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Discussion Starter · #1 ·
I have a 1972 cb350, which I've been trying to get tuned for the past year. I've been chasing what I thought was a carb problem, but I'm wondering now if it's electrical. It would give me poofs and hesitations which I interpreted as lean conditions. I've put on longer mufflers and changed jets until it's so rich it's fouling plugs. But I'm fouling plugs while still getting the hesitation.

So I thought maybe it's not a lean backfire, but just a plain old misfire? Timing is spot on, checked with a strobe. Valves are tappy loose. Carbs have run the gambit of settings from super lean to super rich, on both pilot and midrange, always with the hesitation.

I've generally dismissed the electrical as being the problem as all parts are newer, but I can't dismiss anything anymore. I went in again and checked all the connections and grounds (for the coil/condensers anyways). I ran another ground just in case from the coil bracket to where the battery grounds on the frame. I cut fresh wire and the plug boots are less than a year old.

Checking resistance, on the left I get 3.0 primary and 15.22 K on the secondary. Right, I get 3.0 primary and 16.3 K on the secondary. Secondaries are with boots on.

Are these numbers okay? Is it okay for the secondaries to have that difference?

I have my final licensing test in September, and could really use a solid running bike to boost the confidence.

Thanks,
John
 

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I'd start with a fresh battery in your meter, set it to the lowest resistance range and touch both test leads together, write down the reading, try it in the next range up as well, subtract this reading from all resistance measurements.

Unscrew your plug caps from your wires and measure their resistance separately, you may need a nail or screw long enough to reach the contact deep inside.

Then measure your coil secondaries again.

It never hurts to add extra ground wires, even directly from battery negative side directly to the points plate.

Also you could measure the voltage to your coils, perhaps with all of the old wiring and old switches your coils are getting less than battery voltage until engine rpms rise.
Some have added new relay-switched circuits to power their ignition systems in order to supply full battery voltage at all engine rpms.
 

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Make sure the battery is at full voltage, 12.7 is full. Hondas run like crap if the battery is down. Next is the coils, plug wires and caps. You said yours are newer, what does that mean? Next is the points. Are you using Honda points or aftermarket? Resistance measurements in coils don't mean much. You have to be able to check inductance to verifiy they are in spec. The CB450 DOHC FSM gives the required spark gap distance the coil must pass. It describes setting up an apparatus to measure the size of the gap size. TMI, just get modern coils, wires and caps. I like PAMCO ignitions.
 

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Discussion Starter · #4 ·
On my meter, the lowest is 200 ohms and touching the two probes I get 0.04.

On the boots, I get 5.34 (K ohms) on the left and 5.13 on the right. Without boots, the coils read 9.84 on the left and 11.15 on the right. Added up they're pretty close to the combined numbers above.

Battery is currently at 12.6. I forgot to put it on the tender last night after tinkering with it, but it was on before the last test ride. I'll plug it in now.

I was having some arcing from the left boot to the points cover last year, and replaced both boots then. Since then I would guess it's probably been less than 200 miles and a couple days of setting and resetting points.

I fried a set of new coils about three years ago after leaving them on, so the coils are a few years old (The kind like from Dime City or Common Motor that fit the bracket) and I've been religious about turning the key to off after short bursts of timing the points. The wires are the type that are fixed to the coils. I just cut an inch to get to fresh wire. It still looked good but it's an easy step.

Condenser was replaced by me when I started this project 7 years ago, but the bike never started for the first 5 years. So it's basically two years old, with probably less than 300 miles on them. Points are Daichi. Bought in a kit with the condenser, but were just installed in the past two months.

Checking through all my connections I found a green female in the cluster around the coils which is just hanging out. All of my electrical works, so is this an extra, like that brown one in the bucket? (That one made me crazy for a few hours.) 20180831_154451.jpg

Any leads with any of this information would be awesome. Thanks.
 

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So you've got a pretty good meter and the skills to use it correctly, you're already ahead of the game there.

I'd reassemble the lower resistance coil to the higher resistance cap, and the higher resistance coil to the lower resistance cap, just to help keep them as balanced as possible.

I wonder if the arcing from the old plug boot to the points cover could have damaged your condensers, or does the cover being on constitute a Farraday cage and your condensers are fine?

What plugs are you using and what gap?
 

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Discussion Starter · #6 ·
You had me at farraday cage.

I'm running b8's with a 0.03 gap. Swapped the boots and am starting to button it up again.

I've learned the hard way what wrecks coils. Is there something that wrecks condensers?
 

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Discussion Starter · #7 ·
Swapping boots didn't make a change.

Digging through a parts bucket I found some old condensers. Figured it was worth a shot and swapped them in. Misfiring side flipped from right side to left side. Tried to monkey up an arrangement which was entirely logical but probably broke every electrical law, to make two half condensers equal one good condenser, but in the end it stayed bad on the left side.

Ordering up a new condenser and hoping it solves it.
 
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Running points? If you use a cheap little continuity tester with a AAA battery inside, you can set your timing without ever turning on the bike's ignition switch. That eliminates any chance of coil melt-down. This will let you set timing on a project bike that has no battery installed.

Just sayin' ;)
 
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My 71 CB350 was causing me fits for a while. I replaced Points/plugs/condensers. The symptom was that it started and idled fine but could not get it above 7K rpm without a lot of coaxing and miss. Plugs read rich. Made sure the float level was correct and valve and ignition timing was spot on. Carb Sync was spot on. Then it occurred to me that I was still running old air filters. I didn't want to spring for $100 each for NOS so I cut off the old paper elements and replaced with strips of UNI bulk sheet green air filter foam (ebay). Running problem solved for $12 and an hour or so!
 
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