Topic: Ignition point arcing / 2/3 constantly grounded

[Lupo_00]

Hey guys,

73 CB750K Engine
71 CB750K Frame and harness
Pods
4into1 exhaust no mid pipe

I did the 3000mi tuneup (my first time), started the bike, took it for a ride, then started to get some backfiring. Swapped the pilot jets to richen (because I think I’m running lean there), fired it up the next day and it sounded terrible and off timing. Reset the points again, (1/4 gapped at .3mm, 2/3 gapped at .4mm) but here’s where it got weird. The yellow wire is grounding no matter what. I checked all the way up through the harness and it’s not any of that. When there’s a gap at the 2/3 point and the harness is not connected to the coil, I have no continuity no beep (Multimeter lead on engine, and other lead at coil end of the harness). When I hook up the blue and yellow wires to the coils with the 2/3 point open and 1/4 closed, the yellow wire is grounded—and therefore grounded constantly. I start the engine, consistent backfiring, and the 2/3 point is constantly arcing what have I done and what do I do?  Thanks guys.

[Kevin D]

Did you change points and condenser? Put up a photo of the connections. Maybe you got the fiber washers wrong.

[Don R]

 What Kevin said, the points wire needs to be isolated at the screw so the points can make the ground connection.

[Lupo_00]

Photo attached. My only thought is that the point isn’t grounding out when it’s not connected to the coil. It’s when I connect to the coils that it gets constant ground. The condensers are new.

[HondaMan]

Photo attached. My only thought is that the point isn’t grounding out when it’s not connected to the coil. It’s when I connect to the coils that it gets constant ground. The condensers are new.

Lately, "new" condensors does not mean "good" condensors...the only ones I have found that work right lately are the ones from TEC, stamped with their letters. The unstamped ones or the ones with a stylized "D" (for Daiichi) from China are often bad, right out of the package, and/or fail within 1000 miles. Try disconnecting the 'new' condensor to see if that solves the problem...

[johans]

+1   TEC

[Lupo_00]

Photo attached. My only thought is that the point isn’t grounding out when it’s not connected to the coil. It’s when I connect to the coils that it gets constant ground. The condensers are new.

Lately, "new" condensors does not mean "good" condensors...the only ones I have found that work right lately are the ones from TEC, stamped with their letters. The unstamped ones or the ones with a stylized "D" (for Daiichi) from China are often bad, right out of the package, and/or fail within 1000 miles. Try disconnecting the 'new' condensor to see if that solves the problem...

Thanks Hondaman. I tried it out but I’m still grounding out even with the yellow wire disconnected from the point. Yesterday I tested out to the other end of the harness at the coils and it was fine. Somehow it’s grounding out when connected to the coils.

[Deltarider]

I'm afraid I don't understand what you mean. You've been working on the points (and not the harnass) before the problem started, so that's where I would look. Know that grounding of the 2+3 breakerpoint is a known problem. The spade connectors have a crosshead in the vicinity and when not carefully fitted, they are so close that they touch eachother (sometimes intermittently) which leads to grounding.

[Kevin D]

Are you measuring 0 ohms in the photo?

If you set your meter for dc volts you should measure 12v at the yellow wire with it disconnected and the key on and kill switch on.

I'm having my own condenser problems these days.👎
The $10 Daiichi condenser ruined a recent ride. Sparking/sputtering/misfire
The $23 TEK condensers made my CB roar like it is supposed to.

[Lupo_00]

Hey Deltarider, I noticed that with the 2/3 point open, I was still getting continuity between the engine and the the yellow wire at the point. I unplugged the yellow wire by the rear brake switch and I resolved the issue. When the point was open, no continuity between the engine and yellow wire. Closed point had continuity. I plugged back in and unplugged at the coil and it worked properly again. When I plug the blue and yellow into their respective coil leads, I have continuity between the engine and the yellow lead at the point whether the point is open or closed. The 1/4 point works properly—continuity between engine and lead when point is closed, no continuity when point is open.

Hey Kevin D, when I measure for volts with the leads the way they are in the photo, I get about 10 volts.


Am I supposed to have continuity the way the leads are in the photo (one to the engine and one to the yellow wire disconnected from the point)?  That’s what I’m hung up on. Thanks guys!

[Tracksnblades1]

Lupo,

You do realize that the points provide the ground for the respective coils...?
Thus allowing the collapse of the primary winding so the secondary's high voltage spark occurs at the right time.

[Lupo_00]

Lupo,

You do realize that the points provide the ground for the respective coils...?
Thus allowing the collapse of the primary winding so the secondary's high voltage spark occurs at the right time.

Yeah, is it not point open = no ground to coil, point closed = ground to coil?

[Tracksnblades1]

Lupo,

You do realize that the points provide the ground for the respective coils...?
Thus allowing the collapse of the primary winding so the secondary's high voltage spark occurs at the right time.

