Another car, another problem

That doesn't necessarily mean a lot - check the battery voltage while cranking. If that falls below 10V on a 12V system you may have a problem.

What's the battery voltage with the ignition off?

Did you measure that or do you infer that from observations?

That is a possibility I haven't checked for yet, but I would have thought the electric fuel pump would tick rapidly if it was trying to move vapour rather than petrol. Also, the incoming pipe to the pump is a reasonable distance from the engine and manifolds - though I admit I haven't checked how close it gets to the exhaust along its run from the tank.

It is certainly worth checking for. And when I left the car last night, it was still refusing to start, so it will be interesting to see how much fuel is in the float chamber before the pump refills it.

Jim

I will check later today and report back.

Again, I haven't checked exactly this. But with the ignition on last night, I was getting 12.6V across the coil terminals.

The first time it failed to start (last week), I used the starter motor and 1st and reverse gears to park the car tidily. There was enough in the battery to move the whole car like that, which is a pretty clear indication that I haven't got a weak battery. Also, a weak battery will either spin the motor slowly or reduce the speed it turns it over after several tries. There is no sign of either.

Jim

Hmm. Check the voltage at the battery terminals - a fully charged 12V battery should have around 13V-13.2V if it's good. If you get around 13V at the battery but 12.6V at the coil, you may have a couple of corroded connections that increase the resistance in the circuits.

Trouble with added resistance is that is heats up the affected connectors, which may increase resistance over time. The symptoms you describe suggest that heat may well play a part in the non-starter scenario.

Yes and no. I was wondering if you had a dead cell - I've had that before, one cell was dead and the others were OK, so your basic checks suggest that you've got a working battery, but it won't play ball that well with the starter cranking, even though you don't get any of the obvious duff battery symptoms. But your 12.6V mentioned above pretty much rules this out.

Jim

What you describe is typical of the MG as well, I would have a look at voltage drop then. (Wiring on older cars can deteriorate especially BMC products.)

Pull the wires off the regulator and fuse box then put them back on, could be a dirty connection there. Not sure if they are screw connectors or spade, which ever, clean them up.

The generator goes to the regulator then the ign switch. In other words its not direct power to start the car.

Basically you have a wire that goes from the solenoid to the ign switch (white /red trace) then a white wire goes from the ign switch to the fuse, but not through the fuse itself, then on to the coil and distributor. Basically all the white wires joined together go through the ign switch, this is your power to feed the coil.

You can also bridge both the fuses and start the car from the solenoid without the key being turned on. This will give you ignition power. This will check for voltage drop through the ignition switch.

You can pull the hose off the float bowl and check the flow also the pump pressure is very low for the SU carby.

Secondly if you tap the side of the bowl and it starts the pump ticking rapidly its a sure sign its empty or if it overflows its a needle and seat problem.

Timo

Voltage drop, check by bridging the fuses and starting off the solenoid, bypasses the ignition switch circuit. Which is the most likely source of voltage drop.

This is the most common way and I would suggest this is the problem.

Gee its a Morris Minor there ain't much to go wrong. :)

Fair enough...

You're not wrong about that :)

I had this on my Capri with a Weber 32/36 DGAS carburettor. Turned out the carburettor was worn. There's a tube in the middle of each choke. Fuel passes from the float chamber into this tube and is then dispersed into the barrel. What had happened is this tube had become loose so the fuel was just dribbling down the side of the barrel instead of going into the tube. Upshot was that it'd start when cold when the choke came on but not when it was hot. Once it had started, it seemed to run OK.

Same symptoms as you seem to be experiencing. Yeah I know its a completely different carb but its worth a look.

As an aside, there's a dodgy batch of rotor arms doing the rounds. My dad went through three, even buying a new dizzy as he thought it was that, before he got one that worked OK. Basically what was happening was that the metal strip which acts as a kind of spring retainer wasn't doing the job so it wobbled about after a while. The first replacement came from near Northampton, the second from Driffield and the third was mail order from the owners club - all with the same fault.

Thanks. I am fed up with dodging the showers today, but I will try that. Also, I notice that the pump has a filter which could be blocked

- I will check and clean that too.

Jim

Bearing in mind that the battery is definitely not fully charged now - I spent nearly an hour last night turning the engine over checking sparks and voltages and I haven't put any charge back in it yet. A meter across the battery terminals showed 12.5V late this morning, ignition off. This dropped to 10.4V when the starter motor was turning (again with ignition off)

I have seen this with a dropper resistance on a Triumph. The Minor hasn't got a dropper though.

I will follow up Rob's suggestion of cleaning the connections to the fuse box. A couple of the spades looked as if they could do with a clean. Unfortunately then the showers started, so I have given up for today. It is pointless trying to sort out starting problems with wet electrics.

I will have to go for another run to get everything hot before I can experiment any further - it always starts first time when cold. So I will measure it again when it is charged up. But I have had a dead cell before (in another car, a long time ago), and it definitely affected the cranking speed.

Jim

Yes, worth a look. I did just once try pulling out the choke when it wouldn't start, and it made no difference, though.

I tried buying a rotor arm from Wares while I was buying the coil. Out of stock, waiting for more to come in. I can't see anything wrong with the one currently fitted though, and once the engine starts it runs OK.

I will have to hunt around in the back of the garage. Somewhere around I should have a scrap dizzy with the bearings gone from a Dolomite, but the rotor arm should be OK if it is still on it. Better a known old one than a doubtful new one, provided they are the same size. At least it will eliminate one option.

Jim

Jim

Small spark insufficient to fire the motor.

Then, whats the compression like? No compression when hot, also makes starting difficult.

Thats just to throw another spanner in the works :)

According to the documentation that came with the car, it had a full recon engine 2 years ago. Plenty of compression felt when turning the engine on the starting handle. I will, in desperation, check with a compression tester, but I really don't think it will show a problem.

A nice fat spark is seen at the end of the coil HT lead, though I admit that I haven't observed the spark at the end of a spark plug lead. Something else to check. Thanks for the hint.

Jim

Or run a wire direct from the battery to the coil? Then it also avoids any bad connections in the circuit.

Yes, that is one of my To Do list.

The trouble is that the car has now cooled down and the problem will have gone away, so further diagnostics will have to wait until I have time to take the car on another decent run.

Jim

I had a problem on my MG Magnette where I had a nice fat spark from the coil, but the rotor, distributer cap combination didn't work. There wasn't a good connection between the arm and the cap but if the engine was turned over holding the cap and rotor arm in contact (off the distributor) then it was fine.

I know you have checked them, but it might be worth trying new ones in case.

I still think that the stopping when hot sounds like a coil problem though - even though you have replaced it you.

dan

It is now a brand new coil. The old coil was hot to touch after a run, the new one was fairly warm. But the coil is mounted on top of the dynamo which places it in the airstream through the radiator, so it is bound to heat up a bit.

I couldn't get a new rotor arm from Wares - they are waiting for stock to come in. And I don't want to get one from Halfords because if anyone is going to have stocks of the bad batch it is likely to be them. I also need to have a really close look at the distributor cap under a magnifying glass to see if I can see any signs of tracking, but it looks fairly new and the carbon brush moves easily in its slot, so I don't really suspect it.

But the engine doesn't stop when hot, it just refuses to restart if I switch the engine off while it is hot.

Jim

Sorry if you've covered this, but can I check ... is that on the starter and with the handle?

Is the piston in the carb sliding smoothly? Is there oil in the dashpot? Is the float chamber breather clear?

Ian