'77 CB750 point probs

[jamman18]

Long and short of it is I had a bad coil. Got another coil and put it in. Fired up the bike right away and let run for about 5 minutes then shut it down. Watched the points spark as they opened up so all was well!  Went and got my seat to put it on and installed that. Then after another 5 minutes I tried firing it up again and this time it was a no-go!  Now I have no spark at the points, voltage all the way to the connectors for the points harness but no spark or power to the points! I just don't get this! Gotta be something small but not finding it. Any help would be appreciated!

[TOOLS1]

Is your condenser good? The points should not be be sparking. The condenser keeps them from sparking, so they do not burn up. Also when you have your test light on the points it will go out when the points close.
Hope this helps TOOLS

[jamman18]

Yes, some of that does help. What you say about the points not sparking; maybe I should be more exact....When I had it running I had the points cover off and could watch as each point opened up, they create a small "spark" or "zap". This is what other's posts and friends have said what should happen. Here is a good description from one post: "The other side of the coil primaries (blue on one and yellow on the other) go to the points which complete the circuit to ground when the points close. The condensers absorb any extra energy across the points to keep them from arcing.  While the points are closed the coils create a magnetic field in the primary winding. When the points open the magnetic field abruptly collapses inducing a high voltage pulse in the secondary winding which is connected to the spark plug. Then the points close and the process starts over again."  I guess in the long run I am not positive that the condensers are ok.  

Do you have any suggestions on an easy way to test these to see if they ae working properly?

Thanks for the response!

[TOOLS1]

You should see any spark when the points open. The condensers are supposed to absorb the energy so they do not spark and burn the points up.
You can test the condenser by grounding the case to the neg terminal on a battery, and holding the wire on the pos terminal for about 3-5 seconds. Then touch the wire to the condenser case. You should see a spark if the condenser is good.
I once had a bike burning up points. Turned out someone had mounted the condenser to a part that was rubber mounted, and the condenser case was not being grounded.
Good luck
TOOLS

[TOOLS1]

That should read "you should not see any spark"
TOOLS

[jamman]

So how does my not getting a voltage reading past the pin connectors to the points harness figure into this whole thing?

[TOOLS1]

If you are saying that you have disconnected the wires to the points, and are not getting juice through them you might have a break in the wire, a loose connector further back, or a bad fuse. It is just going to take some hunting with a test light and jumper wires.
Good luck
TOOLS

[jamman]

Yes, what I get is 12v when I disconnect on the coil side of the blue/yellow connectors but when I connect them together to go to the points and open the points, then I get no volt reading at the points. I should, shouldn't I? Or would I not if the condensers are bad?  Also, in reference to the fuses, are there any other fuses besides the 3 (1 for the main, 1 for the headlight and 1 for the brake light)?

[TOOLS1]

Now this is getting interesting. If I understand you are getting 12 volts at both sides of the coil. Black and white wire to the coil positive and then getting 12 volts at the coil negative until you connect to the points.
You should be able to hook your test light to a ground then place the prong on the open points and the light go on. When the points close the light should go off, So I am wondering if the points or the wire is grounding out?
Since I understand that you do not have spark through either coil I doubt that the coils are bad, but you can do a continuity check. First disconnect the spark plug wires then connect an ohm meter to the coil wires. You should have continuity.
You also could use an ohm meter to check for the points or wires grounding. Just ground one of the ohm meter leads and place the other on the coil end of the wires. If you have continuity when the points are open they are grounded somewhere.
Again Good luck
TOOLS

[TOOLS1]

I forgot. There are only the 3 fuses. But the first thing I do on any of these bikes is to replace them with Blade style fuses. Its easy. You just cut off the fuse block and wire in 3 of the single blade type fuse holders. Be sure to keep the wires paired correctly though. The main will need a 15 amp and the 2 others will need 7 1/2 amp fuses.
TOOLS

[jamman18]

Well, I checked the condensers and neither one is working so that falls in line with them letting the points burn out in the first place and then still seeing spark at the ponts after replacing them.  Got the new condensers on order. Also, sprayed a little WD40 in both ends of all the pin connectors and now I actually have 12v all the way to the points!  I'll keep you informed after I get the new condensers in.....

[jamman]

Ok, I got the new condensers on the bike today but still no go!  Traced back to find 12v and now I have no power at the points, pinconnectors, coil and have traced back to where the 2 blk/white wires are soldered togehter to supply the 12v to the point and still no power there.  Must be somewhere in the big wiring harness that connects back to the ignition.  My ignition switch, however, went bad and it is bypassed with a toggle switch for all the power. Lights work and starter works.  Tracing the black/white power wire in the harness is going to be hard.  The wiring diagram shows some kind of connector in there but I don't see it at all.

[TOOLS1]

Well Jammin, now your mechanicin
I think you are on the right track now.
TOOLS

[jamman]

I'm glad you have confidence...this is the hardest part as there are a ton of wires that collect behind the headlight....

[jamman18]

I see that on all the diagrams that there should be another pin connector somewhere between where the 2 blk/w wires are fused together that feed the coils and the ignition kill switch.  I just need to know physically where that is so I can check it. Any suggestions?

[jamman18]

Here's a good one for you; tell me if this makes any sense: there are 2 black wires that feed the primary sides of the coils. Just prior to that in line the wires are soldered together to go into 1 wire for the 12v. I plugged in one of the connectors to the coils and checked the other for 12v and got no 12v reading on my meter.This was the same for checking at the solder joint. As I kept the probe on the connector and disconnected the other coil connector I got a 12v reading not only at the connector but also the solder joint. Connected the second one again and lost the 12v reading. What do you make of that?

[TOOLS1]

When you are taking your readings; are the neg side of the coils connected to the points, and are the points open, or closed?
If the points are closed the voltage will be absorbed by the coils.
TOOLS

[jamman18]

Yeahh.....I just figured that out.   The battery was almost drained so i trickle-charged it overnight. When I connected all the wires and opened both points up I got my readings at the points and everywhere else! I wasn't sure until your post if it wasn't maybe the condition of the battery or not.  I haven't, however, had a chance to slap the gas tankk back on and try firing it up. That will be my next thing to do when I get a chance next week.  If it doesn't spark, I'm not sure what to think....got the new coil, points, and condenser, got 12v all the way to the points.....what else could there be?  Can a weak battery have any effect on the ability of the coil to work correctly?  Thanks for the response!
Feel like I m sooo close to figuring this thing out!

[jamman]

Well, I have a 12v reading to both the points, but only when I hold them both open at the same time! I can rotate the crank until one point opens up, take a reading and nothing....open up the other point as well and sure enough, I get a 12v reading!  Same for both points!  So I guess what I want to know is what would be causing this?  It now makes sense as to why I have no spark at the plugs since I have no power at the points when they run normally.  I am the one who put in the new points....is there really a way that I could have installed them wrong to where I would get this situation?

[TOOLS1]

You should have it now. Since both coils, and point sets are supplied from the same power wire; both points have to be open for you to get a reading. As long as one set of points are closed the coil for that set is absorbing the electricity. Are your plug wires, and caps in good shape? I always replace my caps, or boots with NGK parts. A good source is http://www.tasclassicmotorsports.com/ . Also it does take a pretty good charge in the battery to make a good spark. The Honda ignition system is not a very hot firing system. I have heard that iridium spark plugs make a big difference on these bikes, but at $11.00 a piece I have not yet tried them.
TOOLS