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'76 R75/6: No Spark

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Dan Schroeder
(@dschroeder)
Posts: 9
Active Member
Topic starter
 

I've been working on this bike for a while and it had some minor electrical problems. The motor harness was bad and caused an inconsistent cranking of the starter motor, before this issue the plugs would spark and the inconsistent cranking would prevent the bike from starting. I replaced the motor wiring harness and now the starter cranks as it should, but there is no spark anymore. I checked all the connections on the harness and the coils multiple times. The plugs and cables have been replaced and both coils look alright on the outside and have primary and secondary resistances in the range of where they should be (although I'm not quite sure what it should be exactly). If it helps, I tested to see if the coils were outputting any sort of voltage and the one on the right was while the one on the left wasn't. This has stumped me for a while and I can't think of anything else.

 
Posted : 09/17/2020 09:17
Richard W
(@wobbly)
Posts: 2545
Member
 

These are very simple issues... if you'll think logically and follow an equally logical sequence of testing

• First make sure the ignition switch is supplying full power to Coil #1 on the Green-Blue wire. This is best done with a bulb, and not a meter. 

• Then you can quickly spark the Black "jumper" wire entering Coil #2 (Neg terminal) to some grounding point and see if a brand new plug (laying against the cyl head) will make spark. That will completely test Coil #1 and all associated parts.

• Then move to the Neg terminal of Coil #2 and do the spark test there too. Again with a brand new plug laying against the cyl head. That will completely test Coil #1 AND Coil #2 and all associated parts.

• Then after reconnecting the points lead to the Neg terminal, you can manually operate the points with a screwdriver and see what happens at BOTH plugs. 

That should narrow it down very quickly with a minimum of equipment. 

► In most of these cases, it turns out to be fuel related... which may be why you can't find it in the electrical system. "Bad fuel" will foul spark plugs instantly, and additionally won't burn well enough to crank a bike. The devil is usually in the tiniest details, which don't even make a "blip" on most home mechanic's radar screen. 

Hope this helps.

 

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 09/17/2020 13:44
Dan Schroeder
(@dschroeder)
Posts: 9
Active Member
Topic starter
 

Thank you very much for your response. I've done the tests that you listed. The ignition switch is supplying full power and coil #1 produced a feint spark at the plug when I sparked the jumper wire. However, coil #1 had no spark whatsoever when I did the test. Correct me if I'm wrong, but this means that the coils should be replaced?

Also thanks for the note on fuel. Ill definitely keep that in mind.

 
Posted : 09/18/2020 06:40
Richard W
(@wobbly)
Posts: 2545
Member
 
Posted by: @dschroeder

I've done the tests that you listed. The ignition switch is supplying full power and coil #1 produced a feint spark at the plug when I sparked the jumper wire. However, coil #1 had no spark whatsoever when I did the test. Correct me if I'm wrong, but this means that the coils should be replaced?

► I think you meant Coil #2 on that second entry.

► You are jumping at the bait too fast, my friend. 

• I assume you were testing with brand new plugs ? You didn't say. Because fouled plugs behave the same way.

• No, it merely means something in the #2 "ignition set" needs placing.... either the coil, wire, cap or plug. 4 equally culpable suspects. You can swap those parts 1 at a time with the "good side" equivalents and narrow it down. 

 

The OEM metal housing coils on these bikes are very reliable. About the only way you can kill one is to do ignition testing without a plug laying on the cyl head. There were some fools back in the day that checked carb balance by unplugging one plug cap. That will kill an ignition coil in a hurry. 

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 09/19/2020 19:09
Dan Schroeder
(@dschroeder)
Posts: 9
Active Member
Topic starter
 

@wobbly This certainly helps. Yes I am using new plugs, and you were right about the placing in the coil 2 system. Both can spark now when I ground the system myself. Operating the points doesn't produce anything though. They are recently cleaned and gapped and are receiving electricity. Does this mean its an issue with the wiring to the ground or maybe even the ground itself. Thank you very much for the help so far. I really appreciate it.

 
Posted : 09/20/2020 07:32
Richard W
(@wobbly)
Posts: 2545
Member
 
Posted by: @dschroeder

Both can spark now when I ground the system myself. Operating the points doesn't produce anything though. They are recently cleaned and gapped and are receiving electricity. Does this mean its an issue with the wiring to the ground or maybe even the ground itself. Thank you very much for the help so far. I really appreciate it.

• One more test... I don't trust the points to do their job. They could be incorrectly gapped, still dirty, or other issues. So (ignition ON) I poke a flat screwdriver blade in-between the 2 contacts on the ignition points and wiggle it around. It's quick and easy, and has the best chance of coaxing a spark at the plugs.

If you get a good spark at the plugs, then your points are not gapped correctly, simply not clean, or too old to be useful. Replacement is the simplest move. 

• If that test fails, then (since we know the coils are viable) connect a "test jumper" (wire with alligator clips on each end) between the Neg terminal of Coil #2 and the spring on the points set. If the screwdriver now elicits excitement at the spark plugs, then you have a broken wire between the coil and points, an un-plugged/ disconnected wire between, or some other form of bad connection between.

