June 18, 2020 at 6:36 pm #2765
I’m looking for a bit of advice. I bought an A40 Somerset a few weeks ago and can’t get it to start. It needs a lot done but I thought I’d try and get the engine ticking over and then take it from there. When I received it, it had no battery so I wasn’t sure whether to connect the new battery as positive earth or negative. The previous owner said that it was negative earth but I know that they were originally positive. I’ve connected the battery to the negative earth and it turns the starter motor over but doesn’t start the engine. I’m wondering how I would know what way around the battery should be and will it cause an issue if I try it the other way round now.
I don’t think it is a fuel issue as I can see fuel in the carb. I put new spark plugs in and a new coil. I also wondered if it could be related to the dynamo. I tested the dynamo output with a multimetre when turning the engine over with the started motor and it gets up to just over 1 volt. Should the output be higher or is it just showing low because the engine isn’t running? I’m not really sure what to try next. The Dizzy cap looks ok and the rotor is turning.
Any ideas on what I should try next?
PaulJune 19, 2020 at 9:34 am #2769PeteJSKeymaster
Have you done all the usual basic ignition tests – e.g. take off a plug lead and (holding it with a thick cloth or insulating gloves!) hold it near the block whilst turning the engine to see if you are getting a spark?
As far as the car being negative earth is concerned, it may have been converted from positive to negative earth – though most aren’t. Given that you’ve connected it the negative way around, and assuming that the ammeter had been reversed to accommodate a previous change, then you should see the voltage drop when you turn the ignition on. If it has not been converted (and therefore the ammeter not reversed) you would see the voltage go up (from a mid-point of zero) when you tun the ignition on.
Does the car have a modern radio? This is sometimes a telltale that a car has been converted from +ve to -ve earth.
Other than that, if you’re sure that the carburettor bowl has petrol (and that it is fresh fuel – it does degrade over time), and that you have a decent spark, then the only other possible issue is ignition timing.June 19, 2020 at 1:22 pm #2773
Hi Pete. Thanks for the advice. I wasn’t getting a spark. I managed to trace it to the HT lead from the coil to the distributor. I’ve cleaned it up, cut the end off and reconnected it and it started. Happy days. The ammeter strangely is showing nothing and doesn’t change. Wonder what the problem is with that. I’ve got it wired with negative to earth. Does that mean that it has been converted as it starts? I haven’t got a radio in it.
Paul.June 19, 2020 at 10:45 pm #2775PeteJSKeymaster
Glad to hear you got it started, which I would say confirms it as having been converted to -ve earth. One of the advantages is that -ve earth cars rust less due to a property known as cathodic protection. A positively charged body, and salt on the roads in winter, are a pretty corrosive mixture!
As for the ammeter, its possible that it has simply been disconnected rather than reversed. It would be worth following the wires to it to see where they go if you can.June 20, 2020 at 3:45 pm #2777
Thanks for your help Pete. I’ll do that.
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