Author Topic: Another CB550 coil issue  (Read 646 times)

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Offline RevDoc

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Another CB550 coil issue
« on: August 11, 2014, 03:40:26 PM »
Diagnosing issues with the '78 CB550K4 that I'm trying to rehab from being a parts bike at the back of a small repair shop. Both carb and ignition issues due to some hack having been into it. Found this post with another of TT's superb explainations, http://forums.sohc4.net/index.php?topic=5752.0. Having worked for years as an industrial electrician I can appreciate TT's very logical, orderly progession of tests. (TT, I'm sure I speak for many others when I say THANK YOU! for being so gracious in sharing you wealth of knowledge with us.)  Using the list of checks that TT has in the referenced post I found these results:
Stock coils measure~5 ohms: checked ok
Secondaries~15K ohms: had 15.2 & 15.4
Continuity tests:
two primaries: checked ok
Two plug HTs: checked zero
two primaries to HTs: checked ok
OHMS test:
two primaries should have~5ohms+/-1: had 9.2!

This is my first experience with Honda ignition. I don't know if the coils are OEM or something someone just threw on. Markings on the coil bodies look like TEK brand. Left coil has FL703-12V53F Right has FL703-12V53H.

To me it looks like these are toast! If you guys agree, anyone got coils they know would pass testing and how much would they be? Got this bike last Oct. and haven't been able to get more than one hr total riding this summer between the carb hack job and now the ignition.  :'(
Dana

'78 CB550K--Angie
'82 CB750 Custom--Eva



As soon as you straddle a bike expect every other driver on the road to suddenly start competeing for the title "Dumbestsonofa#$%*inallNorthAmerica!!"

Offline TwoTired

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Re: Another CB550 coil issue
« Reply #1 on: August 11, 2014, 05:29:29 PM »
Did you measure secondaries for plug cap the plug cap or from wire conductor to conductor?

Not sure just how a primary can increase resistance, as it is normally a function of the length and size of the wire windings.  If the windings short, the resistance goes down.  If the winding wire breaks, the resistance goes to infinity.

Any physical damage to the coils?

Are you confidant with your meter accuracy and test technique?

Note there is a mistake in the functional test of the FAQ submission.  There needs to be a capacitor(condenser) added in the test to get reliable spark for bench test.  The capacitor aids the coil's stored energy collapse to produce spark.
Lloyd... (SOHC4 #11 Original Mail List)
72 500, 74 550, 75 550K, 75 550F, 76 550F, 77 550F X2, 78 550K, 77 750F X2, 78 750F, 79CX500, 85 700SC, GL1100

Those that learn from history are doomed to repeat it by those that don't learn from history.

Offline RevDoc

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Re: Another CB550 coil issue
« Reply #2 on: August 11, 2014, 08:32:18 PM »
Hi, TT! Sorry, I forgot to include important points. Plug caps were removed for testing the secondary wires. Also, there is a Dyna S system on the bike so, no capacitors. No sign of physical damage to the coil bodies. I haven't had any indication of problems with the meter I used but, will double check with a different meter tomorrow. I agree, the results have me scratching my head too!
Dana

'78 CB550K--Angie
'82 CB750 Custom--Eva



As soon as you straddle a bike expect every other driver on the road to suddenly start competeing for the title "Dumbestsonofa#$%*inallNorthAmerica!!"

Offline RevDoc

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Re: Another CB550 coil issue
« Reply #3 on: August 12, 2014, 09:47:16 AM »
Retested today with my other multimeter. Primaries tested open. Disturbing the wires may have broken one hanging by a thread? If only a couple of strands were left that could account for high resistance...like trying to stuff water flow of a garden hose through a drinking straw!

Have a second set of coils that had the blk/wh wire on one broken off at connection. All tests came in right on the mark. Waiting to get together with a friend who has an electronics repair shop to reattach the lead.

Update: Got the lead resoldered to the coil terminal. Put everything back together and got kickass spark now!
« Last Edit: August 12, 2014, 09:19:39 PM by RevDoc »
Dana

'78 CB550K--Angie
'82 CB750 Custom--Eva



As soon as you straddle a bike expect every other driver on the road to suddenly start competeing for the title "Dumbestsonofa#$%*inallNorthAmerica!!"