Honda-SOHC

SOHC.co.uk Forums => CB750 => Topic started by: Johnny4428 on August 06, 2025, 09:27:29 AM

Title: Ignition failure?
Post by: Johnny4428 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.

Title: Re: Ignition failure?
Post by: Johnwebley 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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Title: Re: Ignition failure?
Post by: Bryanj on August 06, 2025, 10:10:47 AM

More likely caps than coil

Title: Re: Ignition failure?
Post by: Johnny4428 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.