Topic: CB750 K4 (1974) New Ignition

[JeffK]

Guys, my #3 cylinder is not firing and it is because one of my ratty spark plug wires is literally broken. I need new spark plug wires but as you all know it's not that simple because of the wire/coil connection. I have read a lot of the threads here and I'm still confused.

What is the best avenue for my fix? Do I get a whole new coil/wire/cap combo or is there a way to purchase pre-wired caps and attache them to the existing coils? Or is there a better alternative?

Thanks guys

BTW - If you know a proven good coil/wire combo I would like to know it. All I am seeing is sketchy Ebay stuff.

[bryanj]

If you go to the UK site (sohc.co.uk) and look in alladdins cave one of our more electrician members(Ash) has written a how to repair the coils. Cheap, easy and fairly quick

[JeffK]

Thanks Bryan

[drumstyx]

There are 3 options here: replace the cables at fairly great effort, splice the wire (yep, there are splice kits for high tension wires), or replace the coils.

For the last option, you can either go used OEM, which will probably be cheap, or you can get a set of coils with replaceable leads, new wire, and a crimp tool (other than the coils, the crimper was the most expensive part for me).

For my money and effort, if I wasn't specifically keen on upgrading the system, and just wanted it back on the road, I'd probably just pick up a set of used OEM coils.

[JeffK]

Thanks for the response. Do you know if there is a way for me to attach new ends (caps) on the old wires? I know the coils work. The only real problem is that one wire/cap broke where the wire attaches to the cap.

Thanks again.

[drumstyx]

Thanks for the response. Do you know if there is a way for me to attach new ends (caps) on the old wires? I know the coils work. The only real problem is that one wire/cap broke where the wire attaches to the cap.

Thanks again.

OH! It only broke at the end? Yeah you can get new caps...heck, you might not even need to trim the wire back -- they just screw onto the end of the wire. Most would recommend trimming back to clean wire though. While you're at it, measure the primary and secondary resistances if you've got a shop manual and a multimeter. Definitely worth getting all new caps, they're like $3 each

[JeffK]

I should have been clearer but I am no wiz at this. I will show off even more of my lack of knowledge and ask where do I get these? Are they a specific size? I know two are bent and two are straight. I guess I'm asking if these things are universal or not.

Thanks again

[drumstyx]

NGK SD05F for the straight ones, NGK XD05F for the angled ones. Depending on where you get them, they're $3-$8USD each.

[Shtonecb500]

ngk straight caps.

[PeWe]

I changed the HT leads on my CB750 stock coils back in the 80's. Only for color.
I had red wire available at my job for free. Crimping tools and crimp sleeves.

I cut wire around 1 1/2" from coil, removed some insulation and crimped the new red wire. A little bit longer to have possibility to refresh ends when needed.
Crimp sleeve area covered by 2-3 layers of shrink tubing, also free.

Your coils are around 40-50 years old now and might have other issues?