Bad, bad combination: Automatic and dieseling!

[Erling]

My 1987 240 GL has the B230K motor, originally equipped with a Solex Cisac carburettor. I have now found a nearly new Weber 36/36DCD as a replacement. Fitting the carb should be pretty straightforward, all I need is to do is to enlarge the mounting holes a little and it will fit on the existing intake.

The one thing that worries me, is possible problems with dieseling – the B230K has a rather high compression. To prevent this, the Solex carb has an electric circuit that shuts off fuel feed when the engine is stopped, a feature the Weber is lacking. And, as my car has automatic transmission, I will not be able to stall the engine - it will keep on running until the tank is empty!

What can I do if this problem occurs? I am contemplating replacing the mechanical fuel pump with an electrical unit, but the engine would still keep on running until the float chamber is empty, which again would make the next start harder, wouldn't it?

Your thoughts/suggestions are very welcome!

Erling, Norway.
http://home.no.net/ebrox

[cbyard]

The way to stop dieseling is to make the mixture so weak it won't burn. The obvious way to do this is to cut off the fuel, but you can also do it by letting in lots of air eg by opening a valve to atmosphere on the engine side of the carburetter.

I think the second method is more amenable to DIY ingenuity- maybe a normally open (close when the ignition is turned on) solenoid valve teed off the brake servo vacuum line?

Chris

http://pic7.picturetrail.com/VOL188/...8/23744414.jpg

Ref. the air valve Chris mentioned, Ford used just such a valve on quite a few of their (later) small OHV engines in Escorts etc.
It should be available from a Ford dealer or scrap yard.
Colin.

[Erling]

Thanks a bunch, both Chris and Colin. I think we're on to something! There are usually a number of early eighties, carburretted Sierras at my local yard - will they be candidates? Also, could I please ask you to be more specific? Are we talking about an electromagnetic valve (pulled from a Ford) spliced into the existing vacuum line between the intake and the brake servo? Or do I need to fit a new line (onto the vacuum line)? The valve should obviously be connected to a circuit that's turned on/off with the ignition.

A link to a picture or a simple sketch to help me understand the layout and what to look for at the yard would have been extremely handy...

Again thanks,
Erling
http://home.no.net/ebrox

[Erling]

To anybody who might also be taking the Weber route: There is a great page w/pics showing how these lines are run on a Weber-fitted MGB: http://www.mgbexperience.com/service/weber-hose.html

I also found that the full Haynes Scorpio-book was on the web, so now I've got a print-out of what this "anti-dieseling valve", "anti run-on valve" (those are good search terms) looks like.

Things are definitely looking up!

Erling.
http://home.no.net/ebrox

[Peter Milnes]

If you are in the VOC then peruse the Technical Driver back issues on this website. There is an article in issue 110 pages 39, 40, 41, 42, inside back cover and back cover, by our esteemed member Kay Campbell on Weber Carb Conversion and V8 power - 700 series. Kay is an extremely able lady with cars (ex R.E.M.E.) and has a better Weber conversion than the stock one. Do try to read the article, I think you will not need an anti-run-on valve. Incidentally most of us old'uns will recognise the symptoms you describe as being what happens when an engine gets coked up (over-rich running). There are a lot of cures for this with quite good results.

All the best, Peter

[Erling]

Sorry no, I am not a member – I’m in Norway. I tried to access the archives, but it has been password protected since my last visit. I guess I will try to offer to pay the club for a scan or a photocopy.

As for the valve, I actually found one this morning – from a 1985 Ford Courier. At least, I hope it’s the right valve, but with the parts number on it I hope to be able to check it with the local Ford dealer.

I was a bit muddy in my first post; I have not done the conversion yet. It’s still on the drawing board, the Weber and my car is at present 400 miles apart. The car is not dieseling at all with the Solex, my fears are that it may occur once I install a carb without any anti-dieseling device. Two reasons for my fears: Firstly, because of the B230K’s 10.5:1 compression. But also because of the previous owner’s, my father’s, very careful driving. I suspect that 15 years of rarely exceeding 3000 RPM may not have done the chambrs any good. Hopefully my bit of fun on the Autobahn this summer has cleaned things up a bit! Our equivalent of the AA actually advised me not to use any cleaning additives when I asked them. They said that in worst case soot could come loose in chunks around the valve seats. It made sense to me, so I refrained from this. I will be very interested in a second opinion: Any good brand names or experiences?

Also, do you think I will be happy with the Weber 36/36?

Thanks,
Erling.
http://home.no.net/ebrox/

[Peter Milnes]

Kay reccommends the 32DGAV carburettor from a Capri, Cortina Mks 3,4, or 5, 2 Litre Pinto engined Sierra, or Mk 2 Granada, complete with manifold, linkage and hoses, to make sure that you do not have to go haring down to the scrapyard again when halfway through the fitting. She gets 75 mph in 300 metres and a top whack in excess of 120 mph. As a bonus she gets 33 mpg at 70 mph.

Perhaps our Bob might be able to download a copy of the article as an attachment for you, but do ask him nicely as befits his good nature.

All the best, Peter