Topic: Occasional Loss of Spark Cylinders 1/4

[jd1050]

Hey guys, I have a 1982 Honda Nighthawk CB650SC that I've been slowly bringing back to life over the last couple of years and I'm running into one final issue that I just cannot solve. About once a ride (usually on the freeway but not every time) I will lose spark on cylinders 1 and 4 for about 10-30 secs. I first assumed that the coil was just going bad but I've tested it with a multimeter both cold and hot and it's reading exactly what it should. I've also swapped coils and it didn't move the problem to 2&3 so I'm pretty sure its not the coil. Wires, plugs, boots, and battery are relatively new and in good shape. I then focused my attention on the pulser generator but that also is reading exactly what it should when cold and hot. And from what I've read these rarely go bad. So that leaves the CDI but from my experience these are not the symptoms of a bad CDI as when they go bad they generally just quit working altogether and don't work intermittently as I'm experiencing. Also, an older mechanic once told me that if you compare the resistance values between the two CDI boxes, if they give the same values chances are the CDI is fine. I did check and while I know it isn't conclusive, the values are the same.  Normally in this situation I would just bite the bullet and replace all of the ignition components to avoid the headache but I'm trying to sell the bike and I've already sunk too much money into it. Also, I am 110% sure this is not a fuel/carb issue as every time this has happened I've pulled the plug wires, grounded them with a screwdriver, and observed no spark on 1&4. I am getting extremely frustrated as this is the last thing I need to fix before I sell the bike and I just cannot figure it out! Any insight would be appreciated. Thank you!

[BomberMann650]

If the carburetor float level is too low it will render the engine gutless until the bowl refills to an appropriate level.  This will happen at speed/heavy throttle.  Can you clear tube test the carbs to verify?

[calj737]

Can you explain how you are testing the ignition components when "hot" versus "cold". After idling, after a spirited ride? How long of a ride? Simply being warmed up won't always produce the same results as an intermittent spark loss due to extended riding at a fixed speed.

I doubt its fuel related as this would present itself with more regularity than your intermittent occurrence, and short duration. Possible, but ignition related is my bet.

[Flyin900]

Check the 12V feed to the coil that keeps crapping out to make sure there isn't a pinched/damaged wire in that part of the circuit. In fact run through all the wiring that is part of the CDI, pulsar and 12V coil input sections and make sure all the contacts are clean on the connectors that join each circuit. You should be able to switch the CDI's to do a running check on them as they usually just plug into the main harness and should be switchable? The pulsars really can't be switched unless you have another set to replace these with that are known good.

If your losing that coil entirely then it would seem to be an electrical 12V breakdown and if you already switched coils and it still does it on 1-4 then the wiring or CDI or pulsars would be the likely candidates. So if you switch the CDI's and the same coil quits and all the wiring and connectors are clean and seem good, then pulsars would likely be the last piece of the puzzle.