I need help.  I have exhausted myself chasing a no-spark issue with my 1973 CT3 175.  It ran fine but I decided to do a full restoration on it.  Down to frame and back up.  Engine was rebuilt by a local professional shop. They replaced the points and capacitor and set timing on bench.  I painted the frame and engine myself and reassembled bike.  

Issue is that I now have a very, very weak spark.  So weak you have to be in the dark to see it.  Soft yellow.  I have tried the below to no success.
- sanded bare and ensured ground at frame to engine mounts, at coil bracket to frame mounts, and spark plug to head surface.
- ran jumper ground wire from engine bolt to coil bracket.  
- Coil bench tested good on primary and secondary.  I also replaced it for good measure. Bench tested replacement for good measure.
- Bench tested condenser.  Tested good, but I also replaced it.  Tested replacement as good. 
- Tested stator output.  With coil wire disconnected. I placed lead on engine ground, other lead on coil input from stator and kicked bike over.  Getting 15-17 AC volts on kick.  With coil reconnected I read 10.7 AC volts.
- Tested points with condenser solder circuit in tact.  0.2 ohms with points closed and 2.4 ohms with points open.
- Removed plug cap from coil wire and held bare copper lead 1/4" from engine ground.  Only a very very faint spark in dark. 
- Added starting fluid directly into cylinder and kicked bike, no reaction of any kind from engine. 
- I have tested the bike with all three key positions.  No spark. 

I did have the headlight assembly off of the bike along with the frame wiring harness.  I took many photos before disassembly and feel that everything is back in correct location. However I could have something not plugged in right.  I do not have a wiring diagram with colors for me to check.  

If anyone has any ideas on what I should check next please let me know.  I am at a loss!  And very frustrated.  Lol. 

Thank you 
 

Many stories of aftermarket ignition parts being of very poor quality.

I'm not sure why your shop replaced the points and condenser if it ran fine - presumably they didn't keep the originals?

Anyway, I would fit genuine Yamaha, or Daiichi, points and condenser. Yamaha will be either Hitachi or Mitsubishi parts (can't remember which!) and will have that company's logo stamped on it. Daichi parts will have their logo stamped on them.

I would try and find a genuine Yamaha coil, or maybe an Emgo aftermarket one.

I'm probably out of my depth on some of the electricals, but would note that it is, as standard, a 6v system, so not sure if your higher values are related to your problem.  

if gap around 0.012" and stator output appears to be live, maybe you have grounded the coil during a reassembly.
Is the coil kill switch connection a black w/white wire or solid black?

Pabdt, thank you for the suggestion.  I agree with your line of thought.  I think that I must have something timing the ignition to a ground and acting like a kill switch.  I am not sure how the kill switch circuit works on a CT3 and would to understand it so I can trace/ test the wires to rule that out.  I am not sure what wire is the kill switch wire on this bike?  If you know can you please tell me where to locate it?

My primary coil is currently wired to a factory pig tail as shown below.  I am assuming this is correct.  Would be great for someone on the forum to confirm.  

The wires from the mag are connected as follows.  Again not sure if this is correct. But feel that it is.  
- Black from mag to Black from main harness. (I think this is mag output / coil input wire)
- Light green from mag to Lite green main harness.
- Yellow from mag to Yellow from main harness.
- Green from mag to Green from main harness.
-  Lt Green w red stripe from mag to Lt Green w red stripe from main harness.

Thanks,
Bridger


 

Here are the connections I mentioned above. I am not sure if any of these are kill switch connections?  Appreciate the help with this!

[url= ][img][img]https://i.imgur.com/Va8SA9C.jpg[/img][/img][/url]
[url= ][img][img]https://i.imgur.com/LMbdtv5.jpg[/img][/img][/url]
[url= ][img][img]https://i.imgur.com/YYqzGY4.jpg[/img][/img][/url]

Without reading it all so ignore me if I'm way behind, but go from mag black straight to the coil to see if you get a result. Don't gave anything else into the black if it has a double connector, just straight to the plug coil. Be sure your throttle is free & shutting off. Or have a bit of string on the black to pull & disconnect in the very unlikely event of a stuck throttle. Those carb body's go misshapen after 50 years over tightening & flange ears get pulled which pulls the slide body out if shape & sticks open & if that happens just let the flange nuts go 1/4 turn.
 

That wiring appears to be correct. The *dual wire connector (blk w/white). The routing is like this:

1 wire comes from the KEY SWITCH. When in OFF position, the coil is grounded.
1 wire comes from the stator

You can also tell if its grounded by watching the point gap when you turn it over w/drill counter-clockwise.
If not grounded, the points will be arcing. if grounded, you will see no arc.

I agree w/RT. Sometimes you just got to skip the mess and go straight for the coil. Figure the rest out later.

Pretty sure that there's no kill switch on the CT3.

Just a thought, but while restoring my RT-1B, using the original harness (harness taken off and then back on), a wire in the flasher circuit broke at the steering neck, took me a while to find the bad wire. Harnesses get stiff with age. You might want to check for continuity in the ignition wires.

The old wire harness.. yep,  stiff, brittle, corroded. 

Remanufacturing a harness for my RT1 (70) restoration at tge moment..  gathered all the correct gauge wire, 4mm bullet plugs, 3 ways up front etc , etc.  

I even went as far as creating the old Yamaha clear sleeves that cover the connectors, 1mm walls. Heated crimp over the wire.  Had to look original.. he he. 

RT1B.  Hmm.  Would like one to rebuild.  70-71. Yellow and the red.