Topic: Puzzling no spark question

[arblebang]

Hey guys so I have a 77 CB550 with no spark on 2 and 3. I immediately suspected the coil, so I swapped it out with a couple different used ones, still no spark. I have about 0.2v on the yellow wire going into the 2+3 coil, but just 0.14v on the blue wire going into the 1+4 coil which is sparking well. If you guys could help me diagnose this, it would be most appreciated.

Thanks

[TwoTired]

The points provide a connection to ground (engine case).  When they are closed, no voltage will appear on the blue or yellow wire respectively.
To see a voltage on the blue or yellow wire, the points contacts must be open, the coil provided with 12V on the blk/wht connection, and the interconnect wires must be intact including insulation of those wires.

The power on the blue or yellow wire gets there through the coil from the blk/wht wire connection.  But, it can only be measured when the points are open.

[Rigid]

I'll go out on a limb here and suggest the black wire to 2-3 coil, under the front of the tank, is loose or corroded.

[arblebang]

Many thanks. I think I need to take a crash course on points and condensers. I am off to do some research!

[Rigid]

Missing insulation coating on the inside of the points cover will cause erratic or nonexistant spark also.  The points arc, or are grounded.  I leave the cover off when testing.

[Bodi]

Sorry but I don't know what insulating coating you refer to. I've used original plain metal points covers, aftermarket alloy finned covers, and aftermarket covers with windows - I've never seen any insulation.

For a spark you need very little: a good coil with good cables, +12V at one coil primary wire, and the points connecting the other coil primary wire to ground when closed. You can test the coil without the pints, just have power on one primary wire and touch the other one to a frame bolthead or engine metal . You should get a spark when you lift this wire off the metal. Don't hold the wire conductor as there's a wicked jolt on it when the wire is lifted off.

Lack of spark is usually points related. The post about parts swapping is good; you can go broke swapping out good parts. Find the problem by switching around what you have and testing the individual parts until you find the problem.
I suspect either dirty points or a failed condensor, but a bit of testing will tell. You can test - actually ride for a while - without the condensor(s) but the extreme sparking at the points contacts will destroy them fairly quickly.

[arblebang]

Yeah typically I don't buy anything because I like my projects to progress as cheaply as possible, but I have a huge shed full of old motorcycle parts, with tons of coils lying around. Considering that you'd think I know a thing or two about points, but in fact this is only the 2nd points system I have ever worked on, the first was on my hondamatic and I just swapped out the old points plate because it was completely sized with rust. Anyways last night was fruitful, I did a series of good experiments which led me to believe that the cause of the problem was corrosion on the 2-3 points set. Confirmed, now we have spark albeit weak, so I am off to restore and replace a lot of the crappy wiring from the previous owner: lampwire, speaker wire, solderless connectors, etc.

Many thanks to all

[MoMo]

Sorry but I don't know what insulating coating you refer to. I've used original plain metal points covers, aftermarket alloy finned covers, and aftermarket covers with windows - I've never seen any insulation.

For a spark you need very little: a good coil with good cables, +12V at one coil primary wire, and the points connecting the other coil primary wire to ground when closed. You can test the coil without the pints, just have power on one primary wire and touch the other one to a frame bolthead or engine metal . You should get a spark when you lift this wire off the metal. Don't hold the wire conductor as there's a wicked jolt on it when the wire is lifted off.

Lack of spark is usually points related. The post about parts swapping is good; you can go broke swapping out good parts. Find the problem by switching around what you have and testing the individual parts until you find the problem.
I suspect either dirty points or a failed condensor, but a bit of testing will tell. You can test - actually ride for a while - without the condensor(s) but the extreme sparking at the points contacts will destroy them fairly quickly.

Bodi,  I believe that grey coating on the inside of the points cover is supposed to be insulation.  At least that is the impression I always had...Larry

[bollingball]

photolar why would it need insulation or do you mean from water not elect.? mine has a cork gasket. Don't the screws go through the cover then in the case?

                              Ken

[MoMo]

photolar why would it need insulation or do you mean from water not elect.? mine has a cork gasket. Don't the screws go through the cover then in the case?

                              Ken

Ken,  I think(but I am not positive) that the grey coating smeared inside the cover is an insulating material. If it is, I cannot imagine why it would be needed unless the cover was pushed into the points. The cork gasket is to keep water and dirt out, most of the bikes that come into my shop rarely have that gasket, or if it is there it is so deformed that it doesn't serve its purpose. In the old dirt bike riding days we would goop silicone around any point cover to prevent water from entering-I rarely, if ever, was stranded in the woods...Larry

[Danno]

on cheap or old points the bolt that runs through the points to connect the wire can short out puting an insulator around the bolt before you tighter it down does the trick it can even be a tiny piece of tape you want conduction between the wire and the points not the points and the body of the points which is ground