Yeah, is it not point open = no ground to coil, point closed = ground to coil?

Yes, points open = Secondary's discharge to sparkplugs, and 12vdc through the coils primary and to the points of that coil.

Points closed= completed ignition coil circuit. Primary is charging/charged..

[Tracksnblades1]

I quess why I asked..... how does your point wire (yellow) have 10vdc and shorted to ground at the same time...?

[Lupo_00]

I quess why I asked..... how does your point wire (yellow) have 10vdc and shorted to ground at the same time...?

That's where I am also lost. 

[Tracksnblades1]

Are you blowing fuses...?

[Lupo_00]

Are you blowing fuses...?

Nope, just backfiring consistently...  In my head (and by testing with the meter) it's grounding out somewhere up by the coils.  I'll check again, but the wires weren't bare anywhere, and i saw no contact with the frame.  It's almost as if the ground is passing through the 1/4 coils to the 2/3, but that can't be right. 

[Tracksnblades1]

Lupo,

Kevin D asked if your measuring 0 ohms as pictured with your red lead on the yellow wire and black lead on engine case....?

Were you getting the 10vdc here..? What ohms does your meter read...?

Have you unhooked blue wire from 1/4 closed points....?

1/4 and 2/3 coils share the same 12vdc source wire.

Temporarily disconnect (isolate) coil 2/3 from coil 1/4 where they both plug in to the 12vd switched source wire and see if your problem goes away.....I think your meter is reading from yellow to 2/3 primary to 2/3 1/4 coil 12vdc junction to 1/4 coil primary to blue point wire through 1/4 closed points....

[jgger]

I'm not good at this electric stuff, but love a good puzzle.  On the coils there should be a positive  and negative terminal,  is one of the coils reversed? Or is that even possible?

[Kevin D]

Tracksnblades has it, you should measure 10Ω for two coils from yellow to ground.
Stock coils are 5Ω  each on the low voltage side
Open the 1/4 point, or lift the blue wire, and it should go to infinite Ω.
Do you have Daiichi condensers?
Your points plate says TEK, what are the old condensers?

[Tracksnblades1]

Lupo ,

Kevin’s diagram is indicating this is normal when testing the way you placed your leads with a closed set of points completing the circuit to ground.😃

I would set both points identically at 4mm or .016 and check if your backfiring ceases or increases.

Check your condensers.....

Persistence and bull headed determination usually yields results quicker than wishing and hoping.....

[Bodi]

Looking at your pic it looks OK. Each points connection should have 2 wires, one to the condenser and one to the coil.
If you remove the coil wire from the points (blue or yellow), with key off there should be no connection to ground.
With key and kill switch on, you should see battery voltage at the disconnected coil wires.
Measuring from the points terminal you will see either zero or infinite ohms to ground, depending on whether the points are open (infinite) or closed (zero). You may get some weirdness measuring points open, your meter has to charge the condenser for a second until the reading is accurate. If you see any low resistance with points open the condenser may be bad, try with that disconnected.
Power goes to the coils (through the key and kill switches) and the points ground the coil to complete the circuit. The condenser reduces arcing across the points when they open, points have a short life if the condenser is missing or bad and there's a lot of arcing. With a good condenser you may see very light sparking across the points with engine running in the dark... bright sparks means condenser trouble.
I agree that the measurements you describe make no sense. Unless the points are closed, you should never measure ground on the points to coil wire. Either no connection, or battery voltage if the power is on.

[Tracksnblades1]

Lupo,
As you pictured your ohm meter test, Kevin D has done the Math (heavy lifting) for Faraday’s induction law. If your the book worm type Faraday (law) and Maxwell (formulas) can teach you everything you already tested. As you tested it should show the ohms Kd posted with perfect connections. Maybe a little higher with 40 year old connections. You could isolate each component for a more precise measurement.

[BenelliSEI]

Lupo...... on the point set that is trouble, take the mounting screw that holds the coil and condensers wires on right out. Then inspect the nylon insulator. I recently had one that looked perfect, but was gone on the inside. Replaced it, and all the weird problems disappeared.

[HondaMan]

Lupo...... on the point set that is trouble, take the mounting screw that holds the coil and condensers wires on right out. Then inspect the nylon insulator. I recently had one that looked perfect, but was gone on the inside. Replaced it, and all the weird problems disappeared.

I have also seen the little clip on the points baseplate cut into one of the wires, occasionally touching it (talk about intermittent trouble!) to kill one coil. And, on a 500 I once saw the main harness hanger (those flexible aluminum straps that hold the harness to the frame) cut into a wire, causing a blown fuse once in a while when the turn signals were activated (and the bike hit a bump just right). Intermittent like mad(!).