Ignition coils

[JezzaPeach]

Having rechecked everything on the new DSS coils, the primaries are showing 3.4 ohms and the secondaries with new 5k ohm NGK caps are totalling 21.5k ohms (not far off your 24!) Would those levels cause particular symptoms?
The bike runs well apart from the occasional hot tickover stalling I’m investigating.
Many thanks again, having learnt a lot.

[deltarider]

Having rechecked everything on the new DSS coils, the primaries are showing 3.4 ohms and the secondaries with new 5k ohm NGK caps are totalling 21.5k ohms (not far off your 24!)

When measuring low resistances, in the 200Ω range, it's good practice, before you start measuring, to firmly hold the probes to each other, to read the internal resistance (see pic below). Usually it's around 0,3-0,4Ω, which means the actual measuring will result in a reading that will indicate a 0,3-0,4Ω higher resistance than it actual is.

Would those levels cause particular symptoms?

Mwah. The primary resistance is on the low side, which could cause extra pitting at the breaker points, as they switch a higher current. Standard is 4,3 - 4,7Ω. Was DSS open about they're being not standard? Could you post a link to them?

The bike runs well apart from the occasional hot tickover stalling I’m investigating.

Owners of a CB500/550 should be aware of a typical weak point: the plugcaps. They're weak in two aspects.
1. They're exposed to rain and wind which effects their reliability. As a matter of fact, in the 42 years I own my bike there's been only one occasion, I didn't make it home. In torrential rain, they and/or the HT leads got soaked and the engine died.
2. GND (ground) is often all too close to the HT leads and/or caps. Checking is simple. Have the engine run in the dark and watch closely if you see arching between the plugcap and/or HT lead to the head. When concentrated, you can even hear it spark, which means that the spark you've witnessed, has not been delivered in the combustion chamber.
Another simple test is to check the condensers are not leaking. Faulty condensers may cause arcing as shown in the vid: https://www.youtube.com/watch?v=t3cuvGVwnjI At the breakerpoints a bit of sparking is normal, excessive sparking or arcing is not good and can indicate a bad condenser. In this vid the left condensor (1+4) is bad, right condensor (2+3) is good.
Video: courtesy Ulf Penner
Whilst you are there, also see to it the forked connectors at the back of the breakerpoints are not accidentely grounding to the plate. This can be intermittent! Especially the 2+3 breakerpoint has its connectors dangerously close to the crosshead nearby.
BTW, are you familiar with Ohm's law? I have a very simple and practical formula related to your bike, which will make it clear and impossible to forget.

[Sesman]

Static measurements are on thing, but operation under load is another. In other words although the ohmic resistance measurements indicate healthy conductivity and windings, it’s not a good indicator of conductor insulation quality as this breaks down with age and use leading to leakage/tracking and ultimately a weakened or complete loss of spark. I’m pretty sure Ash built a test machine to test the coil functionality at both frequency and voltage?

[deltarider]

Actually some time ago I'va asked Ash if I could build a simple one myself. Might be to complicated, though.

[JezzaPeach]

Many many thanks both for your time. Condensers are good. I will monitor over time and check the points for degradation. Some great learning points, one of the pleasures of ownership and restoration.

[deltarider]

Could you post a link where DSS advertises the coils you have?

[JezzaPeach]

Sure this is it:
https://www.davidsilverspares.co.uk/CB500K1-FOUR-1972/part_83526/

[deltarider]

Thanks. I believe it's the same product CMSNL offers: https://www.cmsnl.com/honda-cb500k1-four-england_model14660/coil-rlignition_30501300003p/
A few comments if you allow me. It's a generic product. Colours and gender of the primary leads is 50% incorrect. Both NEG wires are yellow. One should ofcourse be blue, but that's a detail I could live with. The connectors at the NEG wires are male, but should be female. Crimping connectors is an art in itself. Don't ask me how I know. On the plus side, I would not mind the spade connectors yours has at the coils.
More important however: the resistance of the primary circuit should be in the advertisement. When not in the advertisement, it should at least be on the package it is in, so you could return it unopened. Some retailers will not accept returns of electric equipment once opened. When neither is there, for me enough ground to return them. It would be merely out of solidarity with other customers. They should not have to guess. I have no less than four multimeters, one upstairs, one in the garage and two onboard my yacht. Failing to publish the primary resistance, could be for a different reason: the manufacturer cannot guarantee a precision within a band of let's say 0,5Ω. Manufacturer is most likely located in China. 

[JezzaPeach]

Many thanks again.