Engine: 2.3 Carb B23A/B230K: Mot pass......hurrah!!!

[BigGreenThing]

Well what a pleasant surprise!!!

Woke up early today, determined to start preparing for the MOT. Checked old certificate....MOT ran out last week. Sh1t.

Rushed around and booked it into local MOT station, having bought a back box for the exhaust (it was blowing slightly). The car sailed through it's MOT..with the only advisory being a slight blowing exhaust (which I had sorted moments after MOT was done).

Really surprised. Other than careful(ish) driving and general service and other bits and bobs...I have done little to this Volvo...spent months trying to resolve an engine-near-stalling issue when I apply brakes, and although it's not got worse - it certainly hasn't improved - the car still passes MOT.

Surprisingly, the CO2 testing came out at 0.51%!!! On a Solex Cisac Carb!!!

I guess it's running too lean? Or is <1% normal on Volvo 240's before Cat Converters came on the scene?

Anyhoo - I got a legal certificate of safety for the next 12 months.

Happy days!

[Michael J]

Less than three weeks ago my '89 2.3 with Solex CISAC was registered at CO 0.07% (max. allowed 3.5%), HC 26ppm (max. allowed 1200ppm). No cat, but it would have passed a cat test on those figures...

I had the plugs changed when some other work was done for this MoT (front brakes and the exhaust link pipe between the silencers, plus a little chassis welding) and they looked lovely. Not running lean. Last oil change was six months ago, new air filter then too.

[rusty244]

Originally Posted by BigGreenThing

Well what a pleasant surprise!!!

Woke up early today, determined to start preparing for the MOT. Checked old certificate....MOT ran out last week. Sh1t.

Rushed around and booked it into local MOT station, having bought a back box for the exhaust (it was blowing slightly). The car sailed through it's MOT..with the only advisory being a slight blowing exhaust (which I had sorted moments after MOT was done).

Really surprised. Other than careful(ish) driving and general service and other bits and bobs...I have done little to this Volvo...spent months trying to resolve an engine-near-stalling issue when I apply brakes, and although it's not got worse - it certainly hasn't improved - the car still passes MOT.

Surprisingly, the CO2 testing came out at 0.51%!!! On a Solex Cisac Carb!!!

I guess it's running too lean? Or is <1% normal on Volvo 240's before Cat Converters came on the scene?

Anyhoo - I got a legal certificate of safety for the next 12 months.

Happy days!

Congrats on the pass!!

Mine (B230A 1985) always comes out very very low on the CO - was 0.3% last time I think. Normally puts my modern daily driver to shame in this respect.

I do wonder though if this is in part due to CO being tested at idle for pre 1986 cars. Later cars seem to get revved up to around 3k rpm before being tested?

Regarding your stalling just find a good old school mechanic who is good at tuning carbs. May also need a replacement diaphragm and/or needle and jet. Local chap I found near me adjusts my Pierburg 175CDUS to absolute perfection every couple of years.

Prior to this nobody (supposed carb rebuild place and main dealer back in the day included) have had it running so well in terms of power and efficiency. Definitely worth getting it fully in tune for fuel savings alone.

[Michael J]

Originally Posted by rusty244

I do wonder though if this is in part due to CO being tested at idle for pre 1986 cars. Later cars seem to get revved up to around 3k rpm before being tested?

The revving to 2500rpm for a short time is to purge the exhaust system, the engine is allowed to idle for the test.

Ed: the CISAC is nothing like the earlier carbs, it's a twin-choke downdraught design. Basic maintenance consists of "leave it alone". :-)

[BigGreenThing]

Originally Posted by Michael J

The revving to 2500rpm for a short time is to purge the exhaust system, the engine is allowed to idle for the test.

Ed: the CISAC is nothing like the earlier carbs, it's a twin-choke downdraught design. Basic maintenance consists of "leave it alone". :-)

MJ...you're dead right. I think the first bit of advice I got on the CISAC from you (and Clifford Pope I think), was to leave it well alone and not "tinker". I heeded your advice and happy days. 0.07% CO2? Blimey. That's virtually alpine air coming out the end of the exhaust! That's incredibly good..and possibly indicative of the carb and EGR malarky working very effectively as they were designed to?

All I have done is replace gaskets I managed to find off another forum member.

Thanks Rusty! Waiting in the receptions of MOT stations always seems to have parallels with fatherhood and maternity wards! Nail biting stuff.

Seems like CO2 is healthy and normal then! As to the brake problem....I've banged on about it (ad nauseum) on previous posts. It's either a leaky servo or a big ol' vacuum leak I haven't located as yet.

[Michael J]

Originally Posted by BigGreenThing

... CO2? ...

No, CO - that's carbon MONoxide, i.e. not completely burnt, so very slightly fuel-rich*. Lots of CO means too much fuel, not enough air/oxygen to burn it all perfectly. CO2 (and H2O - water) is what you get from normal complete combustion, so there is no point measuring it.

Or you can cheat and catalytically convert your oily exhaust fumes to make it look at the tail pipe as if you have a good engine. :-D


Ed: * or possibly oil, both are shown by the unburnt HC figure.

[stephend]

I am surprised by the very low CO figures from a non-catalysed car. I would have thought that this is running lean. I've always believed that 1% is about right - and is what a 'modern' produces from the combustion chambers and going into the front of the catalyst.

Congrats to all on their passes, in any case.

[BigGreenThing]

I think you're right stephend. However I'm reluctant to tinker with the current carb I have on the car....which, coincidentally, need to get me safely from Hove to my old stomping ground of Cambridge!

[stephend]

You're right: if it ain't broke, don't fix it...

[honestjoe]

Well done to everyone who has a solex and lives in harmony with it..put a screwdriver near it and your asking for trouble!!..My solex has never been an mot issue ever..its usually wishbones..bushings..track rod ends oh and not forgetting weetabix trailing arms!!..all history now thank god..Cheers,hj.