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Motorcycle Repair/1978 honda 750K

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QUESTION: This still has points and I am having trouble with the 1-4 set there is a lot of spark coming from them when running.The 2-3 set is running good. It makes you think it would be the condenser but I change it out twice. Also the points them self's and the coil. Nothing changed it. This makes the 1-4 cylinders misfire. Everything else works good.The point gap and timing in good.
  This all started after I had a mechanic remove the engine to replace the head gasket. Any ideas? I have had this bike since 1979 and never had this problem. Thanks

ANSWER: Ed,

In general, arcing points do so because of a weak condenser or dirty contact faces. I recommend that you use OEM Honda parts for the ignition system and not some aftermarket brand.  

Point gap needs to be about .014 to .016" with points just opening at the 1-4 F mark lines. Check voltage readings on each set of points, while the engine is off, then running.

If you have changed the points and condensers more than once and still get arcing despite clean contact faces and the correct point gaps, then you may have a defective or damaged coil. The primary windings should check out about 4.5 ohms. Look also for defective spark plug caps or loose caps on the coil wire ends. Spark plug caps should measure out 5k ohms.

The coils need to be anchored to clean metal on their mounts. Recheck all the ignition settings, good grounds for the points, point plate and engine grounding. Powdercoating/painting of the chassis can sometimes interrupt proper electrical grounds to complete the circuits, so the electricity starts hunting for alternate ground paths. Bad grounds can cause a lot of really weird symptoms.

Bill Silver

---------- FOLLOW-UP ----------

QUESTION: Thanks for the fast feedback. I cleaned the points and reset, which I notice they are honda parts, got my hands on a used coil for the 1-4 side and it did not help. checked all the ground points I could find. All are good to the battery. I have a repair manual with a wiring  diagram.
You mentioned checking the ohms on the coil, from where to where is the best to do this. also is there a way to swap the coils to prove one is bad since the 2-3 side is good?
 Also checked the voltage at the points, OFF about 11 volts RUNNING about 8 volts.
 Thanks

ANSWER: Check the coil primary resistance on the two small wires that feed the coil... Black/white should have B+ voltage and yellow/blue leads go to the points. Disconnect the connectors at the coils and measure out the primary windings there.

Your battery needs to be charged or replaced....  11/8 volts is too low for proper ignition system function. Ensure that your charging system is functioning properly. You should be seeing 12.5+ volts in the system.

You can't easily swap the 1-4 and 2-3 coils due to the lengths of the spark plug wires being different, but you can swap the primary wires from one set to the other and check the spark at the plugs when cranking.

Bill Silver

---------- FOLLOW-UP ----------

QUESTION: Thanks I am finally getting back to you. I had my mechanic check out the coils hoping to see some difference from the 1-4 side to the 2-3, but they both checked out the same. I got my hand on another used 2-3 coil it had the same readings an when installed no change.
 We checked every ground point making sure we had a good contacts, slow charged the battery so now I have good voltage around. Still no improvement on that 1-4 set of points. I,m lot what to o next. Any other thoughts? Thanks

Answer
Do you have full battery voltage on each set of points? If so, really the only thing that makes them arc is a bad condenser or dirty contact faces. Again, make sure you are using OEM Honda parts, not the cheap aftermarket replacements.

Did anything change when you swapped the primary wire connections from 1-4 to 2-3? If the coils are checking out, then the problem is down on the triggering end... points, condenser, wiring connection issues or voltage problems.

Try bypassing the coil wiring harness by connecting some new wires directly down to the points from the coils, just for a test.

Bill Silver

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Bill Silver

Expertise

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.

Experience

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.

Organizations
VJMC (Vintage Japanese Motorcycle Club) of North America

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

Education/Credentials
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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