Topic: 1978 CB550 Only Firing on Cylinders 1 & 4

[exponent]

First Post! My 1978 is only running on two cylinders. 2 & 3 do not fire. I checked both coils and they are fine. The spark plugs are foul but the middle two are not worse than the other two. The wiring loom was rebuilt last year by ACME cycles in Chicago, they also replaced the reg/rec. When i tested the leads, both yellow and blue wires, I had no resistance. Not sure if related but the SP15A fuse is missing. Any help is appreciated, this is my first bike and (kinda) my first project and I would love to get on the road soon.

[FourUsTry]

Condenser or points for 2-3?

[RAFster122s]

What kind of meter did you use for testing the wires? Cheap meters are notoriously prone to not having the accuracy or sensitivity to measure small resistances. If it was a cheapo/free Harbor Freight meter, then that is part of your problem.
What exactly was "rebuilt" in the harness? Was the bike running last year after they finished their work?
Why is the fuse missing? Is the fusebox showing any signs of melting around the terminal ends when viewing the back side of the fusebox? They can overheat causing the terminals to become loose and cause problems.

[Deltarider]

Intermittent arcing of the plugcaps/HTwires to the head can cause problems The CB500/550 is prone to this. Best seen in the dark. Plugcaps should be firmly attached to their HTwires. Grounding (intermittent) breakerpoints and faulty condensers can also cause problems. In case you have the stock ignition setup, I'd first check breakerpoints and condensers. Open the ignition cover. First check if breakerpointgaps are still correct and also that the forked connectors at the back of the breakerpoints are not accidently touching the plate. Then, with engine running, see if there's excessive arcing at the breakerpoints. A tiny bit of sparking is normal, excessive sparking is not good. See

In this vid left condensor (1+4) is bad, right condensor (2+3) is good.

[Greyhound]

Wild guess... Are you running Dyna S electronic ignition??

[exponent]

What kind of meter did you use for testing the wires? Cheap meters are notoriously prone to not having the accuracy or sensitivity to measure small resistances. If it was a cheapo/free Harbor Freight meter, then that is part of your problem.
What exactly was "rebuilt" in the harness? Was the bike running last year after they finished their work?
Why is the fuse missing? Is the fusebox showing any signs of melting around the terminal ends when viewing the back side of the fusebox? They can overheat causing the terminals to become loose and cause problems.

The work order I have says that the main harness was replaced along with the battery, and reg/rec. The bike ran after that. The fuse box looks ok, no damage or corrosion.

[exponent]

Wild guess... Are you running Dyna S electronic ignition??

I don't think so but I'm thinking of getting it just so I don't have to keep messing with these points and condensers.

[Robbo]

Easy test is to swap the two condensers.  If the problem moves from 2/3 to 1/4 you’ve found the problem.


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[RAFster122s]

550s and Dyna S do not work well together because of charging limitations of the bike coupled with the high current draw of the Dyna S. Better to invest in a pair of new coils if needed and install HondaMan's electronic ignition box which uses your stock points as the switching signal. It works very well and improves starting and idling.

Are the middle two plugs dry or wet? They should be wet with fuel if not you are not running on those cylinders...  A clear tube check of float level of each carb is recommended to ensure float levels are properly set and you have fuel reaching the Carb's float bowls.
Are your coils getting battery voltage to them (especially for 2-3)?
Are the plugs firing? Pull the plug and ground it and then attempt to start to see if you are getting a nice blue spark.

[DaveBarbier]

Easy test is to swap the two condensers.  If the problem moves from 2/3 to 1/4 you’ve found the problem.


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