Evening all.  

please bear with me. 

about at the end of my tether with my project bike.  but it’s fair to say electrics are not my strong point however this RT is getting me down.  Gathering parts I need is going well and had lots of help from people on here, but before I start building it up into a usable bike I want to get it to run.  Getting a spark is proving so difficult for me. Originally there was a weak spark most of the time.  Worth mentioning is that I have the early flywheel with the advance system built in if that’s relevant.

but now I have no spark other than a single spark randomly every now and again and I can’t replicate the circumstances to make it do it to order.  I have read everything I can and tried my best to rectify the issue but am banging my head against my workbench.  

I have replaced points, condenser, coil, plug lead and plug cap and plug.  I have taken the stator plate off and checked for obvious wiring defects.  I don’t know what I am doing with a meter really but have tried to follow instructions I have read on this site and elsewhere.  

I have checked wiring to the coil from the stator.  I have changed items with know working equipment from my RT2 (coil,plug lead cap etc). To no avail. 

could anyone suggest what this random rare spark may be a symptom of? I really am open to anything…. Maybe primary coil/winding?  Is it a rubbish condenser even though it’s new?  I don’t understand it enough really.  Mechanical stuff I can do or learn electrics is sorcery. 

Open to suggestions that I can try.

thank you in advance.   Ian. 

Very frustrating, Ian.

Before anyone asks, points and condenser are new genuine Yamaha, not knock off copies (well, at least that's what I sent to Ian!  ).

Yes. Frustrating. And I did fit the Yamaha parts supplied. Thanks as always Alan.

Spin it with a good drill anticlock of course & make it easy on yourself. Might make it spin easier with the blanked off plug hole open as well. In desperation I've tried the lowest output lighting coil wire fed onto the black at the plug coil but source coil needs isolating or wire unsoldered at condenser. So condenser has points & black heading up the loom. Then with lighting low voltage into black up top it feeds down to the points & condenser. Easy test when ya run out if options but still suspect the source coil when all else fails. Then again lighting coils can fail & cause confusion as ign source earth's Magic into the lighting coil. So on that theory you could earth the source coil direct to the mount post screw. Mine has no lighting coils so just direct earthed to the post. That's mag loom wire straight to the plug coil bypassing the main loom. Just have a way of stopping it if a drama unfolds stuck throttle etc.

I'm not certain how your testing for spark but I'm assuming you are simply using a known good spark plug lying on the cylinder head and connected to the spark plug wire. 

You've done a fair amount of eliminating components by swapping parts. You could eliminate the wiring harness (that could have an intermittent open or short) by doing what RT325 is suggesting near the end of his post.

A single wire ran from the black wire of the magneto harness to the ignition coil is the only wire required to complete the ignition portion of the chassis wiring harness.

The return circuit is via the frame of the motorcycle to the engine cases. So it is important that the ignition coil is properly grounded to the frame and that the frame is grounded to the engine. These grounding connections are typically through mounting hardware and are often corroded and possibly loose which could an intermittent condition.

Thank you both for these suggestions. Really appreciate it.

My wiring harness isn’t the best to be fair and I thought my black wire from the stator harness already went directly to the red wire on my ignition/plug coil. I will have to check. Should I disconnect all other stator harness wires? And just leave the black connected to the coil?

Uncleal also suggested I check if there is a second black wire exiting halfway up from the stator harness and ensure this isn’t connected to anything but I don’t think there is.
Another day at work looms (pardon the pun) then I will get an hour with the bike tonight I hope.

I won’t be starting the bike I just want to get a spark first. And yes I am testing with known plug against cylinder head. I cleaned up the earths on the frame for the coil and my meter tells me that the engine itself is earthed to the frame ok but will also double check again.

All much appreciated. I will update when I can. Any and all ideas welcome. I could well have missed something very obvious but it seems to be pointing at source coil. I really need to get someone who knows how to use a meter to look at that.

