Lacking that certain spark

[onion]

Hi,

My battery had run flat, due to sitting, but when I tried jump starting her she ran at idle for about 5 minutes before suddenly dropping out (both cars still connected, donor still running).

On inspection I no longer have a spark at the plugs (or HT leads). I've checked through and have a spark at both the points and the coil, and I cant see any cracks on the dizzy cap.

Can anybody help me?

[katy]

have a spark at both the points and the coil,

If you have a big spark (compared to a weak spark) at the points it usually means that the condensor has failed.

[onion]

Unfortunately its a little spark at the points. The condenser had occurred to me as well, so I've swapped it out for a spare (brand new) Lucas one I had and it's the same situation.

[simmitc]

Rotor arm. Condenser - unfortunately new Lucas stuff is simply badged and often bodged rubbish.

[bmcecosse]

Odd that is ran - and then stopped. You SURE it has fuel getting to the carb? If you are sure there is no HT spark - then HT 'king' lead /rotor arm/dizzy cap must be suspect.

[onion]

Yeah, I found that very odd as well, and why I assumed it was not purely due to low battery.

The spark I was getting at the coil was from the king lead going from the coil to the body, so I assumed both of those were fine? Unless I'm missing something I seem to have chased the fault somewhere between the dizzy cap and the HT leads, but of that I've switched out the points, the condenser and the LT/insulator. I can't see anything cracks or tracking on the cap and find it fairly implausible that all 4 HTs would fail at once. And the rotor arm is relatively new (though I will admit I haven't tried swapping that one out as I didn't have a spare one on hand)

There is fuel in the float chamber, and I'm getting a ticking from the fuel pump so I assume that's not a problem, and this was a sudden stop, rather than a splutter or fade which I understood was a sign of ignition failure rather than fuel line?

[simmitc]

There was a batch of rotor arms that lasted for as little as 20 miles, or maybe 300 on a good day. If you fitted one of them....

[bmcecosse]

Exactly - fit an old rotor arm....and check the little spring loaded carbon brush is present in the dizzy cap.

[onion]

Sorry for the delay in reply, today has been the first chance I've had to look at her since I posted.

My battery is now fully charged and it turns out the rotor arm was partially to blame, so I'm now getting a weak spark at the plugs. unfortunately too weak for the engine to fire though. Seeing as its an equally weak spark at the coil as well, could that be the problem? (I know it's never the coil, but this is a modern replacement coil and therefore no where near as reliable as the old ones)

[bmcecosse]

If there is a spark - it should run. Try the jump leads again!

[onion]

We have lift off!

having now replaced everything in the dizzy and upgrading to the high quality condensor and rotor arm, along with a new lucas coil and a clean up of the earth on the battery, she started running.

I didn't get a chance to actually drive her, because of a 'pfft' sound coming from somewhere in the engine bay when I tried the the throttle, but I doubt that's electrical somehow.

[bmcecosse]

Don't rely on that 'new Lucas coil'.......fit the old one, and by all means carry the 'Lucas' (it's not really Lucas as we used to know it..) as your spare.

[onion]

I wasn't replacing an old lucas, I've never had one since I've had this car (replaced by a previous owner I assume), I was replacing a pattern one.