The only physical connection I know of is at the ignition condenser where the points wire meets the wire coming from Coil #2. Based on the grit (which gets there via water), this union is highly suspect, as is the ignition condenser itself. Reseat (unplug and re-plug) any connector you find there. Apply the screwdriver again.

 

99% of the time it's usually something stupid simple. It takes longer to describe than fix !! I have found where owners have cut wires and twisted the bare ends together. Those type connections are worthless around water. Investigate ANY and ALL repairs covered with electrical tape. Your aim is to return the bike to as close to factory as possible. Because factory condition equates to maximum reliability.

A broken wire inside the stock harness would be the very least likely, that is to say... check the simple stuff first. Learn to read the evidence. Lots of sand inside the cover means lots of water. Lots of water means lots of connector corrosion. (Here remember to include the Points as a "connector".) Owner "repairs" and connector corrosion are where you need to be concentrating. Both are stupid and simple

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 09/20/2020 09:21
Dan Schroeder
(@dschroeder)
Posts: 9
Active Member
Topic starter
 

@wobbly Still no spark either time. I've tested the condenser and its in good shape as is the wire connecting it to the points. They are getting a voltage, but the screwdriver test didn't yield anything. I've since been told it was put away with "a points issue" (that's as specific as I was told). Ill try replacing the points and hopefully that does it. Thanks again

 
Posted : 09/20/2020 12:08
Richard W
(@wobbly)
Posts: 2545
Member
 

Dan -

And what about the "test jumper" to eliminate the possibility of a bad wire ?

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 09/20/2020 13:20
Dan Schroeder
(@dschroeder)
Posts: 9
Active Member
Topic starter
 

@wobbly that yielded nothing as well

 
Posted : 09/21/2020 09:01
Richard W
(@wobbly)
Posts: 2545
Member
 
Posted by: @dschroeder

@wobbly that yielded nothing as well

Ah, so that's what your previous comment meant. I understand now. 

Forgive me, it's been several years since I worked on a points ignition. The wire from Coil #2 does not go all the way to the points, does it? It goes to the ignition condenser or some other connection point near the alternator. (Photos would really help.) Then a long wire on the points goes up through the black rubber tube from the points cavity in the front cover housing to this same "connection point".

Since the jumper did nothing, I agree, the wire from the coil is good. Your issue is 1) in the connection point or connectors adjoined to it, 2) ignition condenser, 3) wire to the actual points, or 4) in the points themselves. 

Hints...

• In the old days, shoddy mechanics hated installing that long points wire up through the black tube. So they would cut that wire on the old and new set of points. Connect the 2 wires together, and hide the new connection up inside the black rubber tube. A shoddy connection may have failed. You'll need to pull the points wire completely out of the black tube and inspect. Do not accept any joints or crimps on this wire. Only the way it left the factory is good enough. 

• If a worker is not careful, it is easy to pinch the 3 yellow alternator wires and/or the points wire between the cover and engine during cover installation. (Don't ask me how I know this.) Getting any of those wires pinched can cut the conductors inside the insulation. Closely inspect for strangely flattened areas on all ignition wires inside the front cover. 

Think Deeply for one moment about how the points work electrically. They are a simple electrical switch.

- One contact (the moving contact) is connected to the points wire and usually the spring. (And nothing else.)

- The opposite contact (the fixed contact) is physically mounted to and thus electrically connected to the aluminum engine block. (And nothing else.)

Put an insulator (paper, plastic, cardboard) between the contact faces and disconnect the points wire at the "connection point". Then verify those facts with an Ohm meter. That test consists of 4 readings. 1) Moving contact connected to points wire, 2) but not the engine block. 3) Fixed contact connected to the engine block, 4) but not the points wire.

See... https://imgur.com/pov6iw9

Some brands of points have a tiny screw at the end of the spring, which attaches the moving contact arm and spring securely to the fixed side of the points set. BUT, there is a stack of important insulators to keep the spring from electrically contacting the fixed portion of the points set. Some intellectual Neanderthals will leave one of these insulators out, or stack them in the incorrect order. Your Ohm reading will tell you this, and disassembly of the stack-up will reveal the reason why it may be happening. 

See... https://imgur.com/mJaLKFl

Like I said... It's very simple and it's right in front of your eyes. 

Hope this helps.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 09/21/2020 10:48
Dan Schroeder
(@dschroeder)
Posts: 9
Active Member
Topic starter
 

The points wire looks a little worn and is pinched in one spot, so that's definitely getting replaced even though it had continuity when tested. However, after the complete removal and reinstallation of the points and condenser I noticed that the points arced (as they would when putting a screwdriver between the arms) when I accidentally touched them with the lead of a multimeter as I was testing to see how insulated the stationary plate was. I gapped them again and the plugs spark now.

I don't know why they didn't arc like this days ago (before I removed them) when I was doing the tests with the screwdriver. My best guess would be that the points wire doesn't always have continuity since its worn and pinched. After replacement it seems like it should work reliably, as there is nothing else that seems to be working out of order.

Thanks again for the help. I appreciate it

 
Posted : 09/21/2020 13:13
Richard W
(@wobbly)
Posts: 2545
Member
 

Good results. Congratulations.

Owning an old Airhead is easy.
Keeping an old Airhead running great is the true test.

 
Posted : 09/21/2020 19:51

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