Best regards. Ian

"I have no spark other than a single spark randomly every now and again"

Last year Agop had a problem with his AT1-E whereby it would spark once then nothing, kick it over, one spark then nothing.
Manually opening the points I could feel they felt "dampened" and weren't returning to close very quickly so we compared them to the original points which snapped shut.
Swapped the originals back in and all good. 
Turns out the replacements are tight on the pivot meaning they haven't closed before the cam is lifting them again for the next spark, hence why we were only getting the initial spark.
Worth checking them and putting a drop of bearing oil on the pivot.

Don't forget the basics. Clean the point surfaces. Even new points come with a film that can prevent complete contact. A meter should show exactly zero ohms when points are closed every time. If all other things are good, there is a possibility that the source coil insulation is breaking down, causing an intermittant short, but this is fairly rare, and you will not be able to measure it with a meter, since its just a coil of copper wire and the short only appears when the voltage spike happens.

If the black wire from the magneto harness runs directly to the coil connector (which it likely does) then inspect that connection to assure it is tight (the metal female part is actually gripping the bullet) and not lose. If these connections are bent back and forth in an effort to separate them the female part can become deformed and not provide enough grip to create a reliable connection to the bullet. The metal is quite soft and does not have a good memory. I use needle nose pliers and carefully reform the ones I've stretched. The other thing I've found is the contact area of these bullet type connectors are usually oxidized from age and environment. Cleaning (or replacing) them is often required to assure a reliable connection.

One more thing about the black wire, it connects into the main harness to provide a path to ground via the key switch to provide a way to shut the ignition system (spark) OFF. This is why I'm recommending that having only the black wire from the magneto connected directly to the ignition coil. If the bike has a key swich and the harness has not been altered, the black wire, ignition coil input and key switch OFF wire all join together. I don't recall exactly where, I'm guessing at the coil input connection, someone who has an RT1 may be able to confirm this. 

The other wires from the magneto harness are for battery charging and lighting. These are not needed in order to test for spark (and have a running engine for that matter) and by disconnecting them you eliminate the possibility they are contributing to the problem. I can't guess how they could be related to the problem but I do know if they're disconnected it's one less thing to consider as you're troubleshooting. 

I found a schematic that shows the ignition SOURCE coil (in the magneto) is grounded directly at the magneto and is not grounded via either of the other two coils like some other (later?) models.

I've had to replace bullet connectors in order to create a connection that was solid. I've found oxidation between the copper wire and the crimp of these connectors before. So cutting back to clean copper and new connectors were the solution. 
If the black wire connectors are badly oxidized you may want to run a test with the wires stripped and twisted together for testing.

Someone mentioned that Deet on this forum has all the bits to make up these connectors.

Look at the wire from the points to the condensor carefully.  (With a magnifying glass!) Sometimes it doesn't get routed properly and rubs on the points cam just enough to create a pinhole in the insulation.  Fairly high voltage in that wire and the spark pulse can jump to ground if insulation is compromised slightly.

Plug gap set to 0.020 to 0.024 inch?

But mostly I'm thinking you may have consistent spark and not know it!  Try at night or in a darkened garage.  

Back when I was a young teen, I met at a friend's house to go riding in the hills behind his house.  Jeff and his little brother were frantically trying to solve a "intermittent spark" issue after bike wouldn't start.  (We had just been riding the day before with zero issues.). As they kicked it over, I thought I could hear a consistent faint "snap" of a spark, even though the visible blue flash was extremely sporadic.

Jeff's little brother Craig was adamant it was broken when the flash seemed to quit completely.  To settle the argument, I dared Craig to stick his little finger in the plug cap while Jeff gave it a good kick.  It zapped the hell out of him!  LOL

I asked if they were sure it had gas?   Jeff said he had filled it that morning before we went to school so it would be ready to ride after school.  We checked and tank was bone dry.  Turns out his older brother Don skipped school, went riding with his friends, ran completely out of gas, and pushed it home.  Jeff's mom just got home and was kind enough to drive us to the gas station to fill the gas can and we had a nice ride that day.