340 1.4 rough ans slow idling

[Laird Scooby]

Originally Posted by Two340'sman

Just been typing this!

Well, my friend brought round two Gunsons gastesters, a Mk 1 and a Mk 2. The Mk 1 does differ, has different scale markings for one thing.

Mine is a Mk 2. My friends Mk 2 was in a box and all in pieces, in poor condition, bent meter needle, wire off the meter movement and as you said the setting pot, the slider was not making contact with the track.

I removed the pot from my unit, fitted it to his unit, carefully bent the needle as straight as I could get it, mechanically zeroed the movement and with some hot glue re-assembled stuff. The system is very badly mechanically designed!

Applied battery power and switched to check, needle moved full scale, so good so far. Switched to the other position and I could adjust the reading to 2%. Brilliant!

Warmed up car engine and tested CO, got a reading of 2.5%.

Adjusted down to 1.3 % and went to fill with petrol, did about 7 miles, car perfek.

Not sure what I’ll do with the other Mk 2 gastester to fix it. Now we have a working one, I'm a bit loathed to disturb it.

I think the problem with the rough slow tickover might have been grot in the carb, fiddling with the idle mixture screw may have dislodged it.

When an engine is running rich like it was, sooner or later the plugs can't cope with the unburned fuel so one or more starts to misfire which in turn makes the others run richer due to increased load. I'm not sure what the CO figure for yours should be but 1.3% sounds more in the right ballpark than 2.5 so i suspect you have finally got to the bottom of the problem.

There are a few subtle differences between the Mk1 and Mk2 Gastesters, mostly cosmetic really. I think the Mk1 was better built overall though. The Mk2 felt flimsy in comparison.

Originally Posted by Two340'sman

The Janspeed agent owner had lots of cars, I got to drive most of them. E-Type Jag, Jag XK 120, Aston Martin DB" perhaps, Jensen Interceptor, Bentley, Austin A40 with an MGB engine, Daimler Dart, MG Midget (of course with lots of Janspeed stuff), Mini Cooper S. and a Mini van with a 1275 engine. Probably other cars that I have forgotten, but his favourite was the Cooper S. The car went on display at main BMC agent Stewart and Arden in London.

Although a great enthusiast the Janspeed agent owner was a terrible mechanic, and terrible driver! Used to regularly crash his racing Mini, which was V fast, would out accelerate Jags in a straight line. I hope he does not read this post!

Originally Posted by Two340'sman

Janspeed was (perhaps still is) in Salisbury, I used to go down there sometimes, occasionally would meet Jan.

I think I was just slow to learn! the Tech College couldn't really have been better!

Last time i was at Janspeed was the mid 90s and then not really there, i passed them on my way to another business nearby. Seem to recall it was a small industrial estate on the outskirts of Salisbury.
I've met and/or heard of locally a few "racing drivers" who are terrible on the road - i used to live near a Toyota dealership owned by a guy whose son was in motor racing and had his own dealership (for Peugeot) in a nearby town.
I think his son contributed to more written off Peugeots than most of the rest of the population! Never quite got the hang of the fact it was firstly a road car and secondly it was on a road, not a race track!

[Two340'sman]

Amazingly, I found my copy of Practical Electronics Jan 1977.

Apologies for the bad scan, my scanner was made for XP, doesn't work properly in W10.

Co Meter by A60man, on Flickr

[Laird Scooby]

Eek!!! That's 'orrible!

While CO is a combustible gas, so are some others that come out of the tailpipe so immediately that calls into question how accurate it could be. Also it only gives a "Good-OK-Bad" indication so not really much use for setting the mixture, more a guide as to how economically you're driving. A better solution would be a simple vacuum guage i think!

However, it's fairly clever in how it achieves the output, repurposing a component designed to detect hazardous gases in other applications. It just doesn't lend itself to specifically reading the CO level like the Heathkit and Gunsons ones do, using the unique cooling effect of carbon monoxide on thermistors.

