No spark at the plug? any ideas?

[super trimbo]

The pick up gave up on me this morning after coughing into live breifly with a bad misfire, now will turn over but wont fire.

Have done the following:

- Checked spark from the coil all okay, put lead back tested didn't fire.
- Checked spark from end of plug leads to block - none, so...
- checked points & rotor not burned/pitted/dirty and gap fine , so...
- checked the dizzy cap, which also seemed fine. Still wont fire so...
- I changed the dizzy cap & tested but wouldnt fire, so then i changed the condenser put it all back together + tested but still wont fire.

I'm all out of ideas at the moment, the only things I havn't replace are the points and rotor as they look brand new....

Anyone got any ideas?

[picky]

Did changing the dizzy cap give you a spark at the plug end of the leads? Also what condition are the spark plugs in.

[super trimbo]

Nothing I've done so far has given me a spark at the leads. As i said loads of spark at the coild none at the leads (spark plugs are in good nic)

[mogbob]

With the dizy cap off, ignition on ( handbrake on,in neutral ) if you flick the points with your finger, do you get a spark at the points ?
Is the little earth tag/ low tension wiring ( base plate to external side of distributor/ lucar connector ) sound ?
A little wiggle of the wire sometimes brings it back to life.If it works...order up a new one straight away.
Coil to distributor lead/connections sound ( wire.. White / black trace ).
Process of elimination but it's probably a duff rotor arm..got an old/ new one ( preferably a red top ) you can substitute/ borrow/ to test ?

Good luck
Bob

[bmcecosse]

Sounds like dodgy rotor - try an old one.

[super trimbo]

right then off the the shed it is to raid my spares bin, one of the half dozen dizzy I have must have a rotor in...

[super trimbo]

tried 2 diff rotor arms - no joy, also replaced the internal wire in the dizzy at it looked at bit grotty, still no joy

Dumbfounded!

[bmcecosse]

Swop a complete dizzy in if you have spare . But you say spark at coil - so I can't see where it's being lost on the way to the dizzy cap, down into the rotor arm, then out to the HT leads to the plugs........ Ht lead from coil to dizzy cap ok??

[super trimbo]

Thanks BMC,

As far as I can tell the HT is in good order - nice blue sparks jumed the gap between the end of the lead and block when testing the coild as per haynes manual.

Just to summarise:

- Points sparks nicely
- As does the coil
- All parts now replaced tested after each individual replacement (aside from the dizzy itself)

Could be something to do with th de arming switch dad wired in for me (to stop it getting nicked), so tomorrow thats my next port of call...

Have four or five dizzies knocking about (me and dad both have moggies) so i'm sure i'll get to the bottom of it eventually. I even checked if it was me being a bit dim ( i hadn't checked fuel supply) but fuel pump/carb etc all good , she wont even fire from easy start - But I guess without a spark she wont!

Dads back Wed so i'll get him to cast his eyes over....

[bmcecosse]

Hmmmm. If in any doubt about power feed - just run a temp wire from the battery directly to the coil. But you say sparking - so it is surely a matter of 'losing' the spark someway along the line from the HT lead to the plug....... Does the dizzy cap have the little carbon brush and the spring present? Is there definitely no spark at a plug when laid on the block and cranked??

[beero]

If it is a side entry dizzy cap are you sure the screw has cut into the ht leads okay?
You should be able to test them with a meter so long as you have copper leads.

[Stig]

If it is a side entry dizzy cap are you sure the screw has cut into the ht leads okay?
You should be able to test them with a meter so long as you have copper leads.

If they're resistive carbon leads they should still read a few kOhms on a meter.


I doubt it's the de-arming switch that's the problem, that would be on the 12V side which seems to be OK.

[kennatt]

try a known good spare dizzy and if you are certain that there is a good spark from coil lead to block,and that there is still no spark at plugs then it has to be the connection of the coil lead to dizzy can't see anything else.How are you checking the spark at the plugs,are you sure the plug is well earthed to the block sometimes it pays to clamp it on with mole grips.

[super trimbo]

Thanks for all of the input guys,

Turns out that although I checked the fuel at the pump end i didn't check inside the carb which was full of sludge! Now runs sweet again!

Cheers

Tris

[MarkyB]

Nice work!

[beero]

Well done. You have just disproved the old saying "most carburettor faults turn out to be ignition!"

[chrisryder]

the muck in the fuel still doesnt explain why there was no spark at the plugs...

at least you've sorted it and you're back on the road!

[picky]

If the boot on the spark plug lead is quite long sometimes the distance is too far for a spark to jump, even if everything is working.