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Discussion Starter · #1 ·
And so the problems continue.After sorting out my carbie problems,i now find that I have no spark at the plugs.I have cleaned the points and set timing etc,and get a reading of 12 volts at the movable point. However if I hold the spark plug against the engine there is nothing .I get a reading of 5ohms between the primary coil wires and a reading of 14k between the secondary wires, but infinity between the primary and secondary.not sure what all that means, has the coil had it?

any help much appreciated.

Thanks Graham

CB 175k3
 

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Graham,
I've run into a similar problem with my new/old 1972 CB450, and I've narrowed the problem down to the plug wires and plug caps. My plug caps are the resistor type that have an embedded 5K ohm resistor, and both caps are showing infinite resistance between the wire input stud and the plug clip. This is not surprising since they're 46 years old, and I've ordered a new set of coils (since the plug wires are molded into the coils) and new plug caps. One of my plug wires (left cylinder) had a broken core conductor about an inch from the plug cap. If your coils, plug wires, and plug caps are still original equipment, I'd suggest you look closely at the plug wires and caps. It's easy to overlook them when troubleshooting ignition problems.
 

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Discussion Starter · #3 ·
Hi Chilimac,

Thanks for your advice,i will go and buy two new plug caps today,before I order a new coil. I found a couple of videos on the internet showing how to test a coil with a multimeter, but they both seem to contradict each other.I asked at the local Honda dealer but he said the Cb175 coils are not available anymore, so I shall look on ebay.
once again thanks
 

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Graham,
My new ignition parts are supposed to arrive in the mail tomorrow. I'll let you know if they cure my problems.
 

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Twin fire coils ( like 175's) aren't like normal auto coils they're more like transformers there should be no continuity between the primary and secondary
Your coil numbers seem fine
The coil fires when the points open ( no continuity going to the points )
I'd get a new set of plugs and caps
 

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Graham,
I've installed my new coils, plug wires, and plug caps, and I get spark at both cylinders, but it's still a wimpy spark, not hot enough to start the fire. The only thing left from the original ignition is the points, and I've ordered a new set. In the meantime, I've looked at the dwell time of the old points, and it looks like the cam followers are so worn out that I'm only getting about 10 degrees of dwell (this is an eyeball estimate, not a measurement.) So I should amend my earlier suggestion to you about what to check/replace and include the points! After all, they're cheap.
 

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Discussion Starter · #8 ·
hi Chilimac,

I determined that my coil is ok, and then I got a large paperclip and put it in the plug cap and that then produced a thin yellow spark against the engine casing. I took off the cap and put the end of the paperclip straight into the plug wire and got a nice fat blue spark, so I shall order two new caps and may as well get new plugs as well.My points are fairly new.My plugs are overrich and sooty,so that's the next problem to fix,one thing at a time though.

Good luck with your bike

Cheers Graham
 

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Graham,
Sounds like you're definitely on the right track. My new points haven't arrived yet, but I've discovered a possible problem that I'll be checking out. The wiring diagram for my CB450 shows a ring connector attached to a frame-mounted ground stud to provide a central chassis ground bus, and there's nothing connected to my ground stud. Last night I was cranking the motor with the points cover off and noticed I was getting a nice spark across the points - which the new condensers are supposed to prevent! It leads me to believe (and hope) that restoration of a solid chassis ground will enable the points, coils, and condensers to do their job correctly. I have to remove the gas tank to get at things, and that's a bit of a pain with the 450.
 

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Well, you never know what you don't know until you find out. I got new points into my CB450 today, and they didn't help at all. So I called my Honda guru friend, and he suggested that I check to see if the points cam was installed in the advance mechanism 180 degrees out. I didn't realize that was possible until he described how to reverse it, and that turned out to be the whole problem. The bike is running again, on OEM points & condensers. Recall that when I got the bike, it had a PAMCO electronic ignition installed so that it didn't need the cam or the points, and apparently the man who installed the PAMCO took the advance assembly out to clean it and put it back together with the cam 180 out.
I know this post is largely out of place in this section of the forum, but I just wanted to close out the thread from my perspective (and it may be useful to someone else having similar difficulties.)
 
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