Fuel/Emissions

My Landy just went straight through its MOT
Thing is I'm sure it's running rich, it kicks out a puff of fuel smoke on start up, it smells rich when it's running. Whats confused me is MOT emissions test it gave 0.184% co2!

I think the carb may be worn so got a rebuild kit on order. Other thing it's started popping on idle a lot more than it used to and it bangs and pops on overrun which I assumed is unburnt fuel?

Hoping for thoughts and suggestions!

You want to be looking at hydrocarbons being emitted not co2 necessarily. Not sure what the pass requirements are for older vehicles but they are less stringent than modern cars.
Check you plugs and remember that 2.25 like to run rich and indeed should be run that way to a certain extent.

Check your timing, as popping on overrun is one of the signs of being slightly too far advanced.

What carb is it? The zeniths tend to warp and fuel can leak past the o ring that seals the two halves. Lots of threads on here for cures.

Hydrocarbons was 795ppm limit is 1200 so that seems about right.
Timing was done by ear it's running a Simon BBC leccy ignition on a Ducellier dizzy. Starts instantly and haven't touched the timing recently.
Carb is a weber
It does occasionally run on a little but very rarely and it does generally run well and mpg is ok.

I suspect you mean CO instead of CO2

The levels allowed are in the tables here https://www.gov.uk/government/uploa...t_data/file/194133/Emissions_17th_Edition.pdf

Smelling rich can be a number of things:
1) It's idling rich - for 1975-1985 you can idle quite rich up to 4.5% CO
2) It's idling lean - you can get a lean misfire which means every now and gain it will fart out a piston's worth of unburned fuel. If its doing this it should probably fail on HC emissions unless you're lucky
3) It's missing at idle (mine does this every couple of seconfs on electronic points but not on good blue lucas ones) again it will cough out a piston's worth of air/fuel mixture
4) It's leaking petrol from somewhere but its not coming out of the exhaust, carburettors do make a smell

Popping on the overrun is (kind of) a good sign really, it means your carb is doing its job and shutting off most of the fuel on the overrun. That requires the vacuum advance to kick in and pull the distributor to full advance, this is often not quite enough. Try ADVANCING your timing (not retarding as OSD says). You may find it starts to pink then though so a bit of faffing may be in order. If advancing won't clear up the popping check your points gap and try new spark plugs (I've just fitted a set of NGK BPR6ES for less than a quid each - get the resistor ones and you can hear the radio!).

The pop on overrun is caused by the mixture being very lean (the economy valve in the carb senses that there is a high vacuum and cuts almost all fuel off). Lean fuel takes more time to burn and is harder to ignite so is quite often still expanding when the exhaust valve opens, that leads to the rumbling the louder pops are that it didn't get lit by the spark at all or not properly and is ignited by the hot exhaust instead....I think it sounds good, certainly people know you're coming!

Whatever I do I can't get it to not pop on the overrun and never pink at the same ignition setting. I find I get best drive and mileage when there's just a bit of both.

Oops crossed over posting 750ppm is find but you will be able to smell it!

Apologies m'learned friend

Managed to get it the wrong way round!

That's what old age does!

Quarter past eleven!

dominicbeesley said:

Lots of interesting stuff

Click to expand...

Useful info thanks. So with the low CO reading it's probably lean at idle even though it smells rich. I will have a play with the timing and go from there.

Thinking back it does seem to pop more on idle since the leccy ignition was fitted but had defo got worse recently. Slightly off topic but when I removed the points for the new module, the dizzy cap sits slightly high, it doesn't quite sit flush on the dizzy. Only slightly the cap still clips on ok but it's a bit wobbly. Is this normal?

Carb is probably ok. I'd leave well alone.
If the dissy cap isn't on right you'll get all manner of bother. The magnet ring probably hasn't seated right on the distributor shaft. It can be a bugger to get it all on and seems to need more force than is necessary but I guess that's for a tight fit. Sort that out then reset the timing as it is probably out.

No worries Herb, I always used to get the two mixed up and you are excused as you are a diseasel fan.

dominicbeesley said:

Carb is probably ok. I'd leave well alone.
If the dissy cap isn't on right you'll get all manner of bother. The magnet ring probably hasn't seated right on the distributor shaft. It can be a bugger to get it all on and seems to need more force than is necessary but I guess that's for a tight fit. Sort that out then reset the timing as it is probably out.

No worries Herb, I always used to get the two mixed up and you are excused as you are a diseasel fan.

Click to expand...

Right had a look the dizzy cap is as well on as possible it is actually sitting flush on the dizzy but you can rock it side to side slightly, possibly a cheap cap?
Thought I'd check the plugs before looking at the timing:




They have been in for about 500 miles
Changed them and unsurprisingly it ran smoother/less pops!
Any thoughts?

Plug doesn't look too bad. Are you using octane boost or lead replacement stuff at all?

The cap should be on straight - make sure you've got it on the right way - there is a little metal tab that sticks out on some that has to engage in a slot. Most likely cause though is that your rotor arm is not all the way on - best way to check pull rotor arm off and see if cap fits better, in those electronic points kits you sometimes get two rotor arms - you may have fitted thr wrong one?

dominicbeesley said:

Plug doesn't look too bad. Are you using octane boost or lead replacement stuff at all?

The cap should be on straight - make sure you've got it on the right way - there is a little metal tab that sticks out on some that has to engage in a slot. Most likely cause though is that your rotor arm is not all the way on - best way to check pull rotor arm off and see if cap fits better, in those electronic points kits you sometimes get two rotor arms - you may have fitted thr wrong one?

Click to expand...

Yes I am using lead replacement stuff. Not every fill up but every few tanks I give it a dose. As for the dizzy, without the rotor arm the cap does fit slightly better, you can still rock it a bit but slightly more movement with the rotor arm on. Cap is defo on the right way and the rotor arm is tight against the metal shaft so no possibility of it going on further also only came with one rotor arm.

Tbh apart from the popping and fuel smell it runs sweet so if it's not running rich il take your advice and check the timing next

If it aint broke dont fix it. It sounds normal so just leave her alone!
They run a bit rich its not a problem

Don't bother with the lead stuff unless you put it in all the time, that just means you'll reduce valve wear by a third - its expensive stuff and replacement cylinder heads are quite cheap, I've heard from a few people that the valve recession thing is a bit of a red herring on land rovers but not sure how true that is...

If the cap fits different with the rotor arm on you've either not got it all the way on, got it on backwards or the magnet ring hasn't slid on properly - they are a right ***t to get on.

It's worth tuning them up if you want to save any money on petrol!

Thanks for the replies il check dizzy again and try to find an old school garage to set it up right. Easier said than done not many old school tuners about now!
Just want it running as well as possible got a couple of weekend trips coming up so want it reliable but sounds like it's not as bad as I originally thought.

It can't be that bad the plug looks fine which is a good sign...