Topic: 1975 CB400F ignition problems

[chrisp]

Hey all.

So, my bike has generally been bulletproof for over a year, but has been giving me a lot of (I believe electrical) issues lately and leaving me broken down on the side of the road.
It was set up after I bought it by a vintage Honda specialist shop in CA a couple years back. It was put onto an electrical ignition, amongst a slew of other upgrades. I also put in a new modern regulator / rectifier over a year ago.

A couple of weeks ago, I took the bike out and it instantly started running like #$%* around the corner from my house. It was bucking, giving very inconsistent power, and would die if I tried to let it idle. It also backfired a bit, sounded like it was running out of gas....none of this I'd seen before.

Took it to my local shop, and my mechanic couldn't duplicate the problem until the second day of riding the bike...but then it happened exactly the same. He tagged the electrical ignition as the problem, and switched me back to points.

That was about 2-3 weeks ago, and until yesterday the bike was running great. A little stutter here and there, but I think that's just due to the points vs electrical.

Now it's back to doing the same thing as before. It starts, but wont idle, plugs are getting wet, so clearly not combusting properly, and is super inconsistent power wise again.

Any idea what this could be? The thing that's super strange to me about all this is how it was running fine and then went back to this same problem. Feels like I have a ghost in the machine.

I ordered a Dyna ignition which I'll install when it arrives, but I want to rule out anything else.
I've heard coils are very rarely the problem. I also have the bike on a Lithium Ion Shorai if that might be a culprit.

Any suggestions / help would be greatly appreciated.

[NobleHops]

What's the resting voltage of the battery, and what does it read at some nominal RPM like 4K?

[Matt Chapter]

Bad fuel? Too much ethanol?  Are you using a fuel filter? How's the air filter? When was the last time you did the tune up including valves, carb sync, etc?

If the bike will start (assuming you're using the electric start) the battery is at least ok enough.

[MoMo]

First thing I would do is check all ignition electrical connections-black/white, blue and yellow wires.  If it is the same as before when the points were put in maybe a connection was temporarily fixed and then came loose again...Larry

[chrisp]

Thanks for the tips.
I've checked the wiring and things look good there.
Fuel is the same I've been using forever. Premium Shell. I have a fuel filter, and I just replaced it just in case.

The points were set up recently by my mechanic, and I really dont know much about setting them yet.
The contact points do seem very close.

I talked through it some more with my mechanic, and I'm going to try swapping out one of the coils.
It seemed to me when checking for spark on all the plugs, that 1-4 were weak / inconsistent , and 2/3 were ok.
Hardest part now is diagnosing..I'm really unsure how to diagnose problems and where. The coils look to be ok as far as resistance. 4.8-4.9 ohms from both.

[dave500]

if its starting on the electric starter ok i guess the battery is ok,even though i dont like those batteries,whats the plug cap resistance like?

[Matt Chapter]

If you've still got the points on there, adjusting them is a piece of cake.  Just follow the procedure in the manual.  Failing that, if 1/4 are still weak I would swap coils..  You're on the home stretch of troubleshooting.