MOT

[chrisfell]

It's that time of year again, when my car needs its annual MOT test. Although cars over 40 are no longer mandated to have tests, I still do mine. It means I get someone independent to check the work I've done over the winter. This year, along with taking 40 year old cars old out of the testing regime, our Government has determined that wire wheels no longer need to be tested. AT ALL. Loose spokes, rusted or broken, no longer a failure, not even an advisory.

And for the first time, just for information, I had the exhaust analyzed. Given the engine hasn't been touched for over 60,000 miles, I was interested to learn just how clean or not it was running. I wasn't expecting this:
CO 3.63%
CO2 11.40%
HC 150ppm
O2 1.59%
A/F Lambda 0.96

These are all incredibly good numbers. I've never managed to get a SU carbed engine below CO 4.5% before, and my old Dolomite Sprint was usually nearer 6%. Low HCs mean no oil is burning, so rings are still in very good condition. A/F ratio almost as close to 1 as it is possible to get a carbureted engine. Of course, these numbers are nothing like those of a modern high-compression fuel injected engine.

The MOT? Pass, no advisories.

[Turnip]

Congratulations on your clean sheet and clean carburation.
I too am of the opinion that it's a really good idea to have someone else check over your car at least once a year.

Simon

[christopher storey]

I hate to say this, but on the assumption that the CO was measured at idle , I would say your mixture is too weak by quite a margin. Your previous figure on a Dolly Sprint of 6% is much nearer what I would expect on a normally tuned XK engine, which equates to a stoichiometric ratio of perhaps 12.5 :1 which is spot on for an XK which require an atypically rich fuel mix at idle, query whether this is because about the only defect of the hemispeherical combustion chamber is that it does not promote swirl and/or squish in the way that other shapes do ( although conversely it is much more efficient at higher speeds and loadings )

[chrisfell]

I’m inclined to agree. The XK needs a rich mixture, normally. I’ll be checking plugs tomorrow, and then rechecking the mixture.

[Herzeg]

I had mine done two weeks ago and the guy told me that it most likely was a fail as the hazard warning lights were not working. Not having ever used them, this was news to me. He then went on the computer to check properly as he said they were not compulsory but if fitted they should work. I've always been of the same opinion and did some quick googling on my phone to check it.

Waiting for the inevitable fail paper, he then told me they did not need to work and he passed it.
I'm assuming it's just a fuse blown but will go and check it tomorrow.

John