Sweet, thanks very much woody! Seems to be running totally different with fresh petrol. Might throw it into nct and see what happens. I'll look into getting co measured afterwards as don't want to do damage as you mentioned by running lean.