Topic: K4 - No spark 2-3...sometimes -

[Johnie]

This just happened today.  Took for a ride to heat it up so I could check timing.  Then lost 2-3 and they came in a few times with a burst, then no 2-3 again.  Ended up driving like 5 miles on 1-4 to get home.  Verified no spark in 2-3.  Let motor cool 45 minutes and took off the tank to check connections.  All is well.  Now she fires good again.  I have not had a chance to take it out yet to warm it up and see if it happens again.  I suspect when she gets hot that is when the coils generally fail if I remember right from other posts here.  Am I on the right track guys?  And do you generally replace only the bad coil or do you do both at the same time?  Thanks

[Johnie]

OK, so I checked the connections & took it for a ride.  I could not create the dead 2-3 again.  But it was about 10 degrees cooler than this afternoon.  So am I on the right track...replace that 2-3 coil?

[Rich W]

  Coil going bad ? You running an old ignition ? Is the wiring in your starter switch corroded ?

[OldSchool_IsCool]

I'd suspect many other things before a failed coil.  You mentioned that you checked the wiring.  Could you possibly have had a loose connection that your probing about has maybe temporarily fixed?  I'd double and triple check your ignition wiring.  Clean them up and pack them with dielectric grease.

[Johnie]

 Coil going bad ? You running an old ignition ? Is the wiring in your starter switch corroded ?

Yes, OEM ignition here.  No corrosion anywhere on the bike.  I have not pulled the ignition switch apart yet.  But would that only affect 2-3 cylinders?

[Johnie]

I'd suspect many other things before a failed coil.  You mentioned that you checked the wiring.  Could you possibly have had a loose connection that your probing about has maybe temporarily fixed?  I'd double and triple check your ignition wiring.  Clean them up and pack them with dielectric grease.

Well, 2-3 spark returned once it cooled 45 minutes before I messed with those coil leads.  I will pull all the coil wires apart and put dielectric grease on them.

[myhondas]

Johnie,
I would very much doubt that your coil is bad. Pull plugs and clean, check connection of coil wire at cap(sheet metal screw into the wire) check cap at the spark plug hole for clean. Yellow wire on coil into connector. then check #23 points to make sure that they are clean and gaped properly. then do a timing check.

[Spanner 1]

Could even be the points condenser on 2+3.

[Johnie]

Thanks for the replies.  I have new plugs and new plug caps just installed.  Points were cleaned and gapped last night.  I was just getting the bike warm to check the timing.  I will go over the connections with dielectric and move from there.  Condensor...good point. 

[Johnie]

I thought I heard a bad coil will show itself when the motor is hot.  And once cooled it will work again.  Is this true?

[mystic_1]

Can be true.

Also, check for leaks in your high-tension leads, particularly where they enter the coils.

mystic_1

[Spanner 1]

Very rare, I would think....have seen posts about pick-up coils on CB650's  ( the parts that replace the points ) failing with heat and restoring on cool-down....but not CB750 coils......IMO.

[Johnie]

I will start with new points and condensor.  They were pitted and I cleaned them up the other night.  But the thought went through my head when I saw them, "these should be replaced."  So I will order a set from Z1 today.  That will be a good start.

[phactory]

Johnie,

 I would first install new points and condensers. Also check ALL of the wiring for integrity of the connection and also that there is not corrosion in either end. Also physically remove the coils and look for cracks. When you replaced the spark plug caps did you cut off about a 1/2" and use a fresh part of the spark plug wire?

 Though I would suspect the coil last, it certainly is acting like that is the problem. This is the symptom of a bad coil on many of the BMW's I own.

Good luck, Phil

[HondaMan]

Thanks for the replies.  I have new plugs and new plug caps just installed.  Points were cleaned and gapped last night.  I was just getting the bike warm to check the timing.  I will go over the connections with dielectric and move from there.  Condensor...good point. 

If the points are not in new condition, disturbing the crud with a cleaning can make them intermittent. They must be REAL clean: don't ever use sandpaper or emery paper on them. Use a points file (first choice) or a flat jeweler's file to poish their surfaces, then spray clean with contact cleaner or CRC Brake Cleaner (green lid can), followed by dragging a fresh, white business card through the closed points to wipe the surfaces. They should be smoth and shiny when you're done, or you can have intermittent troubles with the results.