Talk Morgan Forums Morgan Sports Cars Classic Morgans (pre-CX) Loss of power and cutting out when driving

I've a 1972 4/4 1600 and when driving for a while (say after 30 mins), the car starts to lose power and then cuts out. After 20-30mins, it will start again (with a struggle) and go for another 10-15 mins before the same happens again. I've replaced the coil a number of times, fitted an electronic fuel pump, new distributor, rotor arm and alternator, but this hasn't solved the problem. I left the car running at home for over an hour, but cannot simulate the issue, although I did not that the coil was hot. Has anyone experienced this problem and found a solution?

Could this be fuel vaporisation due to high temperature under the bonnet. You might be able to check this by reproducing the fault on the road, then immediately spraying carb starter fluid into the air filter and seeing if starts immediately (it should then falter and stop quickly as the carb starter will only last for a few seconds). Rerouting the fuel lines or putting some heat insulation on them may help.

If the vent hole in the filler cap is blocked, it might be that a partial vacuum is building up in the petrol tank limiting fuel flow (which gradually goes away after a rest).

I think the coil should get warm but should not be too hot to touch. Does your car have a ballast resistor in the low voltage feed to the coil? If this has gone short circuit, the you may be running a ballasted coil (which expects 7-9V) at the full 12V which will certainly make it hotter. You can test if you have a non ballasted coil by measuring the coil resistance. It should be about 3 ohm for a non ballasted 12V coil, or about 1.5 ohm if it is intended for use with a ballast resistor. (The use of a ballast resistor was normal in 72 I believe).

If you haven't changed the plugs and plug leads I'd do that too, as it won't cost much.

Why have you replaced the coil a few times ?

My first thought would be something electrical - condensor on conventional, or a cheap Accuspark/Powerspark unit.

Second would be fuel starvation - what's the inside of your tank like? Fairly easy to take a peak. On mine, it had been lined at some point and the e10 fuel had broken down the lining and it would block the fuel pick up in the tank. Once I'd stop, a little fuel would flow back down the pipe, clear the blockage and it would be OK for a while.

May suggest why you can't replicate on the problem while running on the drive - although you're getting the heat into the electrics, you're not getting the same demand for fuel as you would be running out on the road.

Agree with the other checks mentioned - fuel filler cap breather, and ballast resistor wiring (I removed mine and replaced coil with a non ballast type with direct 12V feed.)

Had this a few times over the years (each time with MGBs)

First time was a failing condenser second time was the little pig tail wire inside the dissy that had gone resistive.

On another occasion it was a sticking needle valve in the SU float chamber

I've got my money on the Condenser, problem is new ones are often cr4p quality

I had similar issues on mine a few years ago, i thought it was fuel, checked everything, no.

Working on ignition, I reverted back to points & condenser with a new ballast resistor,from the lumenition, changing HT leads, plugs & coil.
Most of these are cheap enough on a 70's 4/4!

After a process of elimination, I finally found the problem to be a hairline crack in the distributor cap, which caused the issue once the engine was hot.

Good old Lumenition back in play as that wasn;t the issue and far more reliable than points in my experience.

It may not be the same issue as yours, but just keep working through component replacement until you find the cure.

Good luck!

I had a similar problem with my +8 - it was traced to water ingress into the immobiliser receiver under the dash - the sparky bypassed it and no problem since.

I had something similar occur once with my 89 Plus 4. Running at 3500 to 4000 rpm it would suddenly cut out. Once the restarted it would be fine until the next period of similar revs.The answer ( hats off to Go Mog ) was to replace the alternator. The problem never reoccured. After I had sold my first 4/4 the new owner had the same problem and once again an alternator change solved it. Coincidence perhaps.

I had a curious problem like that with an old Morris J van back in the 60s.

It cut out every time we went up a long hill. It turned out to be an exhaust gasket leak at the manifold exhaust pipe junction. It was directing hot exhaust gas onto the fuel line. I actually went up the mountain backwards at the Bathurst race circuit, much to the bewilderment of the others in the traffic going up and the cop who was standing at the hairpin. Naturally I managed to fix it before driving back to Sydney