I nearly pulled the trigger on the "Buy it Now" on ebay on the one i linked to so i'm really glad you found and scanned the article - many thanks for that!

What i'm hoping to achieve is a circuit i can use with my multimeter (either my automotive AVO/Megger or my RS branded Fluke) to display the CO as a voltage. Will take some experimentation i think but will be an intersting project. Also if i can find a suitable sized moving coil meter, i might make an analogue version too.

[Two340'sman]

If you want the rest of the article scanned, please let me know. I can probably do better scans on my other PC with Linux Mint on it. The scanner works a bit better with this.

I have a few old moving coil meters around, bought new when Laskys (I think) in Soho closed down decades ago. I can look these out.

I've been interested in Hi Fi for decades, have a lot of Quad stuff, recently serviced four Quad 303 amplifiers.

[Two340'sman]

My Haynes workshop manual states that the CO for the 1.4 should be 1.5 to 3.0%. So my setting it at 1.3% is not far out.

I will check the reading again in a week or two.

[Laird Scooby]

Originally Posted by Two340'sman

If you want the rest of the article scanned, please let me know. I can probably do better scans on my other PC with Linux Mint on it. The scanner works a bit better with this.

I have a few old moving coil meters around, bought new when Laskys (I think) in Soho closed down decades ago. I can look these out.

I've been interested in Hi Fi for decades, have a lot of Quad stuff, recently serviced four Quad 303 amplifiers.

Originally Posted by Two340'sman

My Haynes workshop manual states that the CO for the 1.4 should be 1.5 to 3.0%. So my setting it at 1.3% is not far out.

I will check the reading again in a week or two.

Thanks, i'll see if i can find a bit more info on the Heathkit and/or Gunsons circuit and use that as my base for experimentation so i can use it to accurately set/read the CO using either a moving coil or external multimeter.

Interested in what you say about scanners working better on Linux. I'm running Bionic Beaver and haven't tried my newest all-in-one printer/scanner/copier with it. I bought it after the previous printer i had (that was allegedly win7 and 10 compatible) wouldn't work when my PC "upgraded" to Win10. All was good for a while until the November update of Win10 and suddenly the printer no longer works. It's been sat in a corner gathering dust ever since.
I might have to exhume it and try it on Linux, see if it actually works! Will be useful if so!

Thinking back to the days when my cars had carbs, i seem to recall many of them were specified as 2% +1%/-0.5% CO or as Haynes puts it for your car, 1.5-3.0%. Many other carb cars i had were 1.5% +1%/-0.5% and they tended to be the newer cars i had so i'd hazard a guess that if you've set yours at 1.3%, it's pretty close to optimal.

[Two340'sman]

In Linux Mint I use Sane and Xsane for scanning with my ancient Canon scanner.

https://www.linuxlinks.com/XSane/

I could not use W10 without OpenShell (start menu), Shutup10 and Windows10 debloater.

I use Windows 10 LTSC, in my view the best version of W10.

[Two340'sman]

10 Mile round trip in 340 today, perfect! Tonight, a trip to Aldi, fingers crosssed!

Your theory of rich running and the plugs sooting up one by one is very plausible and is likely what was happening.

Had a look for meters, only found this one, new old stock.

You are welcome to it if of any use.

Meter by A60man, on Flickr

[Laird Scooby]

Originally Posted by Two340'sman

10 Mile round trip in 340 today, perfect! Tonight, a trip to Aldi, fingers crosssed!

Your theory of rich running and the plugs sooting up one by one is very plausible and is likely what was happening.

Had a look for meters, only found this one, new old stock.

You are welcome to it if of any use.

Meter by A60man, on Flickr

Thanks very much for the amazing offer, let me have a dig through my stash over the next few days as if i already have one, perhaps someone else could make use of it but let me look first!

[Two340'sman]

Well, even the Aldi trip in the 340 was a success, car ran fine. Gave a lift to a neighbour who used to run a BMW model ?

He thought the 340 was running very smooth and quiet. One doesn't really get any gearbox noise, it being sort of behind the rear seat.