Author Topic: Ignition failure?  (Read 2135 times)

Offline Johnny4428

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Ignition failure?
« on: August 06, 2025, 09:27:29 AM »
When I rode the 750 home at the weekend I definitely didn’t have 4 cylinders, No4 header was cold. So yesterday had a look at the usual - leads, plug caps, plug, connections etc. Could not find anything, except when I run with No4 plug out and connected I get a weak spark then nothing! I am at the moment suspecting a failed coil. I have done a resistance check between 1 & 4 leads, result nothing!
Going to check today with another multi meter. Could a failed electronic ignition have resulted in a fried coil? These are old original coils that I gave the Ash’s refurb with new leads and caps. I will resume the investigation today hopefully.
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1
1978 Honda CB550K3
1999 ST1100 Pan European 50th Anniversary.
1975,1984,1986 Honda C90’s
1973 Honda CB750K3
1977 Honda CB550 (almost)

Offline Johnwebley

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Re: Ignition failure?
« Reply #1 on: August 06, 2025, 09:33:07 AM »
Check the plug caps

Most have a resistor of 5k,

These can fail with age



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Offline Bryanj

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Re: Ignition failure?
« Reply #2 on: August 06, 2025, 10:10:47 AM »
More likely caps than coil

Offline Johnny4428

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Re: Ignition failure?
« Reply #3 on: August 06, 2025, 12:30:34 PM »
Very surprised to find I have a fecked coil. Have another temporary one fitted at the moment with a bit more resistance at 17k ohm. It is running great. I did find a questionable connection at the coil, the blue wire which is 1 & 4, not sure if this added to the coils demise. I will order a couple of new coils anyway.
1952 Cymoto on Triumph bicycle.
1961 Matchless G3
1974 Honda CB550K1
1978 Honda CB550K3
1999 ST1100 Pan European 50th Anniversary.
1975,1984,1986 Honda C90’s
1973 Honda CB750K3
1977 Honda CB550 (almost)