Engine earth, starter motor drawing too much current and dropping the battery voltage too far, crook battery connections, to name a few.Also, a stronger spark is needed for very rich and very lean mixtures, so it's possible that the spark is OK, but the mixture is way out.You mentioning the CAS is interesting - I wonder if the timing is way out on cranking, which would cause poor starting too?
You know my situation Dave...... but engine earth is fine, I have connected extra earthing and no difference. Battery connections are new. Looks like I do have a weak spark when my car doesn't start though Dave. Removed a coil pack and attached a spare plug I had to it to check spark. Cranked it and barely had a spark. All of a sudden spark become very strong and she fired easily using only 5 cylinders. I am also finding that after cranking it for a while when it doesn't want to start, that finaly when it does start the alternator belt slips badly like there is alot of strain on it. I have tightened it up, and sprayed it with some of the belt grip spray but still slips when cold. I guess it is still possible that I haven't tightened enough and it's not related, but I don't think so.
Hmmm, will have to have more of a think about your situation, if it's definitely spark. The reason tha laternator belt slips after cranking over for a while is that the battey is depleted, and the alternator is running at its maximum capacity to try to recharge it. This oputs a much larger load on the alternator belt. If it stops after a few seconds, then I wouldn't worry about it. What are your plugs gapped at? Might be an idea to try smaller gaps to see if it starts when it is cold, or try some copper plugs in it.
