Topic: cb550 coils dilemma

[Bru-tom]

Hi guys, i have a question about my 76 550f1.

I now, after rebuilding the sucker, see that the coils are not assembling together as my mates ones. The numbers on the coils say FL807-6v. That 6v doesnt seem right, right?

I do have a spare set of coils, not sure if they work though, their numbers are FL703-12v.

How do i test these?

The bike did run on the original 6v ones. So i am not sure if i must worry about them not mating and joining together nicely.?


Any advice is appreciated.

[Deltarider]

For the original TEC FL703 (Toyo Denso) coils, Honda’s Shop Manual CB500-550 (p. 89) will show you how to check for continuity.
Primary coils should read 4,5 - 5 Ω, secundary coils (via HT leads, caps removed): 14-15 kΩ . Ultimate test however is to be performed on a testbench, which few of us have.

Aftermarket suppliers generally advise 5 kΩ plugcaps. That is more than enough for noise suppressing.

Years ago I swapped my OEM coils for the 3 Ω Dyna coils. Can’t say that I’m impressed. In spite of it’s high price, one already gave up after 30000 kms. The original TEC coils served me over 70.000 kms and are still O.K. On the other hand, HT leads in OEM coils are not impressive either. But that can be helped. Every time you pull the plugcap, there is a good chance leads can become loose. Removing the cap, cutting a bit of the end of the cable, screwing the cap back on can help, but eventually you’ll end up with a short lead. When it becomes too short – ta-ta-ra-ta -, you can buy he NGK J-1 cable coupler.

Like coils, condensers can live very long indeed and like coils chances are little they brake down at the same time. With it's wire detached from the breakerpoint you could check their isolation. When resistance is above 5 kΩ isolation is good, between 1 and 5 kΩ satisfactory and below 1kΩ it is bad. Test to be done after decharging the capacitor!
IMO most ignition related problems have their origine in deteriorated connections and/or fouled plugs.
It's not impossible your 6V coils work. A coil is a pretty stupid thing. Don't let Dyna mislead you with staggering 30.000 Volts. It's for the American market where quantity sells for quality. Your coils will fire well below 9.000 Volts since they've no choice.

[Bru-tom]

thank you kindly for the info and advice mate!

But why did my bike have the 6v coils and it ran okay the one time i rode it?

[Deltarider]

It's about the ratio of windings. The OEM coil for the 500/550 has 420 primary and 13.000 secundary windings. If your 6V coils can handle 12V input, there's no reason why they couldn't transform the 300-400 Volts of your Kettering system in more than 9.000 Volts, provided the winding ratio is at least 1:30. Again, a coil is a pretty stupid thing that's left no choice.

[Bru-tom]

thank you once more. i will measure them both and see where i stand.

Like i said the 6v ones worked, but now i am not getting readings on some of HT leads and incorrect low side ohm readings. i will confirm tomorrow when i use a proper DMM.

[Bru-tom]

it also turns out that the 6v coils i was using had 10k plugs on the end of the HT leads...

[Deltarider]

I do have a spare set of coils, not sure if they work though, their numbers are FL703-12v.

I'm pretty confident they'll work.
You could do this test. With a 12V battery (and a condensor) you can mimick the original set up. Just position the ends of the two HTleads face to face so to speak with say 7mm open space between their wires. You can shove them in a piece of transparent plastic tube for that matter, so the ends are nicely in front of each other. Connect the black/white wire to the + of the battery and then touch on and off the negative pole of the battery with the blue (or the yellow) wire. You may want to connect the condensor in parallel for best results. Check the wiring diagram for that and you will understand. Every time the blue (or the yellow) wire comes of the negative pole, you should see a spark jump between the ends of the HT leads. In principle the coil works when spark occurs. Then there's still a chance that they'll fail when well warm, but that can only be tested on a special bench or in practice riding.
I don't rule out 500 and 550 originally had close to 10KOhm resistors in their caps. As a matter of fact I found at least one some 30 years ago. I was advised by Honda Netherlands to have them all 5KOhm. Personally I don't see the advantage of 10KOhm over 5KOhm. I doubt it has significant effect on spark duration. In principle with 10KOhm more energy is lost in heat.

[Bru-tom]

thank you so so much Mr. i really appreciate the time taken to explain in detail your procedures an findings

i will test them as soon as i get a chance. where would i connect the condenser? between the yellow wire and the - terminal of the battery?

[Deltarider]

Tricky - I hope my English is good enough. The body of the condensor should be connected to battery negative and the wire should contact on and of together with the yellow wire also battery negative. 
For the principle you may consult http://oldmanhonda.com/MC/wiring500.html
(Click next and cancel all but coil.)

[Bru-tom]

then what is the point of connecting the condenser if the case and wire is connected to ground?

[Deltarider]

The condensor has three functions and acts as a buffer the moment the points open. To get familiar with the principle of the battery-coil ignition I'm sure Wikipedia or similar sites can provide you with all the information in better English than I can..

[Bru-tom]

well, i did the test but without condenser connected, so i wouldnt get a strong spark, but both of the 12v coils worked, now i also read 14k on HT sides and 5ohms on primary.

Could the energizing have brought them back to life?

[Deltarider]

My guess is they were still OK. 14KOhm secundary is good, 5 Ohm primary is fine, so they can't but work. Maybe they were discarded for their HTleads being too short. That can be helped by using other plugcaps or by the NGK J1 cable coupler.

[Bru-tom]

yeah! im so happy! i dont know why i was never reading the 14k before,but who cares, its there now hahahaha

the one HT lead is a little loose in the coil housing, can i put some silicon there to prevent any moisture from entering?

[Deltarider]

yeah! im so happy! i dont know why i was never reading the 14k before,but who cares, its there now hahahaha

My guess you didn't select the right range.

the one HT lead is a little loose in the coil housing, can i put some silicon there to prevent any moisture from entering?

They are somewhat loose from new. Nothing to worry about. You could do some silicon. I never bothered.

[Bru-tom]

its auto, it measured M-ohms, which is shy i was concerned.

Cool cool, Thanks you so much for your help, you're like my one man band!

thanks again