The Lotus Grand Tourers

You should be able to smell the incomplete combustion of 5.8% CO (12.3:1 AFR) at idle. These figures are more like what the main circuit should be producing under load (power).

The adjusted 3.4 % CO (13.2:1 AFR) at idle is still on the rich side. If all your engine management gizmos are working and your air filter is new (clean), fresh plugs and ign timing spot-on you'd get below 1% CO (14.1:1 AFR) at idle easily with no running problems and some fuel saving.

This figure shows relationship between AFR and CO etc ...



This table clarifies AFR and CO% readings ....


If you clean and gap your plugs plus renew your air filter before the next MOT you should have a chance of keeping the CO % below the pass figure.

The air filter is a life time K & N filter. I have a cleaning kit for it so will give it a clean. Plugs are probably due a change anyway. Thanks for the info - could do with a gas analyser at home!!

No numbers, again, this year. But is passed again. One advisory on PAS pump possible leak (probably a disturbed hose seal from when the rack was replaced in December).

Not sure how it passed because it's been fouling plugs on 3 cylinders for months and nothing I do to the carbs seems to improve it.
Cold start with choke is usually the worst for it, and results in running on just 2 or 3 at best, but there's a definite build-up over time even without the choke.

Mine passed at the end of January but I have been busy moving house and struggling with access to this Forum - hence the delay.

CO = 1.32
HC = 100

The carb jets were thoroughly cleaned and carbs re-adjusted during the year.

Mark.

Mines just passed . Nothing done to the carbs. Just plenty of use with a 125 mile run to the MOT station

HC - 53.

Mine has an MOT pass today
CO 1.89%
HC. 154 ppm
One advisory - near side rear wheel bearing has slight play

MOT passed yesterday with no advisories this time.

CO 0.35%
HC 115 ppm

I purposely set it lean @ 0.5% CO about 3 years ago (on Iridium plugs) - so 0.35% is in the ball park given differences in measurement accuracy.

All engine management gizmos working, Tesco 100 RON in the tank and it runs sweet atm. Purge pump working so started first time after filling-up.

Mot passed no advisories

CO 1.91%
HC 327 ppm

MOT passed with no advisories.

CO 1.611%
HC 556 ppm

Checked my emissions with my CO analyser which did read 2.15 so knew it would pass.

Ian.

First test after the engine rebuild was completed a couple of years ago - the last two MOT testers decided to be nice and "not bother" with the emissions test, which was actually quite frustrating as I wanted to know I did an OK job! Anyway, after about 10,000 miles on the rebuilt engine, my results are:

CO - 1.68%
HC - 758 ppm

I did increase the idle to around 1,200 rpm before the test - I'd be curious to see what it'd get at 800-900, where I normally set it.

My car passed it's mot yesterday after being off the road for 9 years. When I got it home I got it running on the fuel that was in it although I did put a few gallons of fresh Asda fuel in it before taking it to the garage and I didn't do anything to the carbs. Car is an Excel LC with 71000 on the clock. I was well chuffed when it passed.

CO: 2.036
HC: 909

A year later, with 12,000 miles and 3 years since the engine rebuild (didn't do many miles in the last year!), and the scores are:

• CO - 2.44%
• HC - 751ppm

Idle set to 1,200rpm again.

rbgosling wrote: ↑

Thu Apr 15, 2021 17:34

A year later, with 12,000 miles and 3 years since the engine rebuild (didn't do many miles in the last year!), and the scores are:

• CO - 2.44%
• HC - 751ppm

Idle set to 1,200rpm again.

CO increase ... if your air filter is new and your ignition timing is advanced correctly I'd check carb balance and if spot-on, slightly lean your idle mixture screws ...

Timing and idle mixture screws haven't been touched since last year, but then neither has the air filter so it's not the newest. Still, 2,000 miles of driving shouldn't have made the filter too badly clogged.

Without access to an exhaust gas analyser to see what happens, I'm reluctant to start playing around with the idle mixture screws, at least until the emissions become a problem, and there's still plenty of leeway at the moment.

rbgosling wrote: ↑

Fri Apr 16, 2021 09:10

Without access to an exhaust gas analyser

If any meets happen and we’re both there I have a handheld Snapon gas analyser I can bring.