New vac unit fitted but now no spark.

[timjsparrow]

What ho all.

I have been having a problem with hesitation on acceleration and having read through previous topics on the subject and all else being as it should be I concluded that it was a dead vacuum unit.

I have now replaced the vacuum unit, with the dizzy in situ, and all other parts are as they were before the new unit was fitted, but she won't start.

I've got fuel and she'll turn over but I have no spark at either the points or plugs. The settings on the vac unit are as they were on the old one. I've tried new points and rotor arm (I use the red one) to no avail and swapped back to the old ones but still no joy.

I only replaced the condenser as part of her service a few weeks ago with a Distributor Doctor one. However, it is the one thing I haven't tried changing, but she was running well before the hesitation problem a couple of days ago.

Any ideas as I've run out of them at this point?

[myoldjalopy]

Mmm...OK, no spark at the plugs - but is there one at the end of the king lead? Worth checking as the other thing you haven't mentioned changing is the dizzy cap...Otherwise, maybe a wire has got loosened when you fitting the new vac unit - at the coil or at the dizzy (there's also a little 'tag' wire in there that connects to the points that can get broken). Double check the points are fitted correctly so that they are not shorting out and that they are gapped correctly.

[timjsparrow]

No spark on king lead either, points gap spot on at all revolutions and appear to be fitted ok. The dizzy cap and HT leads were new about 2 weeks ago and have been working fine. Would it be worth changing to an old set that I know works (kept in the boot for emergencies) and see if that makes a difference.

I know its never the coil, but I've changed that anyway just to rule it out and no difference.

[oliver90owner]

Check for current through the coil when the points are open? Check for current when they are closed, too. I expect that will tell you something, if ‘nothing else’ should have changed

RAB

[myoldjalopy]

If there is no spark at the king lead then the dizzy cap, leads and plugs are probably OK and the problem is further back down the line.
Check for 12v at the SW connection on the coil, ignition on. If OK, remove the wire to the dizzy at the CB coil connector and test for 12v at that coil terminal. If 12v, replace the CB connection on the coil and test for 12v at the other end of this wire, detached from the dizzy. If you have 12v there, the problem is almost certainly in the points set-up. This can be confirmed by connecting a 12v test bulb between the dizzy end of the CB wire and its connection point at the dizzy, and opening and closing the points on the starting handle slowly - the bulb should then flash as the points open and close.
As you have tried replacing pretty much all of the ignition components (other than the dizzy itself) I'm beginning to think its a wiring/connection fault. Let us know the results of the above tests and we can help further.

[don58van]

Hi

I suggest that you check that the so called 'pigtail' wire from the side of the dizzy to the points is in good condition and making proper contact. While you are there, make sure that you reassembled the points correctly. A common mistake is to put the plastic insulator bush/washer in the wrong position.

I hope you get it sorted without too much more frustration.

Don

[myoldjalopy]

Just to avoid any confusion, the 'pigtail' wire Don refers to is the same as the 'tag wire' I mentioned earlier, and, indeed, it may be the problem, particularly if the above tests show 12v is reaching the dizzy. It is almost certain to be a simple fix once the cause is identified through systematic tests............if the battery is turning the engine over OK, no spark means a fault somewhere in the low or high tension ignition circuits.

[timjsparrow]

She lives! Looks like it was a combination of me putting the insulation washer on the wrong side when I put everything back together the second time in the dizzy and a Chinese Lucas coil on it's way out.

Put the wires in the dizzy back on the right side of the plastic washer and bunged a new Bosch Blue coil, recommended elsewhere on the forum somewhere as a good coil, and she sprang into life first turn. She's a tiny bit lumpy but I think that's just down to some timing adjustment needed. No more missing in high revs though.

Main thing is she runs, so I can now get her down to Ian Allen's at Ely for a fine tune. He's a wizard when it comes to getting her running sweetly.

[myoldjalopy]

Great, glad its sorted and thanks for coming back with the outcome. Too many threads fade out before we learn what the resolution of the problem was.