Cough, cough

[rgh0]

Sounds like you have a high resistance join in the ignition power supply somewhere to see 10.8 volts under load at the coil . If that is the voltage the Powerspark module is also seeing then it would not take much more of a voltage drop for it to stop working.

The high resistance is probably in a wiring join and it may go higher as the join heats up due to the resistance causing the miss firing

I would remove as many variables as possible by hard wiring the ignition power supply to the coil and Powerspark module from a known good supply point ( e.g. the main starter cable) and a known good chassis earth and seeing if the problem still occurs

cheers
Rohan

[Robbie693]

Thanks Rohan,

Good idea, I'll try that. They do suggest that the ballast system is bypassed for the Powerspark so I was thinking of running a new wire from the ignition switch but you've just made me realise of course the switch could be the problem too.

So -my electrical knowledge is fleeting- if I take the feed from the battery side of the solenoid this would result in a permanently live ignition correct? If I took the feed from the other side of the solenoid would that work or only when the starter was engaged?

Robbie

[alan.barker]

The other side is only for the 12 volt feed to your ballast coil 9v for easier starting.
Alan

[Spyder fan]

change the pump jet washers https://www.ebay.co.uk/itm/WEBER-DCOE-C ... XQI5tRh1Oh

I had this problem years ago, same symptoms.

[rgh0]

Thanks Rohan,

Good idea, I'll try that. They do suggest that the ballast system is bypassed for the Powerspark so I was thinking of running a new wire from the ignition switch but you've just made me realise of course the switch could be the problem too.

So -my electrical knowledge is fleeting- if I take the feed from the battery side of the solenoid this would result in a permanently live ignition correct? If I took the feed from the other side of the solenoid would that work or only when the starter was engaged?

Robbie

Yes you will have a permanent "on" ignition until you can get under the bonnet and pull the wire off the live main starter cable at the solenoid. Maybe sensible to run the wire into the cabin with a temporary switch and back out to the ignition so you can switch the engine on and off while testing in a hurry if you need to.

If that solves the problem then you need to get into the full ignition wiring circuit to find the fault. if it does not then the fault is not in the ignition wiring itself and maybe in other ignition components or carbs or fuel supply. However the 10.8 volts you measured at the coil under load suggests its in your wiring. If you do the temporary wiring setup measure the voltage under load in the same way and it should be close to the battery voltage

cheers
Rohan

[Robbie693]

Thanks guys,

I'll pursue the voltage drop first before looking into the fuel side and report back

Cheers

Robbie

[Hawksfield]

Robbie

To my knowledge the ballast resistor on your model plus 2 was a small circular resistor attached to the + terminal of the coil with two terminals.
The wiring diagram from chassis 72050732L shows this resistor and the connections, if you would like I could scan you the section from the manual
therefor you should not find any "in the wiring resistor" on your model, look for earth and connection problems !

Good luck

[Bigbaldybloke]

Remember that the power wire to the coil goes via that nasty little anti theft switch in the glove box, mine gave problems similar to your misfiring and once I?d bypassed it by soldering the wires together it sorted the problem. Check also the earth braid wire from the engine to the coil, is it in good condition and has clean connections at each end. Sounds to me like you have two problems though, ignition and fuel which combine in certain circumstances, misfiring due to ignition and hesitation and fuel smells due to carburation problems.

[Robbie693]

Thanks both,

The car was re-wired so I think the anti-theft switch is long gone, at least I never saw it when I had the dash out last.

I have a wiring diagram and noticed the ballast which I think in reality is a small ceramic disk, as I don't have one of these I assumed it had been removed of it's ballast system, which is why I haven't until now tested for circuit resistance. At least I now have something empirical to chase rather than some random symptoms.

Once I find my missing volts I can start playing with the carbs again!

Robbie

[Robbie693]

This is going to be a drawn out process and I don't know if I'm doing it correctly but bear with me...

First off I ran a cable from the ignition switch to the coil thereby bypassing the loom white wire. At the ignition switch the white wire loops through from the fusebox so there are two wires into one connector so I used a piggyback on my temporary wire so I could maintain the fusebox feed (right?). Anyway with this bypass installed I repeated the resistance test and got 10.9V so still some resistance somewhere.

Then I just directly connected a supply from the solenoid to the coil and I got 12.0V. Battery voltage during the tests was 12.7V (Perhaps the missing 0.7V in this case is due to the temporary coil earthing wire?)

