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Motorcycle Repair/1976 550f Ignition Coil



i have a crank no spark on my cb 550f,

id thought i check out the coils first because i had tank off.  i checked for continuity on the primary coil and got tone on both sides.  thats the blue wire to the black/white, and the yellow wire, to the black and white.

the manual then says to check secondary for continuity by probing the spark plug wires that lead into both coils.  i got no tone on both sides.  i checked with boots off and probing into wire and with boots on.

in addition, primary coils both had 5.4 ohms resistance, and secondary left had .350 ohms and right side 25.5k ohms.  totally not consistent.

coils are the TEC type made in Japan.  Plug go straight into coils.

ANSWER: Russell, first thought was to have you check the KILL switch and wiring. You should have 12v on the black/white tracer wire from KILL switch to coils. The points are just a switch to turn the coils on and off. If you have power on both sets of points, you should be able to flash across the points with a screwdriver (when they are open) and get spark from one set of coils at a time.

Both coils are identical, electrically, so both should have the same resistance values on primary and secondary windings. Seems like the left coil is shorted out internally.

Bill Silver

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Thanks for the help i figured it out.  The dyna s ignition wasnt getting power from the connector they provided. its a really wired connector.  it self splice into the 12v line into coils.  

i did have a question.  is my tail light suppose to stay on?  1976 550f.  It turn on when i step on brake, and hand brake.  Also works in park.  Just not in the RUN position.

thoughts on that?

ANSWER: Russell, glad to hear that the solution to the ignition issue was fairly simple. Those Scotch-lock connectors can be problematical.

Your tail light, like the headlight is auto-matic ON when you turn the ignition switch to the ON position.
The brake light function is separate from the tail light, so you can't count that portion into the troubleshooting, however if you have a failed ground at the tail light socket or the mounting plate to the fender/chassis, the tail light can act up and do weird things. If it works in PARK position, it "should" work in the ON running position, but take a look at all the ground paths and wiring from the tail light back to the sub-harness connectors on top of the rear fender. for wiring diagrams if you don't have one already. The tail light is also fused separately, I think.

Bill Silver

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Russell back, 1976 honda 550f,  i got bike started and all lights working.

however im getting zero idle...  if i hit the start button and give it some throttle it will stay running.  but as soon as i let off it dies.

where should i start?

Does it run okay with the choke on? They had a fast idle function back then, so if the choke is up about 3/4 on, it should keep running if the idle circuits are all clean.  Once the engine is warmed up, after a couple of minutes, it should run okay... assuming that the engine compression is good, spark timing is correct and carb circuits are all clean and clear. You can get air leaks at the intake manifold rubbers of they are the originals.
If the bike sat unused for more than a few months with old gas in the carbs/fuel tank, then you will have to clean the whole fuel system and check the condition of the gas cap gasket, petcock screen inside the tank, petcock passageways and be sure that the idle jets are all clear. etc.

Even in Hawaii the bikes will need to be choked to get them fired up first thing in the morning and they need warm-up time to keep running once started up.

Bill Silver

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Bill Silver


Need help with vintage Hondas from the 1960s? I am an expert with 250-305cc bikes in particular and most all of the other pre-91 models, in general. I do NOT claim to have a great deal of experience on Gold Wings, Cruisers, ATC/ATVs and dirt bikes.


I have owned/ridden/maintained Honda motorcycles for 35 years. I have written five books on Honda repairs and collecting. I was a service manager for two Honda shops back in the 1980s.

VJMC (Vintage Japanese Motorcycle Club) of North America

VJMC newsletter, as editor for two years and as contributing editor currently.

3 years auto shop in high school, teacher's aide in Automotive Technology in Jr. College, Diesel mechanic course in college, self-taught mechanic and automotive writer.

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