Morris Minor Owners Club

Hi
Thought I'd share my strange engine problem from the weekend.

Saturday morning, moved 'Basil' out of the garage as needed the tidy the far end a bit. Ran fine.

Saturday afternoon, started basil to put him away and he was running rough, sounded like he might have only been firing intermittently on 1 of the plugs. Thought I'd take a look on Sunday.

Will mention at this point that I've only had basil about a year and he had an Accuspark Coil/Dissy system fitted only a few years ago.

So Sunday morning, Basil won't start.

Did all the usual things, took the plugs out to dry and clean them, plenty wet with fuel so that wasn't a problem, checked for spark at all 4 leads and did think the spark might be a bit weak, but it was there.
Still nothing, not a hint of anything firing when turned over.

Took plugs out to dry them again and refitted....
This time, on turning over, tried to see the strength of spark at the top of the dizzy, i.e. from the coil. A good strength spark jumping 10+mm easily and Engine fires, even with that gap. As I move lead closer to top of coil to connect it, Basil stops.

Repeat process moving lead closer/further from top of coil and engine fades/picks up, stopping if lead is connected.

Had a good look at top of Coil and the end of the lead, couldn't see anything, bit of a wipe with paper towel, nothing was dirty, put back together and fires no problem.

Tried him again this morning, still firing and running fine.

Just cannot reproduce the problem.....

I've always had much the same issue with Max (no electronic ignition). He always needs a bit of choke for cold-starting. Starts fine. Move him out of the garage. Switch off. Leave for a while. Re-start... and runs on 3 cylinders but 4th picks up pretty quickly. If I do this a lot e.g. during the winter when he's just in and out of the garage once a week or so, misfire gets rapidly worse and soon reaches the point where he won't start. Plugs out. Always very sooty (not surprising with the use of choke I suppose) and no.1 wet as well. Plugs cleaned, gapped and refitted. Starts fine. A 10-mile run to blow the cobwebs out and all is well again... until next time.
P.S. I've not checked for strength of spark.

I would check the compression on all four cylinders. Does the radiator water level stay constant?

Since the fault cleared when you wiped the coil I think that must have been the problem. Even if the coil looked clean a tiny amount of moisture or conductive dirt could cause the spark to track away.

simmitc wrote: ↑Mon Jun 11, 2018 12:54 pm I would check the compression on all four cylinders. Does the radiator water level stay constant?

Yes, all that's fine.

ianmack wrote: ↑Mon Jun 11, 2018 4:38 pm Since the fault cleared when you wiped the coil I think that must have been the problem. Even if the coil looked clean a tiny amount of moisture or conductive dirt could cause the spark to track away.

Agree, but what was confusing was that it started to run with the air gap of some 10+mm (and that's just from end of lead to end of coil, so metal-to-metal gap from lead to coil must've been huge) but then hesitated as I moved the lead closer and stopped as I got it almost on.

But just tried it again this evening and still fine.

So, my thoughts... I've read about something similar on this forum before.... When you have an air gap the energy has to build up to a point where it actually has enough energy to jump the gap. As you close the gap the system needs less energy to jump the smaller gap until we get to no gap and no energy in this case.... I have no idea where your energy is at this point your problem is intermittent and we all love intermittent electrical problems. Because the problem comes and goes I would start by cleaning all terminals, I have a tiny wire wheel and a dremel for just this purpose, you may find a problem as you go... loose terminal or terminal loose on wire for instance. I would also check/clean all earth points, engine/body/battery. Following the cleaning, your problem may or may not return but I would feel happier about doing a longer run as and when I wanted. Good luck.

Thanks for everyone's comments.

The key thing is that it was happy to jump a big gap from Coil to Lead, but got worse as the gap reduced, which is contrary to all principles of electrical energy jumping gaps.
We'll see what happens from now on...

Think it's time to buy a rotor arm for your spares drawer (glovebox).
It is possibly tracking through to the mounting shaft, insulation braking down.
Had a similar problem 30+ years ago. Car started fine but died as soon as I got going on the road, luckily it was a slight incline so just coasted back home. I was going to work so took my mums car instead.
Next day it started fine.
Fast forward three months or more, was going home and was in a traffic jam and got annoyed by someone who should have waited behind a parked car, nowhere for him to go so was blocking my path. Anyhow when he was able to move I gave my car some beans as you do and it died adding to the traffic chaos. Got it towed home.
Found the cause was the rotor arm tracking down the inside to the shaft.
In your case, with king lead attached it has enough potential to brake down the insulation and giving it an air gap reduces the HT at the rotor arm so sees the normal route to the spark plug as the path of least resistance.
The rotor arm can be tested with the distributor cap removed and holding the king lead with insulated pliers near (3 or 4 mm) the brass section of the arm whilst cranking it should not arc.
Although wiping around to coil fixed it, you would have expected any tracking/current leakage to occur when holding the lead away from the coil.
The rotor arm may have self healed? Who knows, why did mine last another three months.
Regards John