Just to check the main battery cable I tested the voltage between the battery and the solenoid and that was the same 12.7V as the battery itself.

So what do I test next?

Would it be the white wire from the fusebox to the ignition switch - I don't really know if this would affect my issues as I think the power comes in to the ignition switch via the brown wire... I'm at the limits of my understanding here!

In the meantime I've ordered some washers and seals for the pump jets (Dellorto) as per Alan's recommendation

Robbie

[alan.barker]

A ballast resistor is only for cold start to have 12v to a 9v coil.
General running i see no advantage
Alan

[Bigbaldybloke]

The basic route of the normal power to your coil goes from the battery to the starter solenoid, from there to the ignition switch, from there it goes via a loop on the Rev counter to the anti- theft switch in the glove box then to the left hand side of the dash where the dash harness is joined by bullet connectors to the front wiring harness and ends up at your coil. If your anti theft switch has been removed, check how it was done, are the wires just twisted together, soldered, crimped or whatever. The only other potential points for a bad contact are in the ignition switch itself or the bullet connectors where the front and dash harnesses join. There is not a fuse in this circuit.
As for a temporary feed, the white wire it sounds like you have connected to is again fed from the ignition switch and goes to the fuse box where it feeds mainly the instruments via the plain green wires.
As this white wire still has the low voltage problem it tends to point to the ignition switch or the bullet connectors being the problem.
As already suggested, take a wire from the battery connection on the starter solenoid into the car via a switch and back out to the coil. You can either replace the existing coil power connection or piggyback this additional wire on to it. If you piggyback it you can try switching the new supply on and off while driving and see if it fixes the problem. Hope this helps.

[Robbie693]

Thanks Mr B, yes that does help a lot. I thought the white wire went straight from the tach to the coil. I'm going to have to do some digging behind the dash to find those bullet connectors.

I did do a wire straight from the solenoid to the coil but without the switch in the car as I was only checking voltage - not actually driving it to check for any effects. This is something I should do next.

With a new replacement loom, is the wiring still present for the anti-theft switch?

Robbie

[Bigbaldybloke]

Don?t know if new wiring harnesses have the anti theft switch included, if they are sold as a direct replacement they should have. A quick phone call to the supplier should get you the answer.
Unless you have lots of electrical problems or want to replace your dashboard, personally I wouldn?t consider replacing the dash and front wiring harnesses just for this problem. The bullet connectors are on the left behind the glove box if you are on a rhd car, they should be tight to get apart and will probably look a bit discoloured and grey when you get them apart. They can be cleaned with fine abrasive paper and if the connector blocks are corroded or don?t hold the wires in tightly then replace them, try to get good quality replacement connectors as some on sale are apparently poor quality, I?ve bought some recently which were advertised as genuine Lucas and they seem fine.
Replacing a wiring harness sounds simple but is a time consuming job if you do it right, even when you have the dash out on the bench, and a new harness beside it, it can be a daunting task to swop every thing over, secure it in place and replace the dash and all the trim you have disturbed. If it is a problem with the wire and not the ignition switch or bullet connectors, I?d be tempted to loosen the dash and lean it back in situ to give access to run a new wire from the ignition switch via the tachometer and out through one of the bulkhead grommets on the right hand side to the coil as this would be the shortest simplest route and could be made to look neat and almost out of sight with a bit of careful route planning. Even doing this will need you to drop the steering column, disconnect the bonnet catch, choke cable, eyeball vent pipes and more, unless others have found another way for this?

[billwill]

A ballast resistor is only for cold start to have 12v to a 9v coil.
General running i see no advantage
Alan

Not quite... The heavy load from the starter motor will bring the voltage from the battery down from 12 volts to say 10 or 9 volts due to the internal resistance of the battery.

So the coil is designed to operate at this lower voltage (for easy starting), but that would cause it to be fed with too many volts during normal running (causing eventual failure) , so during normal running the coil is fed through a ballast resistor to bring its supply down to its design voltage.

This means complicating the wiring and the most practical method is to have an extra contact on the starter solenoid, which is connected to the battery ONLY when the solenoid is operated. This extra contact goes direct to the coil, hence bypassing the ballast resistor.

Other circuits which might be considered would probably require a diode to prevent a back-flow of electricity (through the starter motor) and the volt-drop across the diode would defeat the whole purpose of the system.