Topic: Coil Resistance Readings

[C317414]

I am troubleshooting an uneven idle issue on my CB550f.  I cleaned and overhauled the carbs, and set the points and timing with a light and dwell meter.  The ignition advance mechanism looks to be in good shape and it is not sticking.  I synchronized the carbs on the bench.  The uneven idle makes it difficult to synchronize them dynamically. 
I want to determine if the ignition components are good prior to looking into other items.  Today, I checked the coils and plug caps with the following results (Readings taken with a Fluke multimeter, with test lead resistance of 0.1 Ω subtracted):


5 Ω NGK plug caps
Resistance ranged from 4.621 Ω to 5.226 Ω, so they are OK (within +/- 10%)

Left Coil (Cyl 2,3)
Primary Winding:  3.9 Ω
Secondary Winding:  14.05 kΩ

Right Coil (Cyl 1,4)
Primary Winding:  4.4 Ω
Secondary Winding:  14.42 kΩ

I understand that coil winding resistance should be 5 Ω primary and 15 Ω secondary.  What are the tolerances for these resistance figures?  Are the above coils OK, or is the left coil suspect?

[scottly]

I wouldn't worry about the coils.

[newday777]

Your coils are fine.
But for the uneven idle, have you put a dial indicator on the
Advancer shaft to check the runout? If someone has tried to turn over the motor using the 23mm nut on the Advancer shaft it's likely the shaft is bent,  and giving you an out of balance points firing.

[bryanj]

550 does not have the shaft like the 750, its a bolt

[Deltarider]

I have used but a 23mm wrench and always did it with the plugs in. Never had a problem. This is just another example of a problem, the CB750 may have had, mistakingly been transported to the CB500/550s. Same for the advancer springs, as far as I'm concerned. Why would you want to cut a coil with an uncertain outcome? If you are annoyed by maybe a somewhat fluttering idle, all it takes is to tweak the coil at the spring's far end a bit (see pic). There's nothing to gain in changing the CB500/550s advance curve, as designed by Honda. The engine is rather tame; four 125cc lawnmower cylinders that happen to share one crankshaft.

[Deltarider]

[...]
I understand that coil winding resistance should be 5 Ω primary and 15 Ω secondary.  What are the tolerances for these resistance figures?  Are the above coils OK, or is the left coil suspect?

Primary: anything between 3 and 5Ω is fine and secundary anything between 13 and 15kΩ.
Realise that the CB500/550s Achilles heel are the sparkplugs and plugcaps. For these models the first check always is: is there a misfire due to a plugcap or HT lead arcing - possibly intermittently - to the head. Back then it was the #1 complaint. Easy to see in the dark or - if your hearing is good - by listening. You could also use a strobe, attach the clamp to the suspect plugwire and point the gun to the floor or wall. I repeat: as far as the CB500/550s it should be the thing to check first. Always.

[C317414]

Primary: anything between 3 and 5Ω is fine and secundary anything between 13 and 15kΩ.
Realise that the CB500/550s Achilles heel are the sparkplugs and plugcaps. For these models the first check always is: is there a misfire due to a plugcap or HT lead arcing - possibly intermittently - to the head. Back then it was the #1 complaint. Easy to see in the dark or - if your hearing is good - by listening. You could also use a strobe, attach the clamp to the suspect plugwire and point the gun to the floor or wall. I repeat: as far as the CB500/550s it should be the thing to check first. Always.

Thanks.  I will check for arcing. 

Where does the coil resistance data come from?  I have searched the internet and have found a few different opinions, but I haven't found any references to manuals from Honda, Nippondenso, etc.

[C317414]

Followup:

I cut a bit from each HT lead and reinstalled the caps.  Then, I ran the engine in a darkened garage and saw no evidence of arcing. 

My gut feel was that the left coil was bad, based on the  3.9 Ω primary winding resistance measurement.  I got a new set of coils, and replaced the left one first.  This solved the issue, the engine runs great and the surge at idle is gone.